Ready,
detect, LIGO
Armed with
one of the most advanced scientific instruments of all time, physicists
are now intently watching the universe for the first evidence of gravitational
waves. First predicted by Albert Einstein in 1916 as a consequence of
his 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. The first 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 its sensitivity are coming very rapidly, as
the final interferometer systems are implemented and the sources of noise
are uncovered and their potentially limiting effects are 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. In Hannover, Germany, meanwhile, a similar device
(a German/U.K. collaboration known as GEO) is also getting under way,
and those instruments are being used together as the initial steps in
building a worldwide network of gravitational-wave detectors.
The first
data were recorded during a 17-day data run in September 2002. Those data
have now been analyzed for the presence of gravitational waves, and the
results were presented at the American Physical Society meeting in Philadelphia
earlier this month. 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, were reported.
Although detections are realistically not expected at LIGO’s present
sensitivities, a second data run is now under way employing 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 in sensitivity
of a future LIGO 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 a collaboration between Caltech
and MIT was responsible for its construction. A scientific community consisting
of more than 400 scientists from around the world is now involved in research
at LIGO.
For further
information, visit the main LIGO website at http://www.ligo.caltech.edu.
More information on the LIGO collaboration is at http://www.ligo.org.
Additional information on the MIT collaboration is at http://space.mit.edu/LIGO/.
The GEO website is at http://www.geo600.uni-hannover.de/.
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