When Einstein published the special theory of relativity a century ago, it signaled the start of his decade long quest to develop a theory of gravitation that was consistent with his newly developed insights into space and time. It is now more than 90 years since Einstein first wrote the field equations of general relativity and revolutionized our understanding of gravitation. Since then, the theory has passed every experimental test to date and has provided both dramatic predictions and explanations of physical phenomena in the Universe.
One of these predictions are gravitational waves, ripples in space-time caused by objects whose motion is accelerated and not perfectly spherically symmetric. Supernovae, gamma ray bursts and compact binary systems are amongst the expected main sources of gravitational waves. The first experimental evidence, albeit indirect, come in 1979 from the study of a binary pulsar by Hulse and Taylor.
Detection of gravitational waves will certainly open a new window to the universe. As it happened with the first infrared or X-ray observations, gravitational wave data could reveal all kind of new and unsuspected phenomena. As opposed to electromagnetic radiation, gravitational waves can pass through any matter without being affected and they can be used to probe objects almost invisible any other way, like black holes and neutron stars. Also, the cosmic gravitational wave background, produced earlier than the microwave one, will provide us with a new way to study the earlier universe.
The Laser Interferometer Gravitational-Wave Observatory (LIGO) is an ambitious project aimed to detect gravitational waves from astrophysical sources. LIGO began its search in 2002, making use of state-of-the-art technology. This year it will start a new science run (S6) with enhanced instruments, operating at unprecedented sensitivities. LIGO has achieved a critical point where the astronomy community eagerly awaits the first detection and the beginning of the new field of gravitational-wave astronomy.
In 2004, the National Science Board reaffirmed its long-term commitment to gravitational wave astrophysics by approving the Advanced LIGO upgrade to the interferometers. These improvements, when fully implemented in 2014, will render the Advanced LIGO detectors ten times more sensitive than the initial ones. This should bring LIGO into an era of routine astronomical observations.
The inspiral and merger of a compact binary system generates gravitational waves which sweep upward in frequency and amplitude through the sensitive band of the Earth-based detectors. The detection of gravitational waves from these astrophysical sources will provide a great deal of information about strong field gravity, dense matter, and the populations of neutron stars and black holes in the Universe. Patrick Brady co-chairs the inspiral analysis group of the LIGO Scientific Collaboration. This working group's goal is to identify gravitational-wave signals from compact binary sources in the detector data, and estimate the waveform parameters. To date, no gravitational waves have been identified from these sources, so the scientific product of the group is to place limits on the coalescence rate of binaries in the Universe. When wave are detected, it will be possible to infer information about the binary populations, and possibly probe the disruption of neutron stars, test alternative theories of gravity, and bound the mass of the graviton. These are just some of the ideas for gravitational-wave astronomy and physics with these sources.
Maria Alessandra Papa co-chairs the pulsar group of the LIGO Scientific Collaboration. This working group's goal is to identify gravitational-wave signals which last for long times relative to the observing time. The archtypical gravitational-wave source is a rapidly rotating neutron star. These objects are already observed using radio telescopes, but the gravitational waves carry a host of new information about the structure of the neutron stars. Moreover, not all rapidly rotating neutron stars will be pulsars. This means that gravitational waves provides an new way to find these objects in our Galaxy. Since the search methods are not tied particularly to pulsars, there may be unexpected sources which continuously emit gravitational waves.
Commodity cluster computing has become a standard method of achieving high performance at low cost. Bruce Allen built the first Beowulf cluster at UWM in 1998 with the help of (then postdoc) Warren Anderson. In 2001, the group added a 300-node state of the art cluster (Medusa) designed for fast-turnaround and prototyping data analysis. This cluster served as a pathfinder in the LSC deploying Condor and distributing data across the cluster using cheap commodity hard disks to achieve 24 Tbytes of storage. In 2004, the group was awarded a National Science Foundation award to build a new cluster called Nemo, deployed in 2006.
