Armed with one of the most advanced scientific instruments
of all time, physicists are now watching the universe
intently for the first evidence of gravitational waves.
First predicted by Albert Einstein in 1916 as a
consequence of the general theory of relativity,
gravitational waves have never been detected directly.
In Einstein’s theory, alterations in the shape of
concentrations of mass (or energy) have the effect of
warping space-time, thereby causing distortions that
propagate through the universe at the speed of light.
A new generation of detectors, led by the Laser
Interferometer Gravitational-Wave Observatory (LIGO),
is coming into operation and promises sensitivities
that will be capable of detecting a variety of
catastrophic events, such as the gravitational
collapse of stars or the coalescence of compact binary
systems.
The commissioning of LIGO and improvements in the
sensitivity are coming very rapidly, as the final
interferometer systems are implemented and the limiting
noise sources are uncovered and mitigated. In fact,
the commissioning has made such rapid progress that
LIGO is already capable of performing some of the most
sensitive searches ever undertaken for gravitational
waves. A similar device in Hannover, Germany (a
German-U.K. collaboration known as GEO) is also getting
underway, and these instruments are being used together
as the initial steps in building a worldwide network
of gravitational-wave detectors.
The first data was taken during a 17-day data run in
September 2002. That data has now been analyzed for
the presence of gravitational waves, and results are
being presented at the American Physical Society
meeting in Philadelphia. No sources have yet been
detected, but new limits on gravitational radiation
from such sources as binary neutron star inspirals,
selected pulsars in our galaxy and background
radiation from the early universe, are reported.
Realistically, detections are not expected at the
present sensitivities. A second data run is now
underway with significantly better sensitivity, and
further improvements are expected over the next
couple of years.
As the initial LIGO interferometers start to put new
limits on gravitational-wave signals, the LIGO Lab,
the LIGO Scientific Collaboration, and international
partners are proposing an advanced LIGO to improve the
sensitivity by more than a factor of 10 beyond the
goals of the present instrument. It is anticipated that
this new instrument may see gravitational-wave sources
as often as daily, with excellent signal strengths,
allowing details of the waveforms to be read off and
compared with theories of neutron stars, black holes,
and other highly relativistic objects. The improvement
of sensitivity will allow the one-year planned
observation time of the initial LIGO to be equaled in
a matter of hours. The National Science Foundation has
supported LIGO, and collaboration between Caltech and
MIT were responsible for its construction. A scientific
community of more than 400 scientists from around the
world are now involved in research at LIGO.
Related Links
* LIGO
http://www.ligo.caltech.edu
* LIGO’s Collaborators
http://www.ligo.org
* MIT’s LIGO Web Site
http://space.mit.edu/LIGO/
