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Gravitational Waves

Gravitational waves (GWs) are distortions in the fabric of space and time, predicted by Einstein's General Theory of Relativity, which travel at the speed of light. They are generated by rapid movements of massive objects, such as black holes and/or neutron stars in close binary orbits, supernova explosions, rapidly spinning deformed neutron stars, and the extreme conditions in the early universe shortly after the Big Bang. While the effects of GWs have been observed, the waves themselves have not yet been detected. An international network of detectors has recently been constructed which is expected to make the first detection of gravitational waves and allow us to observe the universe with gravitons as well as photons. This network includes the Laser Interferometer Gravitational-Wave Observatory (LIGO), which uses an L-shaped interferometer to measure changes smaller than a proton in the difference between the 2.5-mile lengths of its "arms". RIT researchers work within the LIGO Scientific Collaboration to analyze the data taken by LIGO and other detectors, searching for the signatures of astrophysical systems such as accreting neutron stars and binaries of spinning black holes.

GW animation

The image shows the effects of the gravitational waves generated by a simple system, a binary of two equal masses in a circular orbit around their center of mass. (Upper left; the circular orbit looks elliptical because we are viewing it at a 75-degree angle.) The changes between distances of freely floating objects (lower left) can be resolved into two polarization states, known as "plus" (shown in green) and "cross" (shown in red). The signal in a detector like LIGO will be a combination of these plus and cross waveforms, plus instrumental noise. In a physical system, the gravitational waves will carry away energy, causing the binary orbit to decay and the masses to spiral in towards each other, emitting a "chirp"-like waveform.

LIGO and other ground-based detectors are sensitive to GWs with frequencies above a few tens of hertz. An envisioned future generation of low-temperature, underground interferometers may manage to reach down to a few hertz or so. To view very massive GW sources, such as mergers of the supermassive black holes (which reside at the core of most galaxies), or "guaranteed" sources such as white dwarf binaries seen in our galaxy, we must go down to millihertz frequencies, for which we need a space-based GW detector. Such a detector, known as the Laser Interferometer Space Antenna (LISA), has been planned for many years; its current incarnation is as a European Space Agency mission known as eLISA/NGO.

By viewing the universe in GWs, we will be able to directly observe events like black hole collisions that are hidden from conventional electromagnetic-based (e.g. optical orradio) astronomy. In addition, if past experience with infrared, radio wave, and gamma-ray astronomy give us an indication of what to expect when we open this new gravitational-wave window onto the universe, there may be many surprising new discoveries waiting to be made. Scenarios that we have yet to imagine could be the most energetic sources of GWs. The direct observation of GWs itself will be one of the greatest discoveries of fundamental physics of the 21st century. A Nobel Prize was already awarded in this field, in 1993; a new Nobel Prize is expected within the next few years for the direct detection of GWs.  

One of the CCRG research focus is on GW data analysis and its interplay with astrophysical source simulation, e.g. how the results of source simulations of compact objects can be used to design data analyses that extract relevant information from GW detectors.

John Whelan (lead), Melissa Frei Prabath Peiris, Anthony Castiglia, Hiroyuki Nakano, Carlos Lousto, Manuela Campanelli, Hans-Peter Bischof.

NSF (PHY-0855494,PHY-1207010)

External Collaborations:

  • The Ligo Scientific Collaboration (LSC) – A well‐organized collaboration of approximately 760 scientists worldwide who have joined together in the search for gravitational waves from the most violent events in the universe, such as the merger of black holes and neutron stars, the explosion of supernovae and the Big‐Bang.
  • The LISA international Science Community (LISC) – eLISA/NGO is a planned ESA space‐based gravitational‐wave observatory that would allow us to detect gravitational waves from massive black‐hole mergers in the centers of galaxies, from the ultra‐compact binary systems in our own Galaxy and from many other sources. The purpose of LISC is to exchange information about LISA with the wider science community.
  • The LCGT and DECIGO collaborations– These are Japanese ground‐based and space
    gravitational wave antenna projects.
  • The Ninja Project – The goal of the Numerical Injection Analysis (NINJA) project is to bring the numerical relativity and data analysis communities together to pursue projects of common interest in the areas of gravitational‐wave detection, astrophysics and astronomy.