Honorary Fellows: Professor Andrea Mia Ghez
Professor Andrea Mia Ghez for sustained work observing stars close to the centre of our galaxy, determining the existence and mass of the central black hole, and testing elements of Albert Einstein's general theory of relativity.
Professor Andrea Ghez won the 2020 Nobel Prize in Physics (along with Professor Reinhard Genzel) for her demonstration that there is a 4 million solar mass black hole at the centre of our galaxy, as was first postulated by Donald Lynden-Bell and Martin Rees in 1971.
Over 20 years, she tracked the positions of thousands of stars, of which 100 are within the central 1.0 x 1.0 arcsec of the Galactic Centre, and determined the orbits of the closest set of stars. The observations were made in the near infrared (less obscured than the optical), taking out atmospheric turbulence using first the speckle technique and subsequently adaptive optics. This gave the mass of the central object: 4 million solar masses.
Using the Keck Telescope on Mauna Kea and one particular star (known as S0–2) which came within 17 light hours of the black hole, she demonstrated the mass at the centre was so concentrated it had to be a black hole (rather than, say, a spatially extended cluster of stars totalling 4 million solar masses).
She also tested and confirmed the impact of Albert Einstein's general theory of relativity on the observed orbital motion at closest approach.