Only indirect evidence for black holes exists so far, but someday scientists will be able to detect them, possibly with a little help of a device in a little-known room tucked away in the University of Wisconsin-Milwaukee Physics Building.

The door is labeled “Center for Gravitation and Cosmology Parallel Computation Facility.” One can hear a hum from inside: that of 300 computer nodes, linked together, shelved wall to wall, waiting for a sign.

This computer cluster, named Medusa, is one of many systems analyzing data from instruments far away from this campus via the Internet.

The center is working with universities and institutes across the world as part of the LIGO Scientific Collaboration (LSC). Participants analyze data from the Laser Interferometer Gravitational Wave Observatory (LIGO), which has gravitational wave detectors.

A gravitational wave has not been found yet, but with meticulous filtration of other data the detectors pick up, one will show up eventually. Once gravitational waves are detected, scientists will be able to find existing black holes, among other things.

Gravitational waves are described as “ripples in the fabric of space and time.”

Another analogy was given by post-doctorate student and research associate Xavier Siemens. He said that while an electromagnetic wave, such as light, comes from shaking an electron, a gravitational wave comes from shaking a mass.

Since the waves are very weak, they are not caused by anything around the neighborhood, but by astrophysical events in the distant universe — events such exploding stars and colliding black holes.

This is why the three LIGO detectors are so large. The site in Livingston, La., has a detector with 2.5-mile arms, shaped in an L. There is one of the same size in Hanford, Wash., along with a second detector, this one with 1.25-mile arms.

Professor Jolien Creighton described a detector in this way: A laser is split into two beams — one travels back and forth through one arm; the other bounces back and forth through the second arm. After traveling through the arms, the beams return to the beam splitter and recombine, canceling each other out.

If a gravitational wave were to pass through, one arm would grow longer and the other shorter, so some light would not cancel. The challenge is that other “noise” such as seismic activity (ground motion), also shows up.

So far, a gravitational wave has not been confirmed because a signal has not been strong enough compared with the noise.

Medusa is still humming though, and the members of the UWM LSC group are keeping up with it, studying its data for a sure sign.

The system, commissioned in 2001, will soon to be replaced by a better worker, Nemo. This cluster will be at least 10 times more powerful and will probably be installed in late December. Nemo is mostly funded by the National Science Foundation, which provided more than $1.4 million.

Professor Bruce Allen said he feels privileged to create and use Nemo, one of the most powerful systems used to analyze gravitational wave signals.

“I am interested in doing this because Nemo is part of an international collaboration,” he said. “For being small and not that well-known for research, UWM has proven to be good enough to get funding.”

Although UWM will play a significant role in LIGO, all national participants and international collaborators will be needed to confirm a wave has been detected.

“We would want to see it in several detectors to exclude the possibility that is noise, some artifact or of other terrestrial origin,” Creighton said. “Correlating it with an event in the sky, such as a gamma-ray burst, would be great too.”

When that day does come, Albert Einstein will be proven right: the waves exist. That is just the beginning.

“It opens up a whole new window to study the universe with,” Siemens said. “Just like you can see things with x-rays you don’t see in optical wavelengths, we should be able to see things in the gravitational spectrum we don’t see in the electromagnetic spectrum.”

Gravitational waves will reveal cosmic furies such as black holes swallowing neutron stars and star quakes in neutron stars.

Someday, gravitational wave detectors may reveal the stochastic background, or the sum of all remnant gravitational waves in the universe. This would allow scientists to observe the universe at times earlier then they can observe it with light, peering into its beginnings.

Finding a wave is not just a matter of time, but technology. In 2008 the LIGO instruments will begin to be upgraded so they will be 10 times more sensitive. Creighton said there is a high certainty that waves will then be detected on a daily basis.

Thanks to a project led by Allen at UWM, any computer owner around the world can assist in searching the sky along with the LSC. By going to http://einstein.phys.uwm.edu, you can download software that will allow your computer to analyze data from LIGO and GEO 600 in Germany during its idle time.

Your computer, then, can be waiting too.

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