Programme

The GRAVITY experiment at the Very Large Telescope Interferometer has redefined high-angular-resolution observations of the Galactic Center. Following the precision measurements of the black hole mass and distance, GRAVITY has successfully detected both the gravitational redshift and the Schwarzschild precession in the orbit of stars. Observations of orbital motion and polarized emission from hot gas near the innermost stable circular orbit provide compelling dynamical evidence that the central mass is contained within a few Schwarzschild radii, and that the inner accretion zone is governed by ordered magnetic fields. To date, GRAVITY has tracked the orbits of 18 stars with interferometric precision. A combined analysis of these orbits tightly constrains any extended dark component within the orbit of S2, leaving little room for a significant dark spike near Sagittarius A*. Deep imaging has further revealed ever more stars, some over 100 times fainter than S2 and on shorter and closer orbits. Notably, we report the discovery of a star with an 8.7-year period that approaches the black hole within 140 Schwarzschild radii, offering a new probe for the black hole’s spin. Also the measurement of light deflection - the third of the classical tests of general relativity - is just around the corner. The recent GRAVITY+ upgrade, featuring laser guide stars and enhanced adaptive optics, gives another boost to GRAVITY, setting the stage - alongside with MICADO at the ELT - for the next decade of Galactic Center research.

Using a network of millimeter-wave telescopes around the world, the Event Horizon Telescope (EHT) collaboration has resolved the shadows of both M87* and Sgr A*. I will summarize the progress of the EHT project, including polarized images revealing variability across several years. Across several epochs, and using a variety of distinct image reconstruction algorithms, we consistently recover linearly polarized rings of emission consistent with a Kerr black hole enveloped in dynamic, optically thin plasma. Both linear polarization and multi-wavelength constraints favor accretion flow models with dynamically important magnetic fields. Sgr A* exhibits 24-28% linear polarization on resolved scales, but a significant rotation measure leads to ambiguities in interpreting its EVPA pattern. I will discuss how these ambiguities can be solved in the time domain, as well as the impact of ongoing improvements to the EHT array.

In recent years, the Event Horizon Telescope (EHT) Collaboration has obtained horizon-scale images of SgrA* through millimeter interferometric observations. The Collaboration is now aiming to spatially resolve the time evolution of this radio source by reconstructing a minute-by-minute video of the black hole’s immediate surroundings at horizon scale. This is a particularly challenging task due to the sparsity of the EHT data combined with the rapid variability of SgrA*. The goal of this project is to better understand the black hole accretion dynamics and connect EHT observations with variability detected by other instruments across different wavelengths. This talk will present the VLBI imaging algorithms developed for this purpose, the extensive validation tests carried out to ensure the robustness of the results, and the possible physical interpretation of the reconstructed videos, along with all results published to date.

Sgr A* has long been an object of interest due to its weak accretion and rapid variability. It has been observed for over two decades in various electromagnetic regimes including the radio, sub-millimeter, near-infrared, far-infrared, and X-ray. In this study, we systematically reanalyze all known Chandra X-ray observations of Sgr A* and perform a demographic analysis of the X-ray flare characteristics. We detect ~95 flares ranging from approximately ~10^33 - 10^35 erg/s in the 2–8keV energy band, and find average flare and quiescent rates consistent with existing literature. This study forms the most complete catalogue of Chandra Sgr A* flares to date. As the nearest SMBH, continued analysis of Sgr A* and its variability will help improve our understanding of the fundamental processes driving black hole accretion and outflow.

In the last 50 years, significant progress has been made in understanding how supermassive black holes accrete their gas from megaparsecs to the molecular torus, but the final accretion stages remain unclear. Hiding behind the dust lanes of the Milky Way lies our best chance to study black hole physics, feeding, and feedback, Sagittarius A* (Sgr A*). Here, I present a glimpse of the cool molecular gas surrounding Sgr A* from sub-light-year to parsec scales. I present the first 0.01 pc (0.03 ly) resolution image of the CO(2–1) line, tracing cool (~100 K) molecular gas with sensitivity and resolution improved by two orders of magnitude over previous maps. Comparing with multi-wavelength observations from radio to X-ray wavelengths, this ongoing study reveals a large conical clearing indicative of an outflow and the CO-to-H₂ conversion factor in this environment. This study provides the clearest view yet of how molecular gas feeds Sgr A*.

The time-variable emission from the accretion flow of Sgr A*, the supermassive black hole at the Galactic center, has long been examined in the radio-to-millimeter, near-infrared (NIR), and X-ray regimes of the electromagnetic spectrum. However, until now, sensitivity and angular resolution have been insufficient in the crucial mid-infrared (MIR) regime. The MIRI instrument on JWST has changed that, and we report the first MIR detection of Sgr A*. The detection was during a flare that lasted about 40 minutes, a duration similar to NIR and X-ray flares, and the source's spectral index steepened as the flare ended. The steepening suggests that synchrotron cooling is an important process for Sgr A*'s variability and implies magnetic fields strengths ~ 40–70 G in the emission zone. Observations at 1.3 mm with the Submillimeter Array revealed a counterpart flare lagging the MIR flare by ≈10 minutes. The observations can be self-consistently explained as synchrotron radiation from a single population of gradually cooling high-energy electrons accelerated through magnetic reconnection.

We present results from GRMHD simulations of the accretion flow around Sgr A*, focusing on the formation and dynamics of magnetic flux tubes produced by reconnection near the event horizon. Flux tubes are tracked to measure their orbital motion, velocity, radial position, and trajectories, while intrinsic properties such as size, magnetic field strength, plasma beta, and guide-to-total field ratio are quantified. Multiple simulation runs explore variations in black hole spin and accreting material angular momentum, revealing how these factors influence flux tube formation and dynamics. Our results show that flux tubes can act as coherent, transient structures that may be energized by reconnection along their boundaries and have orbital properties and energetics potentially capable of producing flare-like variability. These findings provide a framework linking flux tube dynamics with observed variability, offering insights into the processes shaping Sgr A*’s high-energy environment.

Faraday rotation is a key systematic uncertainty in interpreting Event Horizon Telescope (EHT) polarimetry of Sgr A*. Unresolved 230 GHz rotation measure (RM) monitoring with ALMA reveals strong intra-hour variability with non-λ² scaling. Nevertheless, the current EHT derotation approach adopts a single median RM assuming the standard λ² scaling, corresponding to a distant (external) screen, although GRMHD simulations predict significant internal Faraday effects. We evaluate the limitations of the current EHT strategy for constraining key polarimetric observables such as the spiral polarization pitch angle, using ray-traced GRMHD simulations initialized from parsec-scale stellar wind models of the Galactic Center. We predict simultaneous multi-frequency RMs at 86, 230, and 345 GHz to guide coordinated RM measurements with future EHT observations of Sgr A*.

The discovery of cold structures around Sgr~A* has challenged our understanding of the gas dynamics and thermodynamic state of the plasma in its vicinity. This works aims to constrain the conditions for the formation of such structures namely the cold disc-like structure and the recently discovered G-1-2-3 complex. We conduct hydrodynamic simulations of the observed Wolf-Rayet stars feeding Sgr A*. Our simulations show that the chemical composition of the plasma is crucial for determining the properties of the medium. We demonstrate that the formation of a cold disc is possible for certain chemical compositions that are consistent with observational constraints. However, it is not possible to reproduce all the properties of the observed disc which might suggest the action of another structure. Additionally, we present our first results on the hydrodynamic modelling of the colliding wind binary IRS 16SW. This is the first step to assess its role on the formation of the G-1-2-3 complex.

Sgr A*'s variable emission has now been detected in the radio, submillimeter, IR, and X-rays. The first detection of a mid-IR flare was made by JWST/MIRI at 5-21 μm in 2024 April. In our initial analysis, we normalized the mid-IR data to remove the unknown interstellar extinction. In this talk, we report a new mid-IR extinction law based on MIRI data in the central 3″×3″ of the Galactic Center. The new extinction law fixes the dereddened mid-IR SED of Sgr A* during the flare. During the flare, the largest 5-21 μm spectral index was α ~ 0.45, and we detected a sudden increase in the spectral index Δα = 0.33, which we propose as a quantitative definition of the flare's start. Extrapolating the corrected mid-IR spectrum to the submm yields a flux consistent with the 220 GHz peak observed by the SMA. These results support a physical connection between the submm and at least a fraction of mid-IR flares, providing a robust framework for interpreting Sgr A*'s time-variable mid-IR emission.

Sgr A* displays intermittent IR and X-ray flaring, possibly due to regions of magnetic reconnection near the event horizon. While this mechanism is favored by both phenomenological modeling and simulations, such methods rely on simplified expressions of the radiating electrons’ energy distribution to model the resulting multiwavelength emission. Rather than this approach, we introduce a new method allowing the electron distribution to vary according to the local plasma conditions. We use a new Bayesian inference framework to directly fit constraints such as Sgr A*’s spectrum, variability, polarization measurements, and Event Horizon Telescope (EHT) images. This fitting produces a data-supported model of the emission from possible magnetic reconnection regions, particularly at EHT-observable millimeter wavelengths. The presence – or absence – of such emission in observations can then provide critical evidence to constrain which mechanisms are responsible for Sgr A*’s variability.

We analyzed 77 epochs of archival Atacama Large Millimeter/submillimeter Array data to investigate flux variability in Sagittarius A*, the supermassive black hole at the Galactic center. Among these, we identified a rare, transient, yet remarkably clear and coherent ∼52-minute sinusoidal modulation at 230 GHz, with a statistical significance exceeding 5σ. Modeling this signal with a Doppler-boosted orbiting hotspot scenario yields an orbital radius of ∼4 Schwarzschild radii and a disk inclination of ∼8° (or 172°), providing the first direct constraint on the geometry of the inner accretion flow at millimeter wavelengths. This nearly face-on inclination is in good agreement with previous constraints from GRAVITY and Event Horizon Telescope observations. These results demonstrate that millimeter-wave periodicity directly probes the geometry of the innermost accretion flow, offering a powerful and independent complement to infrared and X-ray variability studies in the Galactic center.

We present simultaneous JWST, NuSTAR, and VLA observations of Sgr A* on 2024 Apr 05. We report the detection of a strong X-ray flare coincident with a bright IR flare, and a brightening in radio about an hour later. We conclude that the X-ray flare can best be explained by inverse Compton scattering (ICS) of IR flare radiation that is beamed towards the accretion disk. We describe a dynamic scenario analogous to a coronal mass ejection in which a magnetic flux rope is ejected and reconnection produces oppositely directed flows moving upwards towards the rope to produce radio emission and downwards towards the accretion flow to produce X-ray emission due to ICS. IR radiation from the approaching energetic electrons is enhanced by beaming and up-scattered by thermal electrons in the accretion flow to produce the strong X-ray flare. This scenario is consistent with GRMHD simulations in which magnetic flux is sporadically ejected from the inner accretion flow.

The two primary parameters that describe a black hole are mass and spin. The spin value of black holes such as Sgr A* is important for several reasons. For example, the rotational energy of a spinning black hole contributes to the total black hole mass and a spinning black hole leads to asymmetries in the space-time around the hole. New spin values for Sgr A*, and the outflow method used to obtain these values, will be presented and compared with values obtained with other methods, and with values obtained for nearby AGN such as M87*. The implications for the rotational and irreducible mass components of Sgr A* and other implications will be discussed.

The flaring activity of Sgr A*, the supermassive black hole at the center of the Milky Way, provides an opportunity to study the physical processes occurring in the immediate vicinity of an event horizon. Among various interpretations, the hot-spot model - which describes localized, transient regions of enhanced emission orbiting close to the innermost stable circular orbit - has been used to account for observed flare properties, including relativistic modulation of light curves due to Doppler boosting, gravitational lensing, and light travel time effects, as well as variability in polarization signatures. In this talk, I will review the development and astrophysical motivation of the hot-spot model, tracing its evolution from early ray-tracing predictions and phenomenological treatments to more sophisticated simulations. I will show how this model has been used to interpret multi-wavelength flare observations, with an emphasis on the near-infrared and X-ray domains, as well as how it can be applied to interpret recent high-resolution astrometric and polarimetric data from the GRAVITY instrument. Finally, I will briefly discuss alternative dynamical scenarios such as magnetic reconnection or turbulence to account for the observed flaring activity of Sgr A*. The talk will conclude with a short outlook on how upcoming multi-instrument campaigns and next-generation facilities may further test these models and refine our understanding of accretion and emission mechanisms near supermassive black holes.

Multiple phenomena contribute to the observed variability of Sagittarius A*, there's a stochastic red-noise turbulent component and there's a deterministic transient component during high energy flares that seems to be related to a transient orbital motion of hotspots. But what even are these hotspots and why do they appear and disintegrate? We have some theoretical ideas, supported by numerical simulations, that can be tested observationally. There are also spiral pressure waves, predicted by numerical simulations, that may play a big role in the angular momentum transport in advection-dominated accretion flows. We think they could be observed with the high resolution very long baseline interferometry. There is clearly a lot going on around Sagittarius A* and in this talk I will try to systematise what we already know and understand and what we are still hoping to learn with future observations of the Galactic Center.

In this talk, I will discuss research conducted using 'Resolve', a Bayesian interferometric imaging code that can dynamically image the supermassive black hole Sgr A* by combining field theory with observational data from the Event Horizon Telescope (EHT). The 'Resolve' framework lets us exploit temporal and spatial correlations in sparse datasets. A new 'Resolve' extension enables us to separate the dynamic and constant components of the source, paving the way for multi-epoch reconstructions. I will present the first results obtained using this new method, discuss its performance on simulated and EHT data, and explain how it can be used to study time-variable structures in the accretion flow around Sgr A*. More broadly, this approach opens up new possibilities for consistent imaging and variability studies of black hole sources across multiple observing campaigns.

The Galactic Centre (GC) provides the most precise laboratory for testing the spacetime geometry around supermassive black holes. High-precision astrometric and spectroscopic observations of the star S2 have enabled measurements of gravitational redshift and relativistic orbital precession, requiring detailed modelling of all relevant relativistic effects. In this talk, I will show how these observations can be used to constrain the electric charge of Sgr A* within a Kerr–Newman framework. By isolating the charge-dependent contributions to the orbital dynamics, the current S2 data yield an upper limit of $1.26 \times 10^26 C$. This bound lies well below the extremality limit for a $4.3 \times 10^6 M_\odot$ black hole and implies a corresponding constraint on the allowed spin–charge parameter space. I will discuss the robustness of this constraint, its dependence on modelling assumptions, and the prospects for tightening tests of the no-hair theorem with future GRAVITY+ observations.

A large, but not yet observationally confirmed, population of stellar black holes is expected to reside in the S-cluster in the Galactic Centre. One of the possible manifestations of their presence is
gravitational microlensing of the S-stars and transient accretion hot spots around Sgr A*. The typical duration of these events is about 30 minutes. This corresponds to the duration of a multi-wavelength flare of Sgr A* observed in 2019. We argue that this flare, that showed a simultaneous maximum brightening in the individual wavelength bands, can be explained as a microlensing event by a stellar- or intermediate-mass black hole traversing in front of Sgr A*. We also estimate the rate of such events for various parameters of the black hole population.

SgrA* shows flaring events in the near-infrared and X-ray bands several times a day, with multiple flares tracing an orbit around the black hole. We model the relativistic motion of hot spots and provide a direct correlation between the flux eruption events, characteristic of the MAD accretion state, and the observed flaring activity in the Galactic Center (GRAVITY). However, MAD models demonstrate a highly variable accretion flow, in contrast with the low horizon-scale variability of SgrA* (EHT). We investigate accretion disk models with unique magnetic field configurations and implement natural mechanisms for magnetic field dissipation. We generate synthetic observables for direct comparison with the multi-wavelength characteristics of SgrA* and study the observed accretion flow variability. This work imposes constraints on the intrinsic source characteristics and provides a promising framework for understanding the broad spectrum of multi-wavelength observations of SgrA*.

The Nuclear Star Cluster (NSC) of the Milky Way, surrounding the supermassive black hole Sgr A*, provides a unique opportunity to study the formation and evolution of dense stellar systems in the extreme central regions of galaxies. Despite extensive observational and theoretical efforts, key questions remain about its origin, the diversity of stellar populations it hosts, and the apparent absence of a stellar cusp. In this talk, I will present a theoretical and numerical perspective on the formation and dynamical evolution of the Galactic NSC. Using direct N-body simulations, I explore how a combination of dense and massive stellar cluster inspirals and in-situ star formation may have contributed to its assembly. I will discuss various physical processes, including stellar collisions, and how these can influence the NSC's structure and stellar content, potentially contributing to the erosion of a stellar cusp, depending on the black hole's growth and the cluster's dynamical history. I will examine how these models compare with existing observations, and how the combination of improved simulations and data from facilities such as JWST and future instruments like MOONS and the ELTs can help disentangle the formation history of the Galactic NSC—ultimately advancing our understanding of nuclear star clusters and their connection to the formation and evolution of galaxies.

The ability to measure individual stellar motions at the Galactic Center (GC) offers a unique view into the dynamical processes within a galactic nucleus. We present the HST-NSC survey, which leverages 15 years of HST-WFC3IR observations to measure the proper motions of ~200,000 stars within R ~ 7 pc from SgrA*. These measurements achieve a precision as high as 0.03 mas/yr and are tied to the absolute reference frame defined by the Gaia satellite. I discuss initial applications of the HST-NSC survey to explore high-velocity stars that may have been dynamically ejected from the GC. We place the first orbital constraints on the high-velocity stellar maser IRS 9, finding that it was unlikely to have been formed by the tidal disruption of a binary. Alternative mechanisms for IRS 9 include binary supernova disruptions, two-body interactions, and stellar collisions. Identifying additional high-velocity stars near the GC will be essential for understanding these various dynamical processes.

We study the dynamical evolution of stellar binaries orbiting Sgr A*. Through the interplay of von Ziepel-Lidov-Kozai oscillations and tidal friction, these binaries may shrink to near-contact separations. In a novel set of secular-evolution simulations, we find that ~1 in 2 binaries in the central parsec should shrink in this way before their members leave the main sequence. This is a factor ~5 larger than previous estimates, primarily because we consider diffusive stellar tides and gravitational perturbations from passing stars. We discuss how a substantial population of near-contact binaries impacts predictions for X-ray binaries and hypervelocity stars. We then consider the influence of an AGN phase on the dynamics of central-parsec binaries, showing that a massive gas disk induces Hills' mechanism disruptions for some binaries and unexpected shrinking for others. Finally, we discuss the hypervelocity star S5-HVS1 in the context of this work.

The GRAVITY interferometer at ESO’s Very Large Telescope has delivered astrometric measurements of unprecedented precision for the S-stars orbiting Sagittarius A*, enabling direct tests of General Relativity. At the same time, such orbits provide a unique probe of the unseen, extended mass distribution surrounding the central black hole, expected to be composed of a dynamically relaxed stellar cusp and a dark matter spike.

The Nuclear Star Cluster (NSC) at the Milky Way Galactic Center contains a young (4-8 Myr) population with over 100 O, B, and Wolf-Rayet stars. This young nuclear cluster is hypothesized to have formed in-situ, despite strong tidal effects of the supermassive black hole. To date, there is mixed evidence as to whether there is still ongoing star formation in the region. We report on the discovery of a potential young stellar object (YSO) identified by carbon-monoxide emission observed in JWST NIRSPec spectra and corroborated by hydrogen emission from Keck Observatory spectra. The source is significantly reddened compared to the general reddening vector of the region, and has variability in its K' magnitude in the >20 years of Keck observations as well as a velocity dispersion consistent with YSOs in other populations. Orbit analysis places it in good agreement with the young clockwise disk of the NSC. This newly detected source may signify ongoing star formation in the region.

The Galactic center (GC) is home to the largest concentration of exotic X-ray sources in our Galaxy – like LMXBs and CVs – as well as thousands of faint X-ray sources whose nature is unclear. Despite their significance for our understanding of galaxy evolution, binary formation, and other cosmological topics, the classification of most GC X-ray sources has to date remained elusive. We present a comprehensive study of the characteristics and distributions of the various X-ray populations in the GC and the surrounding areas using groundbreaking surveys with the XMM-Newton and Chandra observatories. We find a concentration of hard X-ray sources, consistent with magnetic CVs, in the nuclear stellar disk (NSD). The discovery of MAXI J1744-294, a bright new X-ray transient, provides further evidence for a cusp of black holes in the central pc. Our studies indicate that distinct GC populations are distributed over varying scales, like the central pc, the nuclear star cluster, and the NSD.

I will briefly review the observational evidence of young stars in the central parsec of the Milky Way whose origin is still not fully understood. I will discuss the hypothesis of in-situ star formation in a dense gaseous disc. While being positively accepted in general, the hypothesis has to prove its viability by passing the observational tests. To do so, it is necessary to trace the initial state of the young stellar disc to the evolved one. I will present results of N-body integrations considering evolution of an initially thin and coherent stellar disc due to both internal two-body relaxation and secular evolution as well as the influence of other components of the Galactic center - the old stellar cusp, gas, and putative cluster of compact objects. I will put the model into context of observations of not only the young stars in the Galactic Center, but also other related objects, like the hyper-velocity stars that are being observed far in the Galactic halo.

The Galactic center (GC) of the Milky Way offers a unique laboratory to probe the binary star population in the extreme environment near a supermassive black hole (SMBH). Binary stars offer us insights into the conditions of star formation and they have significant impacts the dynamical evolution of the nuclear star cluster and its interaction with the supermassive black hole. I will discuss work from the UCLA Galactic Center Group leveraging over two decades of adaptive optics imaging and spectroscopy from Keck Observatory to investigate the binary star population within the GC. I will present new measurements of the binary star population, including new binary star candidates, the binary star fraction, and evidence suggesting significant binary interactions. Furthermore, I will explore the implications of these findings for star-SMBH encounters and star formation operating in this extreme environment.

Accessing the true distribution of millisecond pulsars (MSPs) is challenging, especially toward the inner Galaxy. MSPs have long been searched for in the Galactic center (GC), but their radio pulses get dispersed and scattered, making most of them invisible to our shallow surveys. Unveiling a population of MSPs in the Galactic bulge would be a major breakthrough with positive feedback onto many physics questions. One of them is the origin of the mysterious GC excess, either attributed to MSPs or dark matter in the literature. More and more MSPs are now being detected by dedicated, targeted observations toward the GC. PSRs J1740-2805 and J1740-28 are two new MSPs that we recently discovered in deep observations. Interestingly, these two MSPs are just a few arcminutes apart but do not appear to belong to a yet undetected globular cluster. In this talk, I will introduce these two new MSPs and explore what they tell us about the Galactic population of MSPs.

Hypervelocity stars (HVSs) are stars ejected from the Galactic Centre (GC) through tidal interactions with the central supermassive black hole. Combining DESI and Gaia data, we conducted a six-dimensional search for HVSs and identified a compelling candidate, hereafter DESI-312, whose bound trajectory can be unambiguously traced back to the GC. The star resides in the inner halo and exhibits supersolar metallicity, distinct from known populations on radial orbits. Its inferred ejection velocity is consistent with a Hills mechanism ejection, supporting an origin in the innermost regions of the Milky Way. Although an extreme dynamical ejection from a dense cluster cannot be ruled out. Unlike previously identified A- and B-type HVSs, DESI-312 is a 1 M⊙ star on the main sequence or early subgiant branch, thus enabling a detailed chemical analysis of its atmosphere and offering a rare window into the composition of the central regions of the Galaxy, unobscured by dust and crowding

JWST observations of the late-type AGB star IRS 3 (0.2–0.3 pc from Sgr A*) reveal it in its superwind phase, likely approaching the transition to planetary nebula. Spectroscopic analysis detects amorphous silicates consistent with Infrared Space Observatory data. Our enhanced spectral resolution reveals previously unresolved substructure in silicate bending modes, challenging dust formation models. Under the harsh UV radiation of Sgr A*, the dusty envelope of IRS 3 produces refractory material contributing to interstellar building blocks of possible planets. Further, observations of X7 and X8 exhibit complex morphologies suggesting binarity. Finally, MHD FLASH simulations explain observations of the massive Young Stellar Object X3 near the evaporating cluster IRS 13.

The Galactic Center is a unique testbed for understanding star formation and dynamics in the extreme environments surrounding a supermassive black hole. The current orbits of the young stars, which are too young to be dynamically relaxed, provide insight into these processes. With thirty years of high precision astrometric and spectroscopic measurements from W. M. Keck Observatory, we doubled the number of stars with a significant number of accelerations and higher order polynomial terms within the central 0.2 parsecs. We will present the orbital structure of the young stars and new insights into the origin of the S-Star cluster.

Understanding how stars form and evolve in the immediate vicinity of a supermassive black hole remains a fundamental challenge. In this talk, we present new results based on high-resolution NACO/VLT near-infrared imaging with intermediate-band filters, complemented by SINFONI spectroscopy. In the central 0.5 pc, we identify new massive young star candidates and confirm the steep increase of the density of early type stars toward Sgr A* and their top-heavy mass function, which supports an in-situ formation scenario. Extending the analysis beyond the central parsec to previously poorly explored regions at R ~3 pc, we find a predominantly old, metal-rich population (older than 10 Gyr) with additional intermediate-age (2-3 Gyr) and young (∼ 20 Myr ) components, indicating that star formation has also occurred outside the central parsec at more recent times.

We present JWST MIRI-MRS observations sampling of two very different regimes in the central parsec of the Galaxy: 1) a portion of the Circumnuclear Disk (CND), the largest reservoir of matter near the central SMBH and 2) the CND inner cavity, which is exposed to intense radiation from the central cluster of massive stars, but nevertheless shows the presence of both molecular and ionized gas, as well as dust. We present the first spatially resolved mid-IR spectroscopic view of these regions by detecting and mapping over 100 spectral features. These observations provide crucial insights into the physical conditions of the CND, addressing whether current conditions support ongoing star formation. Additionally, analysis of pure rotational H₂ lines in the CND cavity reveals localized molecular gas, challenging current models by confirming H2​ survival in extreme UV fields. More broadly, these results inform models of feedback, and inward transport toward the Galactic center.

For over a decade, astronomers have tracked a population of dusty objects orbiting the Milky Way’s central black hole, revealing complex dynamics and suggesting links to star formation. One model suggests they are stars enshrouded in a gaseous-dusty envelope, which accounts for their infrared excess, emission lines, and stability. Recent observations of D9, a dusty object, revealed that it is a stellar binary. We present numerical simulations of a disk of binary stars in the Galactic Center. The other parameters of the disk closely resemble the observed clockwise disk around Sgr A*. Our simulations show that the binaries in the disk naturally start their infall toward the SMBH and merge due to the KL mechanism. The merging process and merger products may serve as a pathway for the formation of dusty objects like D9. This model compares simulations to the observed population size and orbital distribution, as well as changes in the binary fraction at varying distances from the SMBH.

Since its discovery in 2012, the source G2 has attracted attention as the first tidally interacting, spatially resolved object heading towards Sgr A*. Contrary to predictions, G2 survived the encounter, and more objects with similar properties have been discovered, fueling the debate over whether these are planet-mass gas clouds or dust-enshrouded stars. G2 retains a special interest since it’s the only object observed both pre- and post-periapse. We present new photometric measurements of G2’s dust component, doubling its flux baseline, and discuss the implications on its changing morphology as well as its nature. Additionally, we updated and extended G2’s gas orbital model with new measurements, including the effect of a drag force. With a robust statistical comparison of several models, we confirm that G2’s gas component is interacting with the ambient accretion flow around Sgr A*. These results offer strong observational constraints to the on-going debate of the G-objects’ nature.

We present a computational study of potential tidal effects induced by the supermassive black hole on G objects in the Galactic center. Using well-constrained orbital parameters of the representative G2 source, we model the dynamical evolution of its initially extended envelope in the strong tidal field of Sgr A*. G2’s highly eccentric orbit (e = 0.96) brings it to a periapse distance of 130 au from Sgr A*, subjecting its outer envelope to tidal perturbations and progressive truncation. Our simulations track G2’s radiative properties along one orbit, from apocenter to pericenter, following how tidal truncation and stripping reshape the dusty envelope. To compute the near-IR continuum emission, we employ CLOUDY, a photoionization and radiative transfer code. We place these results in the context of dust-enshrouded sources and merger candidates in the central parsec, where tidal encounters with the black hole shape circumstellar material in the extreme Galactic-center environment.

Within the inner parsec surrounding the SMBH Sgr A*, not only the discovery of surprisingly young cluster of the S-stars was exciting: Several bright L-band emission sources raised questions on their nature. The detection of a prominent Doppler-shifted Brγ line accompanies most of these dust-embedded sources. The interpretation of G2 as a gas cloud moving towards Sgr A* awakened hope to observe accretion processes of a SMBH. Observations of G2 after periapse as well as other G objects challenge the pure gas cloud model and lead to several alternative theories on the nature of these mysterious objects.
In this talk, new observations conducted with various VLT instruments over several decades, and their multi-waveband analysis will be presented. Based on the results, possible interpretations on the nature of the G objects will be discussed. We conclude that a stellar component seems very likely and debate Class I YSO and binary merger models as explanation for the observed properties.

The deficit of cool stars in late stages of evolution in the vicinity of the Galactic centre has long been a known phenomenon. Recently, a novel analytical theory of Zajacek et al. 2020 attributes an important role to the long-term ablation of these stars during their repeated passages through the formerly active galactic jet. We published three-dimensional hydrodynamic models (Kurfuerst et al. 2025) of the ablation of red giants as they pass through a galactic jet with varying density and flow velocity at different distances from the Galactic centre. The study represents the first stage in a project to simulate long-term ablative processes of stars—red giants, asymptotic giant branch stars, and red super-giants—in the vicinity of galactic nuclei. Changes in the structure of red giants can lead to their rejuvenation. We also discuss the influence of this process on the density and morphology of the galactic jet, a process that may explain its observable variability.

In near-Keplerian star clusters, vector resonant relaxation (VRR) reorients orbital planes and can form coherent substructure in angular-momentum space (pairs, clusters, discs). We present a framework for when a massive perturber disrupts this coherence, deriving a criterion from the balance between internal self-torques and the perturber’s differential (tidal) torque, e.g. from an IMBH.

Based on deep Chandra data, we measured the X-ray-derived abundances of Si, S, Ar, Ca, and Fe in Wolf-Rayet (WR) stars from the NSC, Arches and Quintuplet clusters and a field source. Spectral fitting assumes a WR wind composition (H-depleted, C/N-enriched). The Arches and Quintuplet stars show similar Si, S, and Ar abundances but distinct Ca and Fe values, potentially due to dust depletion in Quintuplet. The overall near-solar or subsolar metallicity of the winds suggests internal nucleosynthesis and mixing from parent stars that initially had supersolar metallicity, consistent with the Galactic Centre environment. These results impact our understanding of the region's young clusters and the composition of accretion flow onto Sgr A*.

We revisit the evolutionary status of massive stars at the Galactic Centre (GC) using new stellar tracks (initial masses from 20 to 60 Msun, metallicity Z=0.020) calculated with the Geneva-evolution-code. We adopt updated, lower mass-loss rate recipes for O-type stars and B-supergiants, and higher rates for Red Supergiants. Our models predict that stars lose less mass during earlier phases, leading to less radially homogeneous Wolf-Rayet (WR) stars and the absence of hydrogen-free WN stars. These predictions better match observed WR properties at the GC, especially chemical abundances. We provide updated H, He, and CNO abundances for WR subtypes (Ofpe/WN9, WNL, WN/C, WC) and propose a revised sub-group arrangement for wind-collision modelling. These changes are crucial for accurately modeling the colliding winds from GC massive stars, which directly determines the accretion rate and structure of the gas accreting onto Sgr A*.

Unresolved X-ray emission spreads over the Galactic center region, known as the Galactic center X-ray emission (GCXE), characterized by Fe K$\alpha$ (6.40 keV), He$\alpha$ (6.68 keV), and Ly$\alpha$ (6.97 keV) lines. The Fe K$\alpha$ line originates from cold interstellar matter, while the He$\alpha$ and Ly$\alpha$ lines arise from optically thin plasma with $kT \sim 7$ keV, whose origin has been debated between point sources and diffuse plasma.

According to the No-hair theorem, a black hole is characterized by its mass, angular momentum, and electric charge. The mass of the black hole SgrA* in the Galactic Center has been measured by the GRAVITY instrument at ESO's VLTI to sub-percent precision, leaving the constraint of SgrA*'s spin as a next step.
We present the discovery of a faint star, S301, orbiting SgrA* on a highly eccentric 8.7 y orbit, while approaching it 10 times closer during pericenter passage than the prominent star S2.
This star succumbs strongly to relativistic effects; its predicted maximum in-plane Lense-Thirring precession is comparable to the Schwarzschild precession of S2.
We expect this star to yield a constraint on the spin of SgrA* within the next 10 years, combining GRAVITY's astrometric precision with radial velocity data of the upcoming instrument MICADO at ESO's ELT.
We outline the star's physical properties and discuss a potential migration scenario involving the Hills mechanism.

IRS 13 is a dense cluster near Sgr A* whose stellar content and origin remain uncertain, offering a rare glimpse into the extreme environment of the Galactic centre. The northern sources, IRS 13N, have been proposed as a site of ongoing star formation, with several studies suggesting they are young stellar objects. In this talk, I will present results from combining high-resolution near-infrared photometry with JWST/NIRSpec and MIRI spectroscopy, providing for the first time continuous spectral coverage from approximately 1 to 30 μm. Exploiting JWST’s unprecedented sensitivity and wavelength range, these data show no clear evidence for young stellar objects; instead, IRS 13N appears to consist of a complex mixture of young stars, dust, and gas that are locally heated rather than an active star-forming region.

Finding black holes in the Galactic Center—from the predicted stellar-mass (SBH) cusp to speculative intermediate-mass (IMBH) candidates—requires understanding their environment. We use 3D MHD simulations to investigate these populations across two accretion regimes and predict their observability.

We present the first successful VLTI/MATISSE interferometric observations of the core region of IRS 13, an embedded and evaporating cluster located at 0.13 pc from Sgr A*. Using L- and M-band interferometry, we spatially resolve for the first time the mid-infrared (MIR) environments of the massive central sources IRS 13 E1 and E2, respectively an O5 and a WN8 star. Simple geometric modeling of the interferometric observables reveals compact circumstellar structures with characteristic sizes of a few 100s of au and significant thermal emission. We constrain the relative flux contributions, spatial extents, and temperatures of the emitting components, and investigate possible substructures or stellar companions. Complementary K-band spectroscopy obtained with VLT/ERIS provides additional constraints on the stellar nature of E1 and E2 through BrG and helium line diagnostics. These observations demonstrate the power of MIR interferometry to probe dense and extreme environments in the GC.

Tens of partially resolved radio continuum sources were detected 0.5 pc east of Sgr A*. The sources, clustered in two spatially separated groups, RC1 and RC2, display characteristics of photoevaporative protoplanetary-disk (proplyd) candidates associated with newly formed low-mass stars (Yusef-Zadeh+2015). Their shapes and sizes are consistent with being photoevaporated and photoionized by UV radiation from hot stars in the nuclear cluster, similar to Orion star-forming region. Additionally, IR spectral indices of some sources are consistent with class 0/1 YSOs. Alternatively, they could be bow-shock sources from gaseous clumps interacting with winds from the nuclear cluster or Sgr A* itself. In this talk, I will review multi-wavelength data of the candidates while concentrating on mid-IR spectra from our dedicated JWST program with MIRI MRS to examine the low-mass star formation hypothesis in our GC's inner parsec.

Recent observations obtained by ground-based gamma-ray observatories and neutrino detectors strongly suggested that the Galactic center is likely a prime lab for multi-messenger study. Especially, detection of ultra-high-energy gamma-ray emission from the Galactic center suggests the existence of a hadronic PeVatron located within ~10 pc of Sgr A*. If there is indeed a PeV cosmic ray source and abundant molecular clouds in the surrounding, we expect several different observable effects such as multi-TeV neutrino, gamma-ray photons and electrons. In this presentation, I will discuss our efforts to find traces of the Galactic center hadronic PeVatron using surrounding interstellar medium like molecular clouds and filaments, aiming for a unified picture to explain several high-energy phenomena in the central a few hundred parsecs.

The Galactic Center (GC) is the most extreme environment in our Galaxy, harboring a supermassive black hole, dense stellar populations, and massive molecular clouds. It presents a unique laboratory for studying high-energy processes. Gamma-ray observations from MeV to PeV energies reveal a complex picture of diffuse emission, point sources, and unresolved components. Recent observations of PeVatron signatures probe the limits of particle acceleration in this region. This talk will review the multi-wavelength evidence for cosmic-ray acceleration and propagation in the GC and discuss the implications.

We aim to measure the three-dimensional distribution of cosmic-ray energy density around the Galactic Centre by combining gamma-ray data with a physically motivated 3D gas model of the Central Molecular Zone (CMZ). After separating disk/foreground emission, we identify CMZ clouds as coherent structures in longitude, latitude and velocity space, using H i,
12CO, 13CO and C18O. Cloud seeds are selected around dense cores using pseudo-Voigt peak fitting and a local-height criterion. The clouds are then clustered using agglomerative clustering and inductive clustering methods. The resulting cloud templates are fit to Fermi-LAT data and iteratively merged based on gamma-ray significance, yielding a short list of components detected at > 5σ. Independent distance constraints from CO–OH emission/absorption tomography are incorporated to fit cloud
line-of-sight positions and enable a self-consistent 3D reconstruction of CMZ gas and cosmic-ray energy density.

Very-high-energy gamma-ray emission from the GC is dominated by a bright point-like source compatible with the SMBH, and by diffuse emission from the inner 200 pc produced by accelerated protons propagating through the CMZ. The inferred cosmic-ray density profile suggests steady injection from a source near the GC. We revisit this emission using a spectro-morphological analysis of more than 15 years of H.E.S.S. observations. We investigate the long-term light curve of the central source and study the morphology of the diffuse emission, testing for deviations from a steady-state cosmic-ray density profile. Accounting for large-scale foreground emission, we derive the intrinsic gamma-ray spectrum of the GC diffuse emission and detect significant curvature in the spectrum of the parent cosmic rays pervading the CMZ. We discuss implications for the nature and activity of the central source, cosmic-ray injection and transport in the region, and constraints on the dense gas distribution.

The average H2 ionisation rate in the Central Molecular Zone (CMZ) is several orders of magnitude higher than in the rest of the Galaxy. As photons are rapidly absorbed in this dense region, low-energy cosmic rays (CRs) are the only viable ionising agents. Hence, an enhanced CR density has often been invoked to explain the observed ionisation rates. However, a corresponding excess in gamma rays emitted through interactions of high-energy CRs has not been observed. This discrepancy suggests that any excess CR population must be confined to low energies. To constrain this poorly known low-energy component, we first derive high-energy CR injection spectra using gamma-ray and radio observations, and supplement them with various low-energy components. We then propagate these spectra by numerically solving the CR transport equation using a Crank–Nicolson scheme. By testing multiple CR injection scenarios, we conclude that cosmic rays cannot be the sole ionising agents in the CMZ.

Dark matter (DM) over-densities, or spikes, are expected to form around SMBHs during their growth and may imprint detectable signatures on EMRIs observed by LISA. Sgr A* is therefore a prime laboratory for probing DM. However, most spike models rely on idealised assumptions and neglect key dynamical processes. For the first time, we self-consistently model the evolution of a multi-mass stellar cusp embedded in a DM spike using the 1D Fokker–Planck (FP) equation, finding that mass segregation significantly shortens the DM relaxation time compared to single-mass models. In the innermost region, where the FP breaks down, we show that repeated EMRI mergers eject DM via gravitational slingshot interactions, leading to gradual evaporation of the spike. We find that EMRI-driven heating alone can substantially disrupt, or even erase, DM spikes around IMBHs and SMBHs, in particular Sgr A*, irrespective of previous major mergers. This has important implications for DM detectability with LISA.

Recent X-ray surveys have revealed a new class of sources known as repeating nuclear transients, showing recurrent short-lived activity on timescales from hours to years. A remarkable example, ASASSN-20qc, exhibits quasi-periodic ultra-fast outflows with variable column density every ~8 days during an ongoing tidal disruption event.

The most plausible interpretation involves a compact secondary object, likely an intermediate-mass black hole, closely orbiting a supermassive black hole. As it passes through the accretion flow, it perturbs the gas and produces fast-moving clumps that cause repeated absorption events.

I will present the main properties of such systems and demonstrate how GRMHD simulations can reproduce their observational signatures. I will also discuss how systematic searches for repeating nuclear transients can help identify ongoing extreme or intermediate mass-ratio inspirals and provide targets for future space-based gravitational-wave observatories such as LISA.

The Galactic Centre (GC) is an environment of very energetic phenomena (i.e. the flaring activity of Sgr A*, supernova explosions, emission of stellar origin) that result in the emission of soft (<4 keV) as well as hard X-rays (>4 keV). This environment makes the GC region rich in (apparently) diffuse X-ray emission. In this work, we focus on the 6.4 keV fluorescent line of neutral or weakly ionised iron, a key tracer of X-ray reflection. Using a deep XMM-Newton mosaic covering the GC and inner Galactic disc, together with the stellar mass distribution of our Galaxy, we combine spatial and spectral information to disentangle the reflection signal from other physical X-ray components. We interpret the resulting residual 6.4 keV emission map as the cleanest current estimate of the large-scale reflection signal across the GC. This map provides a valuable framework for future studies, such as low-energy cosmic-ray and polarisation analyses in the Central Molecular Zone.

The Galactic Center remains a puzzling region. In this talk, we consider three observables: (1) the surprisingly high ionization rate in the Central Molecular Zone; (2) the GC gamma-ray emission, including the Fermi Bubbles; and (3) M31 as a Milky Way analogue with diffuse GeV emission extending well beyond a few kpc. Taken together, these datasets reveal a tension between ionization and γ-ray constraints and highlight the possible relevance of non-standard propagation scenarios. We discuss the implications of this combined view and outline future directions.

The H.E.S.S. array of imaging atmospheric telescopes is observing the Galactic Center since more that 20 years. The H.E.S.S. collaboration carried out deep very-high-energy (VHE, E>100 GeV) gamma-ray observations in a 25 degree squared region near the Galactic centre devised to reach the best sensitivity to VHE gamma-ray diffuse emission. We report here on the detection by H.E.S.S. of a VHE emission in the TeV energy regime coincident with the base of the Fermi Bubbles’ emission detected in Fermi-LAT observations. Based on the measured VHE spectrum, possible emissions scenarios are discussed together with multiwavelength and multimessenger signatures.

Magneto-rotational instability is the key mechanism for driving turbulence in accretion disks, which disrupts the axial symmetry of the system and can excite the quasi-normal ringing of black holes (BHs), potentially emitting gravitational waves (GWs). Motivated by this, we investigate stochastic GW signals from turbulent, magnetized disks around BHs. In doing so, we conduct three global GRMHD simulations of (i) standard and normal evolution (SANE), (ii) sub-SANE, and (iii) magnetically arrested disk models. The results from these simulations serve as a source in the Teukolsky equation to calculate the emitted GW energy. We compare the GW signals from these models and identify the aspects of gas physics, including turbulence and magnetic fields, that effectively excite BH quasi-normal modes. We assess whether the stochastic GW generated in each scenario approaches the sensitivity curves of future gravitational wave detectors, offering new insights into multimessenger astrophysics.

The Sgr A* source is surrounded by dense molecular clouds, supernova remnants, and massive stellar clusters with active star formation, all being powerful sources of particle acceleration and non-thermal radiation. The sources emitting Very-high-energy (VHE) gamma rays include a diffuse emission component, also called 'the Ridge', showing a hard power-law spectrum suggesting particle acceleration up to PeV energies.

Efficient cosmic accelerators have been inferred from gamma-ray observations of cosmic ray particles. Supermassive black holes have been considered as potent engines where conditions favorable for efficient acceleration could be maintained. We discuss the acceleration mechanism near a rotating, weakly magnetized and electrically charged black hole. The role of relativistic frame-dragging is prominent within the ergosphere, where it acts on both particles and fields. At the same time, a relatively small but non-zero electric charge is induced on the black hole. By assuming the Kerr metric, we explore the terminal velocity and directionality of various accelerated particles. Notably, in the case of misalignment with respect to the global magnetic field, the interplay of rotation and induced charge increases the terminal velocity of emerging particles. We suggest that this scenario can operate in galactic centers in periods when the black hole transits a magnetic filament.

a system that comes close enough to a galaxies central Massive Black Hole can be disrupted, leading to high energy transients, such as the bright Tidal Disruption Event of a star, gravitational wave emission during the Extreme Mass Ratio Inspiral of a compact object, or a Hyper Velocity Star ejected from a disrupted binary // in this talk i will introduce chaotic 'diving' orbits, where typically distant trajectories can occasionally pass sufficiently close to the MBH to be disrupted - i'll show that these are ubiquitous in evenly modestly axisymmetric potentials (such as our galaxy) at low z-angular momentum - and that divings orbits provide a new and potentially dominant pathway for producing TDEs, EMRIs and HVSs, and a new view of the diversity of orbital dynamics in the center of galaxies, spanning from the sphere of influence out to and beyond the nuclear stellar disc

The Central Molecular Zone (CMZ) of the Milky Way is among the most scrutinized regions of the sky, providing a unique nearby laboratory for understanding the interplay between gas dynamics, star formation, and feedback under extreme conditions. Despite decades of observations, key questions remain about the CMZ’s 3D structure, how gas is converted into stars and planets, and the processes that regulate mass and energy flows. In this talk, I will review our evolving understanding of the CMZ, highlighting new results from recent surveys which offer unprecedented resolution and sensitivity across many orders of magnitude in spatial scales. I will discuss how these programs are reshaping our view of star formation, feedback, and chemical complexity in the CMZ, outline current challenges in interpreting these datasets, and look ahead to how complementary numerical and astrochemical modeling efforts are poised to unlock further insight into our Galactic nucleus.

Isotopic ratios of elements (e.g. D/H, 12C/13C and 14N/15N ratios) measured within interstellar molecular clouds depend on the chemical evolution of the galaxy due to stellar nucleosynthesis and on their physical conditions, and thus they can provide unique constraints to the history of star formation in galaxies. In this talk, I will review the isotopic ratios measured towards the Galactic center, and I will present the most sensitive observations ever obtained of H-, C-, N-, and S-isotopic ratios towards the molecular cloud G.0.693-0.027. The results show 12C/13C of 40 and 14N/15N of 600, two times higher than those expected from the extrapolation of Galactic disk isotopic ratios trend. Astrochemical models have been used to exclude the presence of chemical isotopic fractionation effects because of the high kinetic temperature of the molecular cloud (about 100 K). In addition, the D/H ratio can be used to pinpoint the locations of the future generation of stellar clusters. This method, when applied for the Galactic center molecular clouds, indicates that the degree of deuteration of different molecules, such as N2H+ and HCO+, and their line profiles can be used to reveal the different gas components in the line of sight to the CMZ. Finally, I will also discuss about the nucleosynthesis history and the possible contamination by low-metallicity stars from the Galactic disk through the bars, leading to the measured isotopic ratios in the Galactic center interstellar medium.

We present the ALMA CMZ Exploration Survey (ACES) catalog of compact continuum sources, the most complete catalog of (pre)star-forming sources in the Central Molecular Zone (CMZ) to date. Using an automated dendrogram-based source extraction routine coupled with a by-eye morphological classification procedure, we identify 1735 sources with typical radii of ~0.075 pc that are likely pre/protostellar cores or compact HII regions. We report on the discovery of a previously unidentified population of compact sources that are located at column densities < 10^23 cm^-2, outside of the densest molecular cloud regions. Using metrics from our manual classification, we estimate the aggregate protostellar mass in the CMZ to be ~2.4 x 10^5 Msun, which is ~1.2% of the total dense gas mass in this region. This is nearly ~3.7 times the total star-forming mass estimated from prior catalogs, which implies that the incipient star formation rate (SFR) is potentially higher than previously estimated.

The JACKS (JVLA Ammonia CMZ K-band Survey) provides a wide-area, 1.5″-resolution view of the CMZ, delivering the first core-scale measurements of gas temperature, kinematics, and centimeter continuum across the Galaxy’s central 1.5 degrees. By mapping five NH₃ inversion transitions, RRL, and H₂O/NH₃ masers, JACKS acts as a robust thermometer and unbiased tracer of dense gas motions, enabling accurate core mass estimates and virial analyses complementary to ALMA’s ACES survey. These observations will clarify the CMZ’s multi-temperature gas structure, test if turbulent heating dominates its high temperatures, and distinguish dust, free–free, and synchrotron continuum emission. RRL and maser detections further constrain embedded sources’ evolutionary stages. Together, JACKS and ACES offer a comprehensive view of CMZ star-forming cores. Here we present JACKS’ initial results, including radio continuum and NH3 maps of selected regions, and outline plans to release data to the community.

How gas clouds are transported from the Galactic disk to the central supermassive black hole, SgrA*, remains an important open question. A key step is to understand how gas flows inward from the Central Molecular Zone (CMZ; R~200 pc) to the circum-nuclear disk (CND; R~5 pc). We use hydrodynamical simulations with a zoom-in approach to follow the formation and evolution of the CND self-consistently from the larger-scale flow. We found that: (1) stellar feedback–driven turbulence efficiently drives gas clouds inward, with net inflow rates decreasing from 0.1 to 1e-5 Msun/yr from the CMZ to the CND. (2) The CND forms spontaneously from the large-scale inflow, and perturbations from nearly radial inflow can tilt the CND by ~10-30 degrees relative to the Galactic plane, offering a promising explanation for the observed CND tilt. (3) The CND can obtain mass with inflow rates over 5e-4 Msun/yr in radial inflow events, and reach numbers similar to the observed one (~ 2e4 Msun) within 50 Myr.

Radio surveys of the Galactic Center remain challenging due to limited sensitivity and strong interstellar scattering, making it difficult to detect the pulsars we expect to find there. As a result, the number of pulsars near Sgr A* and their properties are still poorly understood. Recent MeerKAT observations of the Central Molecular Zone have provided an unprecedented view of the Galactic Center and revealed a large population of previously unclassified radio sources at 1.28 GHz. In addition, an ongoing MeerKAT survey at 3.1 GHz, focused on searching for pulsars in and around Sgr A*, will deliver a deep view of this region across the continuum, spectral-line, and time domains. In this talk, I will present current results and ongoing work from these MeerKAT studies.

The Central Molecular Zone (CMZ) of our Galaxy contains a huge reservior of dense molecular gas, yet exhibits distinct star formation characteristics from the solar neighborhood. To explore the origin of the peculiar star formation in the CMZ, we have initiated an observational campaign using facilities such as ALMA, JVLA and JCMT, with the acronym CONCERT. Here we highlight several recent findings (roughly from large to small spatial scales): i) A comprehensive map of dust temperatures and opacity indices in a pc-scale cloud using multi-band ALMA observations; ii) A new class of transient slim filaments of 0.1-pc scales, which may be key to refueling the widespread shock tracers and complex organic molecules in the CMZ. iii) The magnetic field on <0.01 pc scales in several clouds is revealed for the first time and likely regulates gas collapse. iv) With the longest baselines of ALMA, a protocluster is resolved down to 100-AU scales, where protostellar disks and gas streamers are seen.

The Central Molecular Zone (CMZ) is an extreme environment that underproduces stars by an order of magnitude relative to its massive gas reservoir. To investigate this suppressed star formation, we study multiscale density structures of three representative CMZ clouds: cloud e, the 20 km/s cloud, and Sgr C, including cores (0.1 pc), condensations (0.01 pc), and fragments (300 au). We find that these structures are not hierarchical: many cores and most condensations show no evidence of substructure, likely reflecting their pressure-confined and transient nature. While core and condensation separations are broadly consistent with thermal Jeans fragmentation, fragment separations are smaller than the Jeans length, indicating the influence of turbulence or dynamical processes. Compared to Galactic disk clouds, CMZ clouds exhibit a tentative deficit of dense gas on small scales. These findings suggest that extreme physical conditions shape multiscale structures and suppress star formation.

Is the CMZ just a high-density version of the Solar neighbourhood? The peculiar gas dynamics of the inner Galaxy uniquely shaped by the Galactic Bar have a profound impact on ISM properties and star formation. This is quantified through the analysis of high-resolution radiation MHD arepo simulations of a MW galaxy.

Astrochemistry is living a golden age, with more than a quarter of the 340 molecules in the current interstellar census having been detected over the last three years. One of the sources driving this progress is the Galactic Centre G+0.693-0.027 cloud, established as one of the richest molecular reservoirs in the Galaxy. Located in the northern part of the Sgr B2 complex, it hosts unique detections of highly complex organic molecules and key prebiotic species, pushing the actual limits of known interstellar chemical complexity. In this talk, I will present the discovery of a new promising interstellar laboratory, the Galactic Centre G+0.633-0.0604 molecular cloud, which stands as the southern counterpart of G+0.693 within Sgr B2. Sharing similar physical conditions and exhibiting a comparably rich molecular inventory, G+0.633 emerges as an exceptional environment to further explore shock-driven chemistry while probing the astrochemical input for star formation at its earliest stages.

The BISTRO large program at the JCMT mapped the Central Molecular Zone from Sgr C to Sgr B2 in 850um polarized dust emission at a resolution of ~0.5pc. The magnetic field inferred from this polarized dust is highly ordered within the individual molecular clouds. There is an overall trend of magnetic fields on the order of mG in these molecular clouds, which give roughly transcritical mass-to-flux ratios and Alfvenic mach numbers, suggesting magnetic fields may play an important role in providing general support against star-formation. We also find that the magnetic field is strongly preferentially aligned with observationally derived orbital gas flows within the clouds of the CMZ. The observed preferentially aligned magnetic field leads us to hypothesize that in the absence of star formation, the magnetic field in the CMZ is entrained in the orbital gas flows around Sgr A*, while gravitational collapse and feedback in star-forming regions can locally reorder the field.

The origin of the thick gas disk, traced by CO and HI emission in the Galactic Center (GC) region, remains an outstanding problem. Hydrodynamic simulations have successfully reproduced gas accretion and star formation but typically produce very thin gas disks. This discrepancy hampers direct comparison with observations and limits our understanding of the processes shaping large-scale vertical structures. We present results from global magnetohydrodynamic simulations with radiative cooling and heating. These simulations reproduce the observed disk thickness and show that vertical magnetic pressure gradients associated with strong toroidal magnetic fields provide essential large-scale support (Kakiuchi et al. 2024). Further analysis reveals characteristic three-dimensional magnetic field configurations and gas distributions associated with vertical magnetic fields (Kakiuchi et al., in preparation). Such vertical magnetic fields may be relevant to the origin of non-thermal filaments.

The Galactic Center (GC) is known to host a population of metal-rich stars, and there are several measurements of gas-phase metals that hint at, but do not specifically measure, the metallicity of CMZ gas. With JWST, we are now able to map and measure ices across the dark clouds of the Central Molecular Zone (CMZ), which has not previously been possible - prior infrared observatories lacked the resolution and sensitivity. We have measured the column density of CO ice toward several GC molecular clouds, including the Brick, and shown that the CO ice abundance is remarkably, surprisingly high. The CO ice abundance directly implies a higher gas-phase metallicity, since there is more carbon in CO ice than total carbon at Solar metallicity. These measurements also imply that the gas-to-dust ratio is lower in the GC, which changes our estimates of the total mass in clouds. I will put this new measurement in context by highlighting the newly published ACES maps of the CMZ.

Being one of the youngest, densest and most massive clusters in the Galaxy, the Arches cluster provides a unique insight into the lifecycle of massive stars at high metallicity. We will present our team's JWST Cycle 4 observations of the Arches cluster, using NIRSpec's IFU with high resolution gratings (G235H/F180LP and G395H/F290LP). We will showcase the first results of our spectroscopic analysis in the 1.66-5.27 microns range, covering the mass-loss sensitive Brackett, Paschen, and Pfund hydrogen transitions, as well as several temperature and abundance diagnostics. With this, we aim to study the high-mass stellar and cluster physics, the extinction, and the initial mass function (IMF) of the Arches cluster. Our study of the above mentioned sensitive spectral lines, encompassing from the weak to the strong wind regimes, will anchor our understanding of the metallicity dependance of radiation driven winds and stellar mass-loss in the metal rich Universe.

The Galactic Center of the Milky Way is an extreme environment whose activity is sustained by the inflow of material from the larger-scale Galaxy. In roughly half of all spiral galaxies, including our own, this transport is facilitated by a galactic bar, whose dust lane features are thought to channel gas from the Galactic Disk toward the Central Molecular Zone (CMZ). As a result, studying galactic bars is essential for understanding how material is delivered to the Galactic Center, how galaxies evolve, and the initial conditions of the gas before it accretes into the CMZ. I will showcase new ALMA results of the recently discovered Midpoint-GMC, using observations that mirrors ACES. The consistency between the ACES-CMZ and ACES-BAR observations allow us to directly compare clouds in these two regions to better understand the initial conditions of gas before accreting into the center.

Nonthermal radio filaments (NTFs), first discovered at a wavelength of 20 centimeters more than four decades ago, are among the most enigmatic structures at the Galactic Center. They still defy a clear explanation. These striking, thread-like features trace intense magnetic fields and often stand in bold contrast to the Galactic plane. Recent discoveries have revealed surprising connections: some NTFs align well with X-ray threads/features that exhibit Fe He-alpha emission, and others coincide with linear structures observed at millimeter wavelengths. In this talk, I will present results from an ongoing, collaborative, multi-wavelength study aimed at understanding the origins of these filaments. Our findings shed new light on the high-energy processes and magnetic phenomena operating under extreme conditions at the heart of our galaxy.

Galaxy centers are the hubs of activity that drive galaxy evolution. Gas flowing inwards along the bar is deposited in the Central Molecular Zone (CMZ; inner 300 pc of the Milky Way) which then regulates how much of that gas forms stars, is ejected, or flows inward towards the Galactic nucleus. Attempts to uncover the rates of the CMZ energy cycle have been hampered by limited understanding of its 3-D structure. By combining data across the electromagnetic spectrum, we present a comprehensive model for the 3-D structure of the CMZ. We also present a next generation approach that uses machine learning of magneto-hydrodynamic simulations, as well as observational data, to reconstruct the top-down view of our Galaxy’s Center. The 3-D CMZ model can be used to constrain past flaring events from SgrA* and search for gas inflowing towards the nucleus. Finally, we describe how these results affect our understanding of star formation in this extreme region.

Three-quarters of the dense gas in the CMZ is located at positive longitudes and positive radial velocities. Shear should erase the asymmetry in 10 to 50 Myr. Does asymmetry imply a recent injection of gas or an energetic burst of star formation disrupting a sector of the CMZ?
Do the large number of compact 24 um sources at negative longitudes trace a relict population produce by a starburst 5 to 30 Myr ago? I will discuss the "Feedback Ladder" of ever more potent stellar impacts in the context of the CMZ; protostellar outflows, soft and ionizing UV, stellar winds, post-main-sequence mass-loss, supernovae, and accreting but collapsed stellar-remnants such as neutron stars and black holes. Do starbursts fuel and mass-load the Sofue-Handa lobe and the Fermi-LAT bubbles? What is the role of the SMBH and magnetic fields in lofting this material out of the CMZ?

The evolution of galaxies is profoundly influenced by the hot phase of the interstellar medium (ISM), which regulates gas dynamics and drives large-scale outflows. In the Milky Way’s Central Molecular Zone (CMZ), X-ray observations have identified a ubiquitous plasma component at temperatures of ~1keV. However, recent results from eROSITA have challenged the classical paradigm, suggesting that a significant fraction of the soft X-ray diffuse emission—previously attributed to the hot ISM—may instead originate from unresolved low-mass stars. In this talk, I will quantify the contribution of low-mass stars to the ~1 keV emission observed towards the CMZ. By disentangling the stellar component from the truly diffuse hot plasma, I will discuss the revised physical properties of the hot ISM.

The nuclear stellar disc (NSD) is a flattened, dense and rotating stellar structure with total mass of 10^9 Msun that dominates the gravitational field of the Milky Way at Galactocentric radius R<300 pc. Embedded at its centre is the Nuclear Star Cluster (NSC), a spheroidal, moderately flattened and mildly rotating structure with a total mass of 2-3x10^7 Msun and a half-light radius R~5pc. Both the nuclear disc and nuclear cluster are believed to form predominantly from in-situ star formation - the nuclear disc from gas that is transported inward by the Galactic bar that stalls at R~120pc in the ring-like gas accumulation known as the Central Molecular Zone (CMZ), the nuclear cluster from a small fraction of gas that manages to leave the central molecular zone and make its way down to the innermost few parsecs. I will review the structure, dynamics, and evolution of the nuclear disc and cluster, highlighting their connection. I will also discuss the role of the nuclear disc as a tracer of the secular evolution of the Galactic bar. I will end by outlining open questions in the field and future prospects.

Abundance trends as a function of metallicity for different stellar populations in the Galactic Center provide new insights that complement other studies. Since various elements trace distinct nucleosynthetic channels with unique evolutionary timescales, these trends can vary depending on factors such as the star formation rate and gas inflow, thereby revealing differences between stellar populations. I will present a project in which we have succeeded in measuring detailed abundances of nearly two dozen elements for stars in the Galactic Center structures. We find predominantly metal-rich stars, with abundance trends consistent with those of the inner bulge, suggesting similar evolutionary histories. However, we identify a significant and unexplained enhancement in Na abundances. Further studies are required to determine possible evolutionary links to the complex stellar system Liller 1 and metal-rich globular clusters. We find no evidence of typical globular cluster abundance signatures in our Nuclear Stellar Disk stars with sub-solar metallicities.

This study presents a unified high-resolution spectroscopic analysis of stars in the Galactic centre, aiming to characterise the chemical evolution and formation history of this complex environment. By focusing on the nuclear star cluster (NSC), including stars in very close proximity to the supermassive black hole, we explore α-element (e.g., magnesium, silicon, and calcium) abundance trends as key diagnostics for star formation rates and gas-infall history. Our results reveal that the NSC stars exhibit enhanced α-element abundances, particularly in the predominantly metal-rich regime. Notably, the high-resolution observations of stars very near the supermassive black hole show surprising abundance signatures that challenge conventional scenarios of nuclear star formation, suggesting that the stars may have experienced unique enrichment processes that cannot be solely explained by traditional accretion events or capture from dwarf galaxies.

The Milky Way nuclear star cluster (MWNSC) is located together with its surrounding nuclear stellar disc (MWNSD) in the Galactic centre and they dominate the gravitational potential within the inner 300 pc. We reanalyse the low-resolution KMOS spectra obtained by (Feldmeier-Krause et al. 2017,2020) with the aim to improve the stellar parameters (Teff, log g , [M/H]) for the MWNSC. We use an improved line-list, especially dedicated for cool M giants allowing to improve the stellar parameters and to obtain in addition global alpha-elements.
We obtain a high-quality sample of 1494 M giant stars where we see an important contribution of a metal-poor population (~ 20%) centered at [M/H] ~ -0.7 dex while the most dominant part comes from the metal-rich population with [M/H] ~ 0.4 dex. We construct a metallicity map and find a metallicity gradient of ~ -0.1 +/- 0.013 dex/pc favouring the inside-out formation scenario for the MWNSC.

There is no broad consensus on the age and abundance distribution of the nuclear star cluster. I will present new results on the youngest supergiants, which appear to have Solar [alpha/Fe], contradicting earlier work finding elevated [alpha/Fe]. I will also present age/abundance ranges and abundance trends in the NSC that have no counterpart in the Galactic bulge or complex globular clusters. For example, intermedate age stars in the NSC appear to show a 1 dex abundance range. I will present new JWST analysis of the complex globular cluster Ter 5 that may shed some light on what the E-ELT may someday reveal in the NSC. I will also consider how the Galactic bulge population is similar and different from the NSC. The NSC appears to be a unique environment in terms of age distribution and chemical evolution.

We present the measurement of the three-dimensional density profile of the inner r=0.6 pc of the Milky Way’s nuclear star cluster (NSC). This work is the first to use astrometrically measured, projected accelerations of late-type stars to infer their line-of-sight distances. With the astrometric data taken with Keck Observatory over the past 30 years, we are now able to measure accelerations (and higher kinematic orders) for dozens of stars within 0.6pc of the GC. Combining the central r=0.2pc data from Keck and the HST NSC starlist, and using Bayesian statistics, we have investigated what set of density profile parameters best describes the three-dimensional density profile. Our preliminary results show that the value of ɤ~1.75 corresponding to a cusp density profile is less likely, but a “hole” in the profile (negative ɤ values) is also unlikely.

Nuclear star clusters (NSCs) are massive and dense stellar systems found at the centers of galaxies across all morphological types, including the Milky Way. Two main NSC formation scenarios have been proposed: the migration and merger of star clusters such as globular clusters toward the galaxy center, and in-situ star cluster formation from accreted gas. These scenarios predict distinct NSC properties that can be tested observationally.
I will present results from integral-field spectroscopic observations of a diverse sample of galaxies that reveal a clear transition in the dominant NSC formation channel with galaxy mass. While NSCs in dwarf galaxies are primarily formed through the accretion of globular clusters, NSCs in more massive galaxies build a significant fraction of their mass through in-situ star formation. In particular, I will highlight a Milky Way analogue observed with JWST that illustrates the complex interplay of these formation mechanisms within a single system.

The Nuclear Stellar Disk (NSD) is the most prolific star-forming region in the Galaxy when averaged by volume, with an estimated star formation rate of 0.2–0.8 M☉/yr. Recent studies suggest that approximately 10^6 M☉ of stars have formed in the past 〜30,Myr. However, apart from the Nuclear Star Cluster, only two stellar clusters are currently known in the NSD, the Arches and the Quintuplet, which together account for less than 10% of the expected mass of young stars formed during this period. This discrepancy is referred to as the missing cluster problem. The extreme stellar crowding in this region makes it nearly impossible to detect even dense and massive clusters through local overdensity analyses. Nevertheless, they can be identified using proper motions, since members of a cluster/association share similar motions with significantly lower velocity dispersion than the surrounding field population. In this talk, we present a high-angular-resolution, low–proper-motion-uncertainty catalog covering a substantial fraction of the NSD, along with a technique to detect stellar clusters in this extreme environment.

The Galactic centre is the nearest galactic nucleus and the only one where individual stars can be resolved down to milliparsec scales, yet observations remain limited by extinction, crowding, and the small areas covered by existing spectroscopic studies. VVVX-GalCen, an ESO public survey (2026–29), will use the KMOS spectrograph at the VLT (500 h) to characterise ~40,000 stars, providing the first complete, homogeneous spectroscopic data set in the target magnitude range across the central 8,000 pc²—about 20 times larger than any previous survey. Combined with photometric and proper-motion catalogues, it will greatly improve our view of the Galactic centre and deliver strong legacy value. The survey will address key questions, including nuclear stellar disc formation and stellar population, its link to the nuclear star cluster and Galactic bar, and the recent star formation and evolution of young stars. I will present the survey status and preliminary pilot-study results.

We present a dynamical model of the nuclear star cluster described by action-space distribution functions of both the cluster and the surrounding nuclear disc. The model is fitted to a few thousand line-of-sight velocity and proper motion measurements within the central 10 pc, and provides constraints on the mass profile of the cluster and the central black hole, which are compatible with previous studies. A novel aspect of our modelling technique is that it requires only the kinematic information, but not the density profile; despite this, the resulting density is in good agreement with observations.

Nuclear star clusters (NSCs) offer a unique window into the processes driving galactic build-up. They retain imprints of their evolution in their stellar populations and kinematics, the latter reflecting the cumulative effects of mergers, accretion, and internal dynamical evolution. Yet their internal orbital structure remains poorly constrained. I present new results on the dynamics of NSCs in Fornax early-type galaxies using a fully Bayesian line-of-sight velocity distribution recovery code. Its non-parametric framework captures complex kinematic signatures and provides tightly constrained LOSVDs for orbit-based modelling. From VLT/MUSE and SINFONI data, we recover LOSVDs that reveal the multi-component nature of these systems. These results demonstrate the power of Bayesian LOSVD extraction for composite stellar systems and offer the most detailed view to date of NSC internal dynamics, enabling improved orbital decompositions and refinement of SMBH mass measurements.

Nuclear star clusters (NSCs) are building blocks for understanding massive black holes (BHs) and their coevolution with host galaxies. In these systems, dynamical BH interactions drive the formation of hierarchical mergers, distinctive gravitational-wave events and massive BH seeds. However, significant uncertainties remain in the formation of NSCs and their BH populations.
In this talk, I explore how different NSC formation channels shape their BH populations. I model the inward migration of star clusters (SCs) to quantify how hierarchical mergers within the parent cluster affect the BHs delivered to galactic nuclei. I introduce a new population-synthesis framework that self-consistently combines SC dissolution, orbital decay, and BH core dynamics of SCs from detailed cosmological models.
I assess whether this mechanism can seed NSCs with intermediate-mass BHs across a range of host galaxy masses and explore its impact on BH growth and gravitational-wave signals in galactic nuclei.

Nuclear star clusters (NSCs) are the densest stellar systems in the universe, residing at galactic centers and hosting supermassive black holes (SMBHs). We propose a mechanism for SMBH accretion involving the thermally unstable behavior of hot gas produced by colliding stellar winds. While this regime is well-documented in young massive star clusters, where it leads to secondary star formation, it has been less explored in NSCs. These environments differ significantly due to the presence of an SMBH, a massive old stellar population, and a circum-nuclear disk (CND).

Nuclear bars are found in the inner few hundred parsecs of roughly 50% of barred galaxies with Milky Way–like masses. Whether the Galaxy harbors such a feature is uncertain, with severe asymmetric extinction in the Galactic Centre (GC) complicating photometric approaches. We use N-body simulations to identify kinematic diagnostics for detecting a nuclear bar in the Milky Way, accounting for contamination from the main Galactic bar and extinction effects. We identify the vertex deviation of the (v_los, v_ℓ) velocity ellipse as a robust diagnostic for detecting a nuclear bar. Applying this to line-of-sight velocity measurements from KMOS combined with proper motions from VIRAC2, we measure a vertex deviation of l_v = (-63.8 ± 12.5)° for stars within |ℓ| < 0.9° and -0.4° < b < 0.25°. This signal is inconsistent with an axisymmetric nuclear disc and suggests a nuclear bar oriented at α ≈ 60°–75° to the Sun–GC line, providing the first kinematic hints of such a structure in the Milky Way.

The Galactic Center hosts a variety of stellar and gaseous components, including the nuclear stellar disk (NSD), a flat and rotating stellar structure, and the nuclear star cluster (NSC), the densest stellar system in the Galaxy. It also contains prominent gaseous structures such as the circumnuclear disc (CND) and the extended central molecular zone (CMZ). In this talk, I will summarize the key properties of these components, and place the Milky Way’s nucleus in context through comparisons with the centers of other galaxies.

December 9, 2021 marked the launch of IXPE (Imaging X-ray Polarimetry Explorer), the first modern X-ray polarimeter in over 40 years. By adding polarimetry to spectral, imaging, and timing techniques, IXPE opened a new window onto high-energy astrophysics. Among its targets was Sgr A*, the supermassive black hole at the center of the Milky Way, to investigate the origin of X-ray emission from nearby molecular clouds. In this talk, I will show that IXPE detected polarized X-ray emission with a degree of 31 ± 11% and a polarization angle of 48° ± 11°. These measurements are consistent with a reflection scenario, where past flares from Sgr A* illuminated the clouds. The polarization angle points back to Sgr A*, while the high polarization degree suggests that, about 200 years ago, Sgr A* briefly reached a luminosity comparable to that of a Seyfert galaxy.

The center of our Milky Way galaxy hosts a series of energetic outbursts, including the well-known Fermi and eROSITA bubbles, Galactic center chimneys, and the inner 15-pc Sgr A lobes. Are they long-lasting or fast evolving explosive events? What causes these structures? The Fermi and eROSITA bubbles may correspond to typical galactic feedback processes occurring in our own Galaxy in the recent past. Galactic feedback is one central unsolved problem in contemporary astronomy, and the Fermi and eROSITA bubbles are also galactic-scale accelerators of cosmic rays, whose origin remains a century-long mystery. In this talk, I will talk about the possible origins of the eROSITA and Fermi bubbles, focusing on our newly-proposed double-episode jet model. We also use LHAASO, a multi-purpose cosmic ray and gamma-ray detection facility in China, to constrain the Fermi bubble models.

Using multi-line CO observations, we discovered two peculiar cloud complexes (CC1 and 2) located 170–270 pc south of Sgr A*. Their molecular masses of a few 10^4M⊙, comparable to small GMCs, imply that substantial energy is required for them to persist against the strong gravity of the GC. CC1 lies at the bending point of the southern radio bubble revealed by MeerKAT and exhibits a velocity span of ∼90 km/s, unprecedented in the MW. PV diagrams suggest a cylindrical expanding motion with an expansion velocity of ∼30 km/s. Our CO(3–2) data (∼1 pc) resolve CC1 into a network of pc-scale clumps and filaments. The clumps are anti-correlated with substructures in the bubble, and their velocity widths increase toward the bending point (Enokiya+, in prep.). We propose that a past nuclear jet interacted with these cloud complexes, colliding with and disrupting CC1, producing split jet streams around the clumps and driving the observed expansion, as seen in jet–ISM interaction simulations.

X-ray observations of the GC diffuse emission have been performed for more than thirty years, revealing an intense and highly-variable non-thermal component spatially correlated with the main molecular complexes. This reflection signal has been identified as echoes created by the past activity of Sgr A*. Time behaviors and spectra across the whole CMZ, along with recent polarization data, are successfully explained by several short outbursts during which Sgr A* was at least a million times brighter than today. While propagating away from Sgr A*, these events provide a tomography of the CMZ. However, we currently do not have enough information on the past light curve of Sgr A* nor on the 3D distribution of the molecular clouds at the GC to fully interpret it. In recent years, we have connected efforts made on both aspects to understand how X-ray echoes can inform 3D modelling of the CMZ and how recent 3D models of the CMZ constrain Sgr A*’s past activity. I will present our results.

We present the results of a new deep survey of neutral hydrogen above and below the Galactic Center with the Green Bank Telescope. Previous observations reveal the existence of a population of anomalous high-velocity clouds extending up to heights of about 1.5 kpc from the Galactic plane and showing no signature of Galactic rotation. By modeling the cloud kinematics, the clouds are consistent with an outflow expanding from the Galactic Center. However, a number of HI clouds at lower velocities predicted by the model were missed in previous observations. In this talk, I will present our recent progress with new deep observations. We decompose and identify a large number of hidden HI clouds at lower velocities. These low-velocity clouds have lower column density, smaller sizes, and are less massive compared to high-velocity clouds. Including the low-velocity gas, the outflow rate and wind kinetic power will be a factor of 2 larger than previous results.

The X-Ray Imaging and Spectroscopy Mission (XRISM) realizes the first-ever non-dispersive high-resolution X-ray spectroscopy, which enables us to precisely determine the ion temperatures, ionization states, and velocity structures of diffuse sources typified by supernova remnants. XRISM observed the supernova remnant Sgr A East in February 2024. The Fe-K spectrum of Sgr A East showed narrow (~109 eV in 1 sigma) He-like lines as well as low-ionized (Be-like, Li-like, etc.) lines and enhanced forbidden-to-resonance ratio (~1.4). Our findings suggest that the plasma is in a highly "over-ionized" state, indicating that the remnant experienced a rapid ionization or thermalization, neither of which is expected in the standard evolution. We conclude that one of the possible origins of this over-ionization is a bursting activity of Sgr A* a few thousand years ago (XRISM Collaboration, 2024, PASJ, 74, 1). I will review what we have learnt with XRISM about Sgr A East and the surrounding environment.

For decades, chemical studies in external galaxies have been limited by sensitivity, resolution, bandwidth or a combination of them. A decade of ALMA operations, made the detailed study of the molecular abundances in nearby galaxies a routine job. We can finally bridge the ISM chemistry from Galactic to extragalactic environments, through one to one comparison, albeit probing significantly different scales. The ALMA large program ALCHEMI imaged the chemistry of the starburst galaxy NGC 253 at an unprecedented combination of sensitivity and resolution, achieving a detailed spatially resolved chemical inventory. We probed molecular differences among regions within its CMZ, and to compare with Galactic environments ranging from hot cores, quiescent molecular clouds and comets. This comparison can be put in the context of available data towards other extragalactic environments. The wideband sensitivity upgrade of ALMA will expand similar comparisons towards a wider range of Galactic and extragalactic objects.

NGC 253, the nearest nuclear starburst, is an ideal analog for observing the secular evolution of a Milky-Way like nucleus during a high-activity phase. Its proximity allows for parsec-scale observations of the intense star formation in its nucleus which hosts ~14 young, massive embedded super star clusters (SSCs) and has launched a multiphase superwind with a total mass comparable to the molecular gas mass of the entire Milky Way nucleus. We present new JWST observations of an expanding shell around one of the most evolved of the SSCs, measuring its properties to probe how this early-stage feedback relates to the superwind. Our results highlight the limitations of using the present-day GC to infer conditions at higher-activity times and provide direct evidence that even in the strongly-sheared environment of a barred nuclear potential, individual SSCs can carve out coherent structures on tens of parsec scales and inject significant energy and momentum into the surrounding ISM.

Despite decade-long efforts, the way supermassive black holes (SMBHs) in Galactic Centres accumulate their mass is still not determined. One possible contribution is supernova-driven expanding shells, which may deliver swept-up interstellar matter to the close vicinity of the SMBH. This process is presumably the most effective in the circumnuclear disk (CND), where the supernovae explode in a dense environment at a few parsec distances from the Sgr A*.
We follow the impact of stellar explosions nestled in or near the CND with 3D magneto-hydrodynamic simulations. We detect a temporary increase in the accretion rate of the disk, transferring an additional 2-60 M⊙ of gas to the immediate vicinity of the SMBH, depending on the explosion site. At the same time, the kinetic energy of the SN blows away even mass from the CND; the additional gas leaving the disk within ~100000 years after the explosion is in the order of ∼ 100 M⊙.

We investigate the 7′ radio halo surrounding the Sgr A complex toward the Galactic center (GC) using HI 21 cm absorption measurements to constrain its distance and physical association. Strong HI absorption detected near −53 km s⁻¹ toward all halo regions is attributed to the 3 kpc arm, placing the halo at a minimum distance of ≳5 kpc. We further examine HI absorption toward five distinct halo parts. Absorption associated with the +50 km s⁻¹ GC cloud is observed toward only three regions. However, strong CO and CS emission from the same cloud is detected toward all five parts. This combination implies the halo is situated partly behind and partly in front of the +50 km s⁻¹ cloud. These results provide the first clear evidence locating the 7′ halo at the same distance as the +50 km s⁻¹ cloud, firmly within the GC region, likely created by energetic activity approximately 10^5 years ago.

The Nuclear Star Cluster is the richest cluster in terms of massive stars across the whole Galaxy. However, it is unclear how unique it is with respect to others. In this work, we assess this question through calculating mock spectra of within the central five parsecs integrated Nuclear Star Cluster using the stellar population synthesis models of HR-pyPopStar for single stars and BPASS for binary stars based on the most accurate observational data. We first check the spectra by testing against NIR broadband integrated observations of the Galaxy center. Then, we present our first results, compared the resultant spectra with available data of nuclear star clusters of other nearby galaxies to compare the Star Formation Histories and variations possible variations on the Initial Mass Function.

While Sgr A* supermassive black hole is currently underluminous, it is known to exhibit transient flares, presumably caused by episodes of material inflow that gives rise to spots or self-crossing shocks, possibly originating from a tidal disruption event. These features have been detected in different spectral bands, and they presumably arise in the relativistic region. It has been suggested that the light curves are intrinsically of stochastic nature, further modulated by the debris motion. We discuss the temporal asymmetry in the mock lightcurve fragments as a signature of relativistic effects present in the signal. The defining parameters are those of the intrinsic light curve generated from a distribution of spots or shocks in the accretion plane, the black hole spin, and the view angle of the observer.

The Galactic Center X-ray Emission (GCXE) remains largely unresolved and exhibits prominent Fe Kα (6.4 keV), Fe Heα (6.7 keV), and Fe Lyα (6.97 keV) emission lines. Part of the GCXE is attributed to the superposition of X-ray active stars (XASs), including magnetic and non-magnetic cataclysmic variables (mCV, non-mCV) and active binaries (AB), of which only ~10–40% has been resolved, leaving the origin of the remaining component unclear.
XRISM observed a region 9′ west of Sgr A* in 2024. Using the high-resolution X-ray spectrometer Resolve, we applied an XAS model consisting of mCV, non-mCV, and AB, incorporating motion velocities, to fit the GCXE spectrum. The XAS model failed to reproduce the fine structure of the Fe lines. The residuals can be partially accounted for by an additional plasma component, especially a recombining plasma with electron temperature ~1 keV, which may be a truly diffuse plasma influenced by past activity of Sgr A*.