PhD Thesis

Searching for Gravitational Radiation from Binary Black Hole MACHOs in the Galactic Halo

• Version 0: Original version submitted to UWM Graduate School [PDF]
• Version 1: Version submitted to gr-qc, several typos fixed [PDF]

Abstract

The Laser Interferometer Gravitational Wave Observatory (LIGO) is one of a new generation of detectors of gravitational radiation. The existence of gravitational radiation was first predicted by Einstein in 1916, however gravitational waves have not yet been directly observed.

One source of gravitation radiation is binary inspiral. Two compact bodies orbiting each other, such as a pair of black holes, lose energy to gravitational radiation. As the system loses energy the bodies spiral towards each other. This causes their orbital speed and the amount of gravitational radiation to increase, producing a characteristic ``chirp'' waveform in the LIGO sensitive band.

In this thesis, matched filtering of LIGO science data is used to search for low mass binary systems in the halo of dark matter surrounding the Milky Way. Observations of gravitational microlensing events of stars in the Large Magellanic Cloud suggest that some fraction of the dark matter in the halo may be in the form of Massive Astrophysical Compact Halo Objects (MACHOs). It has been proposed that low mass black holes formed in the early universe may be a component of the MACHO population; some fraction of these black hole MACHOs will be in binary systems and detectable by LIGO.

The inspiral from a MACHO binary composed of two 0.5 solar mass black holes enters the LIGO sensitive band around 40 Hz. The chirp signal increases in amplitude and frequency, sweeping through the sensitive band to 4400 Hz in 140 seconds. By using evidence from microlensing events and theoretical predictions of the population an upper limit is placed on the rate of black hole MACHO inspirals in the galactic halo.

Results

The results of my thesis are contained in the LSC publication:

Search for Gravitational Waves from Primordial Black Hole Binary Coalescences in the Galactic Halo (B. Abbott, et. al.)

Errata

Fixed from version 0 to version 1

1. Fixed the title: added the missing word 'binary.'
2. Fixed typo in Eq. (2.108) for F_+.
3. Fixed typo in the definition of orbital phase, Eq. (2.104)
4. Added text which explains why Eq. (2.124) which defines \tilde{h}(f) contains the distance dependent amplitude factor.
5. Fixed typo in Eq. (4.3) which defines effective distance.