Die größten Schwarzen Löcher am Himmel

• Antragsteller: Professor Dr. Andreas Eckart
• Fachliche Zuordnung: Astrophysik und Astronomie
• Förderung: Förderung von 2019 bis 2022
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 411720221

Zusammenfassung der Projektergebnisse

The center of our Galaxy, the Milky Way, contains one of the most fascinating astrophysical phenomena of the universe. Located at a distance of approximately 28000 light-years from the Solar system it harbors a bright radio source, Sagittarius A* (SgrA*), i.e., in the constellation Sagittarius close to the border to Scorpius. It is almost undisputed that SgrA* is the radiative counterpart of a Super-massive Black Hole (SMBH) with a mass of approximately four million solar masses. Astrophysicists have strong evidence that most regular galaxies contain a SMBH in their corresponding center. Due to its proximity, SgrA* provides us with an unique opportunity to study such an object with the highest obtainable resolution. Investigating SgrA* may thus not only help us to understand the physical processes in the core of our Galaxy, but it might also be a an essential element for a more general understanding of galactic nuclei. SgrA* has first been detected as a steady radio source. Ongoing observations at different wavebands with increasing angular resolution and sensitivity have revealed that in addition to a constant flux density (referred to as the quiescent emission) SgrA* also shows radiation outbursts (referred to as flares) across the entire frequency regime of the electromagnetic spectrum - from the radio to at least the X-ray domain. The investigation of these flares is essential for the understanding of the physical conditions in the immediate vicinity of a SMBH. Most models include some form of synchrotron emission to explain the occurrence of the flares but the exact mechanisms behind X-ray flares are highly disputed. Mainly two concurrent models are currently debated: high energy synchrotron, or synchrotron self- Compton (SSC) emission. Both possible explanations differ significantly in terms of the predicted electron energies and plasma densities. Using submillimeter (sub-mm) data obtained with the LArge BOlometer CAmera (LABOCA), mounted at the Atacama Pathfinder EXperiment (APEX) telescope, and radio data from the Australia Telescope Compact Array (ATCA), as well as X-ray data from the Chandra X-ray Observatory (CXO) obtained during the X-ray Visionary Project (XVP) campaign, we have performed an analytical and statistical investigation of the flare light curves. In the case of the X-ray data the analytical challenge is that X-ray light curves are subject to instrumental pile-up phenomena and low count rate Poisson statistics. We developed and used a count rate distribution fitting routine, which is based on Approximate Bayesian Computation (ABC). Having developed this fitting routine we were able to describe the X-ray count rate distribution as a power-law with an exponential cutoff and estimate its parameters. Using analytical considerations, we deduce that the X-ray flares are most likely produced by an SSC mechanism. We also investigated the possible relation between the accretion onto SgrA* and an interaction with stellar and dusty objects like the G2/DSO, that had its closest approach to SgrA* in spring 2014. It has been speculated whether this flyby might lead to an increased accretion rate onto SgrA* and therefore to increased flaring activity. Our data rules out that such an increase occurred at least up to 2017. The statistical analyses reveal, that the observed light curves of SgrA* at different wavebands are fully compatible with the following emission model: adiabatically expanding synchrotron blobs are the origin of the observed radio to NIR flares. The X-ray flares are most probably produced by an SSC mechanism. We also compared the properties of accretion and emission phenomena between SgrA* and other more massive Super Massive Black Holes.

Projektbezogene Publikationen (Auswahl)

• 2020, ApJ 896, 100; Kinematic Structure of the Galactic Center S Cluster
  Ali, Basel; Paul, Daria; Eckart, Andreas ... Matthias Subroweit ...
  
• 2020, ApJ 898, 138; Synchrotron Self-Compton Scattering in SgrA* Derived from NIR and X-Ray Flare Statistics
  Subroweit, Matthias; Mossoux, Enmanuelle; Eckart, Andreas
  
• 2021 ApJ 909, 62; First Observed Interaction of the Circumstellar Envelope of an S-star with the Environment of SgrA*
  Peißker, Florian ; Ali, Basel ; Zajacek, Michal ; Eckart, Andreas; Hosseini, S. Elaheh ; Karas, Vladimir ; Clenet, Yann ; Sabha, Nadeen B. ; Labadie, Lucas; Subroweit, Matthias
  
• 2021, ASPC 528, 453; SgrA*’s X-ray and Near-infrared Flare Statistics Point Toward a Synchrotron Self-Compton Nature of Flares
  Subroweit, M.; Eckart, A.
  
• Study of Radiation Outbursts in the Vicinity of a Super-massive Black Hole - Flare Statistics of SgrA*. Diss., Mathematisch-Naturwissenschaftliche Fakultät der Universität zu Köln
  Matthias Subroweit