Feeding and Feedback in the Nucleus of our Galaxy

• Applicant: Professor Dr. Andreas Burkert
• Subject Area: Astrophysics and Astronomy
• Term: from 2017 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 328058720

• Final Report Year: 2020

Final Report Abstract

The most up-to-date telescopes and instruments have offered an unprecedented opportunity to study the extreme environment surrounding supermassive black holes (SMBHs) in nearby galactic nuclei. Understanding the physics of these exotic objects, living in the center of most galaxies, is crucial to test General Relativity and to shed light on their impact on galaxy formation and evolution. A particularly good laboratory is our own Galactic Center, where continuous monitoring of the orbits of the young star (S-star) cluster in the inner few light months from the SMBH has allowed a precise derivation of its mass. Still, many uncertainties exist concerning the gas distribution at those distances and its accretion from the Bondi radius up to the black hole event horizon. In a first project, we tested whether the winds of the S-stars can be used as diagnostic tools to infer the properties of the accretion flow (i.e., its density and temperature distributions) at a few thousand Schwarzschild radii from the SMBH (where no current observation can provide a direct estimate). This was done by means of hydrodynamic simulations, of the type performed by our group to study the gas and dust cloud G2 and by a thorough comparison of the resulting observables with available and future observations throughout the electromagnetic spectrum. Of particular interest is the star S2 which recently had its (very well observed) peri-center passage in early 2018. It is found that there will be no observable impact due to the interaction of the wind, unless the atmosphere surrounding Sgr A* would be unrealistically dense. This was later proven by observations. The second project consisted of simulations of clump formation in stellar winds and asks the question whether these allow the formation of G2-like clouds. We find that due to various reasons (stellar orbital constraints, mass spectrum of produced clouds, etc.), this is unlikely. In the third project, we run a simulation including the whole cluster of young stars in the Galactic Center, to understand how the winds from these stars influence the dynamics and thermodynamics of the various gas phases in the innermost region. We are able to reproduce the observed density and temperature distribution and additionally find that a cold disc forms naturally, as recently inferred with the help of ALMA observations.

Publications

• 2018, “3D AMR hydrosimulations of a compactsource scenario for the Galactic Centre cloud G2”, MNRAS, 479, 5288
  Ballone, A.; Schartmann, M.; Burkert, A.; Gillessen, S.; Plewa, P. M.; Genzel, R.; Pfuhl, O.; Eisenhauer, F.; Habibi, M.; Ott, T.; George, E. M.
  
• 2018, “Simulating the pericentre passage of the Galactic centre star S2”, A&A, 616, 8
  Schartmann, M.; Burkert, A.; Ballone, A.
  
• 2018, “The Galactic Centre source G2 was unlikely born in any of the known massive binaries”, MNRAS, 478, 349
  Calderón, D.; Cuadra, J.; Schartmann, M.; Burkert, A.; Plewa, P.; Eisenhauer, F.; Habibi, M.
  
• 2019, “Detection of a Drag Force in G2's Orbit: Measuring the Density of the Accretion Flow onto Sgr A* at 1000 Schwarzschild Radii”, ApJ, 871, 126
  Gillessen, S.; Plewa, P. M.; Widmann, F.; von Fellenberg, S.; Schartmann, M.; Habibi, M.; Jimenez Rosales, A.; Bauböck, M.; Dexter, J.; Gao, F.; Waisberg, I.; Eisenhauer, F.; Pfuhl, O.; Ott, T.; Burkert, A.; de Zeeuw, P. T.; Genzel, R.
  
• 2020, “3D simulations of clump formation in stellar wind collisions”, MNRAS, 91
  Calderón, D.; Cuadra, J.; Schartmann, M.; Burkert, A.; Prieto, J.; Russell, C. M. P.
  
• 2020, “Stellar Winds Pump the Heart of the Milky Way”, ApJ, 888, 2
  Calderón, Diego; Cuadra, Jorge; Schartmann, Marc; Burkert, Andreas; Russell, Christopher M. P.