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Feature - Exploring the Gravitational Wave and Grid Universe

Feature: Exploring the Gravitational Wave (and Grid) Universe

Simulated map of upper limits on gravitational wave power reaching the LIGO detectors. Image from S. Ballmer, Class.Quant.Grav. 23 (2006) S179-S186.
(Image Credit Stefan Ballmer)

Scientists have been on the hunt for gravitational waves for over 35 years. Predicted by Einstein in 1916, these waves – ripples in the fabric of space and time – promise to reveal new insight into the birth and evolution of the universe, but have yet to be directly detected.

The largest experiment to date searching for these waves, the Laser Interferometer Gravitational-Wave Observatory, has been on the hunt for the perfect grid for almost a decade.

Searching for gravitational waves is a data- and processing-intensive task. LIGO's three instruments – two in Washington State and one in Louisiana – combine to collect one terabyte of data per day. LIGO researchers comb through this data searching for gravitational waves from a number of sources, including the collisions of black holes and neutron stars and single sources such as pulsars.

“Gravitational waves are very weak signals, and we look for them by comparing the data we collect with what we expect to see,” explains Patrick Brady, LIGO scientist from the University of Wisconsin-Milwaukee. “We use Einstein's theory of general relativity to create these expected signals.”

The large number of possible expected signals, as many as 10,000 for one type of search, makes the hunt computationally intensive. Anticipating such computing needs, in 1997 the LIGO Scientific Collaboration started investigating grid computing, eventually forming the LIGO Data Grid.

“We use the LIGO Data Grid to move all of our scientifically-interesting data from the instruments to the LDG sites,” explains Caltech's Kent Blackburn. “We also use the Virtual Data Toolkit to set up workflows to analyze the data.”

Workflows run on the LDG today, however, run only on the site they were designed for. The LIGO collaboration hopes to move away from this model in the future, and has partnered with the Open Science Grid to explore ways to manage the LDG more efficiently and to integrate the LDG into the greater Grid world.

While LIGO explores its grid possibilities, the hunt for gravitational waves continues. After four years of running, scientists are on the cusp of making their first statements about the birth of the universe as viewed through gravitational waves. Through the stochastic gravitational background, a sea of gravitational waves that permeates the universe, scientists get a glimpse of the distribution of matter and energy throughout the universe.

“Gravitational waves will allow us to see further back in time than any other type of radiation--back to what was happening in the universe a fraction of a second after the Big Bang,” explains Warren Anderson from the University of Wisconsin-Milwaukee.

Theoretical physicists have put forward many explanations of the birth and evolution of the universe, some of which predict different values for this stochastic gravitational background. LIGO can now begin to disprove some of the theories that predict the highest stochastic backgrounds.

Scientists also continue to hunt for the elusive individual gravitational waves from cataclysmic cosmic events such as colliding black holes. Theories predict one gravitational-wave event every 10 years that LIGO, with the help of grid computing, may be able to discover.

“Everyone's crossing their fingers and hoping for a little bit of luck,” adds Blackburn.

Learn more at the LIGO and Open Science Grid Web sites.

-Katie Yurkewicz, iSGTW


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