I use gravitational waves and electromagnetic observations to study compact objects, from stellar-mass compact objects in our own Galaxy to supermassive black holes at the centers of distant galaxies.

A list of my publications is available on Inspire and Google Scholar.

Gravitational Wave Detection with Pulsar Timing Arrays

Schematic depiction of a pulsar timing array (J. Hazboun; NASA)

Pulsar timing arrays use millisecond pulsars to detect low-frequency gravitational waves. Gravitational waves induce correlations in the pulse times of arrival of different millisecond pulsars. Pulsar timing arrays are sensitive to gravitational waves emitted by supermassive black hole binaries, which form in galaxy mergers. This includes the stochastic background made up of the incoherent superposition of a cosmological population of supermassive black hole binaries, and individual nearby sources.

I have developed detection techniques for the stochastic background and individual gravitational wave sources. I contributed to the paper placing limits on the stochastic background using the NANOGrav 11-year data set, and I led the paper searching the NANOGrav 11-year data set for gravitational waves from individual supermassive black hole binaries.

Compact Binary Evolution

Artist’s concept of a neutron star accreting material from a red giant (NASA/Dana Berry)

Millisecond pulsars are spun up to their rapid rotation speeds through the accretion of mass from a companion star. Depending on the mass of the donor star, they may have formed in a low-mass X-ray binary (LMXB) or an intermediate-mass X-ray binary (IMXB).

Many millisecond pulsars are found in binaries with a compact object companion, and the mass of the companion can be used to determine whether the millisecond pulsar formed in a LMXB or IMXB. I have used optical and radio observations of binary millisecond pulsars with white dwarf companions to study binary evolution models.