The investigation by the Laser Interferometer Gravitational-Wave Observatory, or LIGO, and the Virgo Collaboration sets the most stringent limits yet on the amount of gravitational waves – or ripples in the fabric of space and time produced by violent events in the distant universe – that could have come from the Big Bang in the frequency band where LIGO can observe. Analyzing data taken from 2005 to 2007, the scientists have narrowed details of how the universe looked in its earliest moments.
“While the evolution of the universe after it was a few minutes old is well understood, there is little observational data probing the evolution prior to that epoch,” said Marco Cavaglia, assistant professor of physics and astronomy and principal investigator on the UM LIGO Team. “By setting limits on the amount of gravitational waves today, we can compute how much gravitational radiation was present in the past. This gives us information on the characteristics and the evolution of the primordial fluctuations that eventually gave birth to the galaxies we see today.”
The research, which appears in the Aug. 20 issue of the journal Nature, also constrains models of cosmic strings, objects that are purposed to have been left over from the beginning of the universe and subsequently stretched to enormous lengths by the universe’s expansion. The strings, some cosmologists say, can form loops that produce gravitational waves as they oscillate, decay and eventually disappear.
Instruments used to collect the data included the LIGO interferometers, a 2-kilometer and a 4-kilometer detector in Hanford, Wash., and a 4-kilometer instrument in Livingston, La. The Virgo Collaboration, which designed and constructed the 3-kilometer-long Virgo interferometer in Cascina, Italy, is funded by the Centre National de la Recherche Scientifique (France) and by the Istituto Nazionale di Fisica Nucleare (Italy).
“The existence of gravitational waves was predicted by Albert Einstein in 1916 in his general theory of relativity,” Cavaglia said. “The LIGO and GEO600 instruments have been actively searching for the waves since 2002; the Virgo interferometer joined the search in 2007.”
The authors of the new paper report that the probable background of gravitational waves has not been discovered, but the non-discovery of background described already offers its own brand of insight into the universe’s earliest history.
“We now know a bit more about the parameters that describe the evolution of the universe when it was less than one minute old,” said Vuk Mandic, assistant professor at the University of Minnesota. “This result is one of the long-lasting milestones that LIGO was designed to achieve.”
The LIGO Scientific Collaboration is a group of 600 scientists at universities around the United States and in 11 foreign countries. The University of Mississippi is a member of the collaboration’s Compact Binary Coalescence Group, which studies the detection of gravitational waves from the inspiral and merger of binary compact stars and black holes.
The next major milestone for LIGO is the Advanced LIGO Project, slated to begin operation in 2014. Advanced LIGO will incorporate advanced designs and technologies that have been developed by the LIGO Scientific Collaboration. It is supported by the National Science Foundation, with additional contributions from the U.K.’s Science and Technologies Facilities Council and Germany’s Max Planck Society.
The project was designed and is operated by Caltech and the Massachusetts Institute of Technology for the purpose of detecting gravitational waves and for the development of gravitational-wave observations as an astronomical tool.
“With Advanced LIGO, a major upgrade to our instruments, we will be sensitive to sources of extragalactic gravitational waves in a volume of the universe 1,000 times larger than we can see at the present time,” said Jay Marx of the California Institute of Technology, LIGO’s executive director. “This will mean that our sensitivity to gravitational waves from the Big Bang will be improved by orders of magnitude.”