| Research | ||||||||||||||||||||
|
Quick LinksMy ResearchMy research interests primarily lie in theoretical astrophysics, relativity, and cosmology. I am especically interested in the emerging field of gravitational wave astronomy and what it will tell us about the "dark side of the universe." I am interested in issues related to the modeling and detection of sources of gravitational waves, the physics of compact objects (neutron stars, white dwarfs & black holes), and the nature of dark matter and dark energy.[ I am a graduate student in the Department of Astronomy at Cornell University. I recieved my Bachelor's degree in physics from Caltech in June 2000. My thesis advisor is Eanna Flanagan. ] Here is a description of some of the research problems I have worked on: 1. The Gravitational Radiation Rocket Effect, (with Scott Hughes,Daniel Holz, David Merritt, & Milos Milosavljevic) As the two holes inspiral and merge, the linear momentum leaving the system in gravitational radiation imparts a "kick" or recoil to the center of mass of the binary. This is called the gravitational "radiation rocket" effect.The resulting kick has the potential to be quite large, > 1000 km/s (which is larger than the escape velocity of most large galaxies), but we have shown that is likely much smaller than this. The effect is still potentially important for astrophysical systems that involve black hole mergers -- these may occur at the centers of galaxies or globular clusters, or in dark matter halos in the early universe. If the recoil exceeds the escape velocity of the host system it may eject the merged black hole binary completey. In cases where the kick velocity is not as large it could displace the black hole, which could also have observable effects. [See links to papers below.] 2. Crushing Neutron Stars Several years ago numerical simulations of binary neutron stars by Wilson, Mathews, and Marronetti showed a surprising result: Neutron stars that are ordinarily stable collapse to black holes when they are placed in a binary. This is called "binary-induced collapse" or "star crushing". This result was very controversial and led to over 15 papers countering the claims of collapse. Determining if this effect is real is important becuase it would affect our ability to detect the gravitational waves from these systems with LIGO and other detectors. After correcting an error found in their equations by Eanna Flanagan, Wilson and Mathews found that the stars in their simulation were not compressed as much as before. But some small compression still remained. Is this remaining compression due to some other error in their code or is it a real physical effect? Kip Thorne suggested that I look at this issue as a senior project some years ago (I don't want to say how many). Since its tricky to try to explain the puzzling result of someone's computer code, the goal is instead to answer the following general question: Is there any way to compress (or crush!) a neutron star through tidal gravitational interations. It turns out that you can get a compressional force when a the fluid in the neutron star interacts with a gravitomagnetic field. A gravitomagnetic field is a general-relativistic piece of the gravitational field that is similar to the magnetic field that we are all familiar with. Just as a magnetic field is generated by moving charges or electric currents, the gravitomagnetic field is generated the motion of masses, such as the rotation of the Earth or the orbital motion of two neutron stars in a binary. If the fluid in the neutron star has a certain velocity pattern, the fluid motion will couple to the gravitomagnetic field to produce a compressive force. Whether or not a compression of the star actually results depends on if this fluid velocity is already present or if it must be induced by the gravitomagnetic field. In any case, the total compression possible is usually small, but could be big for stars that are close to their maximum mass (these are stars that are close to being unstable and are easily compressed). 3. Localization Invariance of Tidal Work As an undergraduate summer project (SURF) in 1999, I worked with Kip Thorne on a project related to tidal work. This was motivated by the Wilson-Mathews simulations discussed above. It concerned the definition of the energy that's transfered through the tidal interaction of two gravitating bodies [such a transfer occurs, for example, between Jupiter and its highly volcanic moon, Io]. Because it's tricky to define things like energy in general relativity, it seemed as if an ambiguity existed in the formula used to describe this interaction. I bascially showed that there is no ambiguity. [Patricia Purdue, Ivan Booth, and Jolien Creighton also have papers that address this issue, but use a different approach.] Publications
All papers on ADS All papers on SPIRES-HEP Conference Talks[The following are conferences at which I've given a talk. Some of the results presented in those talks were rather preliminary and have since changed. You should consult the published papers for the accurate information.]
Notes n' Stuff
Gravitational Wave Links
Relativity Links
Resources on Radiation Reaction & other Gravitational Wave Issues
Relativity Research Groups
Astrophysics Links[page under construction] [last updated 10/23/05] | |||||||||||||||||||
