Andreas Eckart: The Galactic Centre Black Hole

• High resolution VLBI observations of Sagittarius A*
• Variable emission of Sagittarius A*
• Nuclear Star Cluster (NSC)
• Gas dynamics at the GC

A standard paradigm in modern astrophysics is that every galaxy with a nuclear bulge harbors a super-massive black hole (SMBH). Furthermore, observations in the past decade have revealed the existence of so-called nuclear star clusters (NSCs) of 10⁵ to 10⁷ solar masses that surround the SMBHs at the dynamical centers of spiral galaxies. The Galactic center (GC) plays a fundamental role in this research because it is ~100 times closer than the next comparable Galactic nucleus (Andromeda Galaxy) and ~1000 times closer than the next active nucleus. This allows us to study the physical processes around an SMBH at an extremely high spatial resolution that is not achievable in any other system. Observations of stellar dynamics in the GC combined with radio-interferometric observations have not only provided the currently best evidence for the existence of SMBHs but have also made it possible to measure the mass of the Galaxy's central black hole, Sagittarius A*, with high precision.



Current GC research topics are closely interrelated.

For example:

Stellar dynamics probe both the mass of Sagittarius A* and of the nuclear star cluster itself. Activity of Sagittarius A* can - and must - be observed simultaneously at X-ray, radio, mm, and near-infrared wavelengths. In order to understand gas dynamics and search for a postulated outflow from Sagittarius A*, one needs to combine near-infrared and radio observations as well as have a profound knowledge of the stellar and gas dynamics within a few pc of the SMBH. The Galactic Center is thus a laboratory for fundamental astrophysics of galactic nuclei