Understanding the physical mechanisms and capabilities of gravitational wave detectors
Open Access
- Author:
- Koop, Michael Jameson
- Graduate Program:
- Physics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 05, 2014
- Committee Members:
- Lee S Finn, Dissertation Advisor/Co-Advisor
Martin Bojowald, Committee Member
Dr Benjamin J Owen, Committee Member
Michael Eracleous, Committee Member - Keywords:
- gravitational waves
general relativity
pulsar timing array
detection
interferometer - Abstract:
- The direct detection of gravitational waves from astrophysical sources has been a goal of physics and astronomy for over 40 years. Two modern techniques for detecting gravitational waves that are actively being pursued are gravitational wave detection via laser interferometry and pulsar timing arrays (PTAs). In this dissertation we address a number of questions regarding how these detectors physically interact with a gravitational wave and how PTAs can be optimized for various scientific goals. We develop a fully physical and gauge-invariant description of the response of a wide class of light travel time gravitational wave detectors (which includes PTAs and laser interferometers) in terms of the spacetime Riemann curvature, the physical quantity that describes all gravitational phenomena in general relativity. In the presence of a gravitational wave with a radiation length-scale that is much shorter than the background curvature length-scale, we find the leading contribution to the detector response is an integral of the gravitational wave curvature along unperturbed photon paths between the detector components. This provides a simple, intuitive understanding of how these detectors operate. This framework also allows the straightforward calculation of corrections to the detector response corresponding to the relative motion of detector components and non-Minkowski background spacetimes. We then focus on gravitational wave detection via pulsar timing and introduce performance metrics that quantify the ability of a PTA to detect isolated gravitational wave signals, measure their radiation polarization, and localize their sources on the sky. The PTA sensitivity depends, in part, on the measured timing noise of each pulsar in the array. The timing noise can be reduced by longer pulsar observation times. Using the NANOGrav PTA as an example case, we identify a set of strategies for the allocation of available telescope time between pulsars that are optimized for various scientific goals. We find that, purely through the reallocation of currently available telescope time, significant improvements in a PTA's performance across a range of criteria can be made over the current practice of allocating equal amounts of time to each pulsar in the array.