Final Report Summary - PROGRESO (Probing General Relativity with Stellar Orbits)
This grant proposal, PROGRESO, aimed at detecting relativistic effects in the stellar orbits around the massive black hole
in the Galactic Center, and in the motions of hot spots close to the event horizon. The main novel data source was the next-generation
instrument GRAVITY for ESO's Very Large Telescope Interferometer. The data will be used in conjunction with a long-term data set
collected at ESO telescope since 1992.
Scientifically, we started testing gravity in a so far unprobed regime of mass and space-time curvature. The Galactic Center
is a uniquely accessible laboratory for gravitational physics, being the location of the closest massive black hole.
Given the mass ratio of 10^−5 between the stars and the black hole, the stars are ideal test particles for the potential in
which they move. Thus the keys to directly probing the gravitational potential are ultra-precise astrometric
measurements of stellar positions and accurately determined radial velocities of the stars.
Two results to which PROGRESO contributed are outstanding: We detected the gravitational redshift from the massive black hole acting on the light of the star S2 as it reached its point of closest approach to the black hole in May 2018. And we have seen that the flaring emission from the black hole itself is moving in a circular way, tracing an orbit at roughly 4 times the size of the black hole and constraining the system's orientation to be almost face-on. The key to success in both cases was the new instrument GRAVITY. PROGRESO contributed the design and implementation of the instrument's metrology system.
in the Galactic Center, and in the motions of hot spots close to the event horizon. The main novel data source was the next-generation
instrument GRAVITY for ESO's Very Large Telescope Interferometer. The data will be used in conjunction with a long-term data set
collected at ESO telescope since 1992.
Scientifically, we started testing gravity in a so far unprobed regime of mass and space-time curvature. The Galactic Center
is a uniquely accessible laboratory for gravitational physics, being the location of the closest massive black hole.
Given the mass ratio of 10^−5 between the stars and the black hole, the stars are ideal test particles for the potential in
which they move. Thus the keys to directly probing the gravitational potential are ultra-precise astrometric
measurements of stellar positions and accurately determined radial velocities of the stars.
Two results to which PROGRESO contributed are outstanding: We detected the gravitational redshift from the massive black hole acting on the light of the star S2 as it reached its point of closest approach to the black hole in May 2018. And we have seen that the flaring emission from the black hole itself is moving in a circular way, tracing an orbit at roughly 4 times the size of the black hole and constraining the system's orientation to be almost face-on. The key to success in both cases was the new instrument GRAVITY. PROGRESO contributed the design and implementation of the instrument's metrology system.