My Research

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










The gravitational waves created during the inspiral of two black holes
Credit: C. Henze / NASA

Gravitational Waves

Gravitational waves are ripples in space and time produced by the bulk acceleration of matter. They are a prediction of Einstein's General Relativity and are very different from gravity waves (i.e., the ripples in water on the surface of a pond). The existence and detection of gravitational waves have a long and tumultuous history, even pitting Albert Einstein against one of the most reputable journals in the United States. Gravitational waves carry energy and momentum and have indirectly been detected through the decay in the orbit of the famous Hulse-Taylor binary pulsar, earning the discoverers Hulse and Taylor a Nobel Prize in Physics in 1993.

One of the best sources of gravitational waves is the merger of two black holes, which are often the most energetic events in the Universe. Nevertheless, the changes in distance and time a passing gravitational wave induces. The billion dollar LIGO detectors hope to detect changes in distance of order one in 1023. This is comparable to the ratio of distances a person causes the entire Earth to move when she jumps!

My work has so far has focused on sources of gravitational waves detectable by LIGO and other ground-based gravitational wave detectors. I have shown with Bence Kocsis and Avi Loeb that there is a class of eccentric mergers that occur in the centers of galaxies. Because they are eccentric these mergers are distinguishable from nearly all other mergers of black holes in the universe. We also analyzed the gravitational wave signatures of eccentric mergers and showed that they are detectable to greater distances and over longer periods of times than traditional sources. At Northwestern with Fred Rasio and collaborators, I looked at the merger of black holes in dense star clusters. Here black holes sink to the center of the cluster and form tight binaries. We showed when these binaries merge they are almost always circular and that Advanced LIGO is likely to detects tens of these events every year. In addition we looked at how these black holes may occasionally merge to form ever larger black holes, eventually forming intermediate mass black holes. We showed that for realistic recoil velocities, these black holes are more than likely ejected from the cluster before this can happen.

My Relevant Papers

STAR CLUSTERS AROUND RECOILED BLACK HOLES IN THE MILKY WAY HALO : N-BODY SIMULATIONS AND A CANDIDATE SEARCH THROUGH THE SDSS.
R. M. O'Leary and A. Loeb. MNRAS, 421:2737, April 2012.

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.

STAR CLUSTERS AROUND RECOILED BLACK HOLES IN THE MILKY WAY HALO.
R. M. O'Leary and A. Loeb. MNRAS, 395:781, May 2009.

DYNAMICAL INTERACTIONS AND THE BLACK-HOLE MERGER RATE OF THE UNIVERSE.
R. M. O'Leary, R. O'Shaughnessy, and F. A. Rasio. Phys. Rev. D., 76(6):061504, September 2007.

BINARY MERGERS AND GROWTH OF BLACK HOLES IN DENSE STAR CLUSTERS.
R. M. O'Leary, F. A. Rasio, J. M. Fregeau, N. Ivanova, and R. O'Shaughnessy. ApJ, 637:937, February 2006.