Karan Jani - Undergraduate Student
Choosing The Initial LISA Orbital Configuration
My research with Prof. Finn is mainly focused on the Laser Interferometer Space Antenna (LISA) mission. It proposes to detect the gravitational radiation by synthesizing one or more interferometric gravitational wave detectors from fringe velocity measurements generated by changes in the light travel time between three spacecraft in a special set of drag-free, circumsolar orbits. Once the spacecraft are set into their orbits, the orientation of the LISA interferometers at any further time is fixed by the Kepler Laws and the initial orientation of the spacecraft constellation. The initial orientation does not affect those locations on the sky where LISA has greatest sensitivity to gravitational waves; however, it does affect those locations where nulls in the LISA response to gravitational waves fall. By artful choice of the LISA initial orientation we can thus choose to optimize LISA's sensitivity to sources or groups of sources whose location (eg. the galactic center or plane, nearby globular cluster, etc.) may be known in advance.
Testing The "No-Hair" Theorem Using S-stars
In collaboration with Dr. Stanislav Babak at the Max Planck Institute for Gravitational Physics (Potsdam), I am working on the astrophysical tests for the "no-hair" theorem of General Relativity. "No-hair" demands that the mass (M) and spin (J) of a blackhole (BH) are related to its quadruple moment as Q^2 = -J^2/M. This theorem can be tested by measuring the orbital precessions, caused due to the relativistic effects, of the star orbiting a BH. The recently observed young OB-type stars, called the S-stars, near Sgr A* gets as close as around 200 AU from the central object - believed to be a Super Massive BH (SMBH). Astrometric observations of these S-stars have provided an accurate prediction on SMBH's Keplerian mass. By measuring the relativistic perturbations caused on this stars during their perihelion transit, in principle, one can measure J and Q2 of SMBH uniquely. For a more realistic calculation though, one has to take into account the secular Newtonian perturbations that other stellar objects in that regime causes on the S-stars and compare this with the measured relativistic effects. Some parameters of S-stars motion, such as period, eccentricity and orientation angles, can also drastically influence the orbital precession (eg. with Kozai mechanism). Our study is focused on investigating such effects and checking whether a clean test of no-hair is possible.
The image for S-stars is taken from: The September, 21, 2000 issue of NATURE magazine "The Accelerations of Stars Orbiting the Milky Way's Central Black Hole" by A. M. Ghez, M. Morris, E. E. Becklin, A. Tanner, & T. Kremenek