My Research

Gravitational Waves
Black Holes in the Galactic Center
Recoiling Black Holes
Dark Matter in the Milky Way
First Light











Chandra View of the Galactic Center
Credit: NASA/CXC/MIT/F.K. Baganoff et al.

Black holes in the Galactic Center

In the center of the Milky Way there is a supermassive black hole about four million times more massive than our own Sun. It was first detected as a point like source in radio waves and named Sgr A*. Since then it has been detected in the submillimeter, infrared, and x-ray wavebands. The most interesting and revealing discovery to date, however, has been the motion of young stars around it. Just as the planets move around the Sun, and the Moon around Earth, these stars trace out the gravitational pull of the supermassive black hole revealing its mass and distance.

Surrounding Sgr A* is also a cusp of millions of stars and, we suspect, tens of thousands of smaller, stellar-mass black holes. With Bence Kocsis and Avi Loeb, I determined how these black holes should interact with each other and the stars to form such a cusp if the black holes don't all have exactly the same mass. These stars and black holes zoom by each other, sometimes producing gravitational wave sources and, as I showed with Avi Loeb, othertimes kicking out stars in to the rest of the Milky Way as hypervelocity stars. Hypervelocity stars are stars moving so fast, that they will escape from the gravitational pull of the Milky Way and never return. Their discovery in 2005 by Warren Brown and collaborators has opened a new window into the galactic center, since they likely can only reach such high velocity in the environment of a supermassive black hole like Sgr A* either from stellar mass black holes or when a tight binary is tidally disrupted by the supermassive black hole. Blake Sherwin, with Avi Loeb and me, showed that we might even find hypervelocity stars ejected from our neighbor, the Andromeda Galaxy.

My Relevant Papers

PRODUCTION OF HYPERVELOCITY STARS THROUGH ENCOUNTERS WITH STELLAR-MASS BLACK HOLES IN THE GALACTIC CENTRE.
R. M. O'Leary and A. Loeb. MNRAS, 383:86, January 2008.

HYPERVELOCITY STARS FROM THE ANDROMEDA GALAXY.
B. D. Sherwin, A. Loeb, and R. M. O'Leary. MNRAS, 386:1179, May 2008.

GRAVITATIONAL WAVES FROM SCATTERING OF STELLAR-MASS BLACK HOLES IN GALACTIC NUCLEI.
R. M. O'Leary, B. Kocsis, and A. Loeb. MNRAS, 395:2127, June 2009.