The Galactic Center Orbits Initiative: Probing the Physics & Astrophysics of the Closest Supermassive Black Hole

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

Our Milky Way galaxy has a supermassive black hole (SMBH) at its center. The investigators have observed individual stars orbiting the SMBH for many years. The investigators use these observations study the effects of strong gravity and the dense environment on these stars. Their observations show the stars moving very fast around the SMBH, as expected. The investigators find the environment near the SMBH is the most extreme of the natural world that can be studied by observations from Earth. These observations, combined with models, are used as a laboratory for understanding the physical principles that govern our universe. The investigators plan further observations using the world's largest telescopes to search for new properties of gravity that can only be detected in extreme environments. Using precise measurements of the stars' motions, the investigators have determined the size and the distance of the SMBH. So far, their observations are exactly consistent with predictions of Einstein's general theory of relativity. The aim of their new project is to refine their tests of relativity by continued monitoring of the motions of stars around the SMBH. They carefully measure how much the stars' positions will stray from the classical description of their orbits. They will more precisely measure the distance to the Galactic center, which sets the size scale of the Galaxy. Furthermore, they expect the densely packed stars at the Galactic center to become joined as binary stars that could ultimately merge with each other to produce new kinds of stars. Some can ultimately become star-sized black holes. The investigators convey to the public the exciting results of their research and attract young people, particularly women, into careers in science and technology. The objectives of this project are based on precise determinations of the orbits of numerous stars located as close to the black hole as possible. Because the density of stars at the Galactic center is exceptionally high, observations with the highest possible spatial resolution are essential. This project will employ adaptive optics with 10m telescopes at the W.M. Keck Observatory. Although the investigators have already obtained many years of data, this is a long-term project because the periods of the orbits range from tens to hundreds of years. Each additional year of data increases the accuracy of the orbits disproportionately because of the constantly improving observational technologies. The orbits will also be used to set strong limits on, or possibly measure, the abundance and distribution of dark matter around the black hole. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.