WATCH: CCA Colloquium with Reinhard Genzel

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Title: Testing General Relativity with Infrared Interferometry in the Center of the Milky Way

The Center of our Galaxy is a unique laboratory for exploring the astrophysics around a massive black hole and testing General Relativity in this extreme environment. I will discuss the results of a major campaign of observing the Galactic Center in 2017/2018 with three instruments at the European Southern Observatory’s VLT, including the novel GRAVITY interferometric beam combiner of the 4 UTs.

During this period the B-star S2 completed a peri-passage at ~1400 R_S around the compact radio source SgrA*, and permitted for the first time a test of the equivalence principle and the detection of the first post-Newtonian orbital elements in a classical ‘clock experiment’ around a massive black hole. During bright states (“flares”) we detect centroid motions and polarization changes of the infrared emission of SgrA* itself.

These can be well fitted by near face-on, circular orbits near the innermost circular orbit (ISCO). The mass inferred at ISCO is the same as that within the S2 orbit, further strengthening the evidence that SgrA* is a Kerr black hole.

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