Testing General Relativity with Infrared Interferometry of the Massive Black Hole in the Galactic Center: An Homage to Charles Hard Townes

Monday, September 11, 2017 - 4:15pm
Room #1 LeConte Hall
UC Berkeley
Public Lecture: 

When Nobel Laureate Charles Townes joined the UCB Physics Department in the late 1960s he started a series of highly innovative, and later world-famous experimental astrophysics projects. He and his students developed novel infrared spectrometers and discovered from Doppler motions of ionized gas the first evidence for a compact mass in the Galactic Center, SgrA*, which he proposed to be a massive black hole of about 3 million solar masses. He also pioneered infrared spatial interferometry to realize angular resolutions much greater than achievable with single optical telescopes. One of his (unfulfilled) dreams was to use this new technique for studying SgrA* in detail.

Now, fourty years later, we have robust evidence, from detailed astrometric imaging and Doppler spectroscopy of stars orbiting SgrA* that Charlie's proposal indeed was correct. After 10 years of development, a group of us in Europe led by Frank Eisenhauer at MPE last year put into operation a novel near-infrared interferometric imager/spectrometer, GRAVITY. This instrument combines the light of all four 8m telescopes of the Very Large Telescope of the European Southern Observatory in Chile, for a 'super-telescope' of 130m equivalent diameter.

It is a great pleasure to report that after the first season of observing with GRAVITY, about two years after Charlie's passing, we have managed to realize his dream of imaging SgrA* will milli-arcsecond resolution. With a sensitivity more than a hundred times better than previous infrared interferometers, we are now on our way to test General Relativity for the first time around a million solar mass, black hole, as one of the orbiting stars is getting read to reach its peri-bothron of 17 light hours in summer of 2018.