By Sabrina Zearott, Department of Physics and Astronomy
 
PULLMAN, Wash. — Partnership in a NASA grant will allow a Washington State University researcher to work on predictions and simulations concerning space waves and warps.
 
Black holes in space have such strong gravity that even light cannot escape. When they collide, they merge and form an even bigger black hole. The merger violently distorts space, sending out strong ripples in all directions.
 
These “gravitational waves” can be measured on Earth to provide clues to how physics works under high-gravity conditions, said Matthew Duez, assistant professor in Washington State University’s Department of Physics and Astronomy since fall 2010.
 
Mergers between black holes, neutron stars (collapsed remnants of aged stars), or a black hole and a neutron star give off specific, predictable gravitational wave patterns. This is similar to the expected V-shaped ripples from a boat on a river or the series of circles from a rock dropped in the water.
 
To predict these patterns, Duez is using computer models that he developed with his colleagues at the Caltech-Cornell Simulating eXtreme Spacetimes Project (SXS).
The SXS collaboration is one of the leading groups in this field and has seen its share of challenges: initially, simulations turned into nonsense due to small, rapidly multiplying errors. That problem has been fixed by changing the method of solving Einstein’s equations, but the simulations remain complicated and require a high degree of accuracy.
 
Duez and Caltech professor Christian Ott are applying these predictions and simulations to another type of signal, called a short-duration gamma-ray burst. Satellites detect these bursts almost daily, but scientists have not agreed on their cause. Many believe that some of them result from a black hole shredding a neutron star.
 
Duez and Ott recently received a substantial grant from NASA – about $475,000 for the next three years, half of which goes to WSU – to investigate these signals. Specifically, they are working with NASA and the Laser Interferometer Gravitational Wave Observatory (LIGO) to see if the gravitational wave patterns that accompany short-duration gamma-ray bursts match their predictions for neutron star-black hole mergers.
 
Carrying out these simulations is a step toward creating a catalog of signals from different types of mergers; the catalog would help scientists interpret the gravitational wave signals detected by LIGO. These signals could contain a wealth of knowledge about the makeup of neutron stars, as well as test our understanding of how strong-gravity objects warp space.

Hossein-Nouri Deaton
Two of Duez’s WSU graduate students, Brett Deaton and Fatemeh Hossein-Nouri, are working with him on these questions. Deaton is testing how well LIGO’s detection strategies work in the case of black hole-neutron star merger signals. Hossein-Nouri is studying the aftermath of these mergers: specifically, what happens to the nuclear matter debris left outside a black hole after it shreds a neutron star.