Scientific Prospects for VLTI in the Galactic Centre: Getting to the Schwarzschild Radius

Paumard, T.; Perrin, G.; Eckart, A.; Genzel, R.; Léna, P.; Schödel, R.; Eisenhauer, F.; Müller, T.; Gillessen, S.
The Power of Optical/IR Interferometry: Recent Scientific Results and 2nd Generation Instrumentation, Eso Astrophysics Symposia. ISBN 978-3-540-74253-1. Springer, 2008, p. 313


The centre of our Galaxy is by far the closest galactic nucleus to theEarth. Not surprisingly, Sgr A*, the super-massive black hole candidate lyingat its gravitational centre, is the black hole (BH) candidate which offersthe best spatial resolution in terms of Schwarzschild radius tpRs, thanksto the good compromise between its mass (≃3.6×106 Msun)and distance (≃8 kpc). For a 3.6×106 Msun BH,tpRs=14 Rsun (≃8 umuas at 8 kpc). This is still twoorders of magnitudes smaller than the spatial resolution offered by theVLTI, but it is the right scale for studies involving only astrometry withPRIMA. We will show how this property can be used to tremendously improvethe knowledge of the central mass distribution, constrain the properties ofthe BH, and even directly probe the space-time around this object.