Source: LSU Department of Communications and University Relations
BATON ROUGE – An investigation by the Laser Interferometer Gravitational-Wave Observatory, or LIGO, Scientific Collaboration and the Virgo Collaboration has significantly advanced our understanding of the early evolution of the universe. Louisiana and LSU have played a very significant role in this worldwide collaboration, which hopes to eventually discover gravitational waves. The results, titled “An Upper Limit on the Amplitude of Stochastic Gravitational-Wave Background of Cosmological Origin,” appeared in the Aug. 20 issue of the prestigious scientific journal, Nature.
Analysis of data taken at the LIGO Livingston and Hanford Observatories over a two-year period from 2005 to 2007 has set the most stringent limits yet on the amount of gravitational waves that could have come from the Big Bang in the gravitational wave frequency band where LIGO can observe. In doing so, the gravitational-wave scientists have put new constraints on the details of how the universe looked in its earliest moments.
This publication marks a major milestone in the decades-long effort to directly detect gravitational waves. The publication of these results shows that all the technical developments that were promised in LIGO’s first phase have actually been achieved. The second phase of the project, Advanced LIGO, is now under way, in which the science team expects to make the first discovery of gravitational waves.
LSU Professor Joseph Giaime is the head of the LIGO Livingston Observatory, and LSU Professor Gabriela Gonzalez is the leader of the detector characterization working group. About 15 other faculty, post-docs and graduate students at LSU are involved in this research.
Much like it produced the cosmic microwave background, the Big Bang is believed to have created a flood of gravitational waves – ripples in the fabric of space and time – that still carry information about the universe as it was immediately after the Big Bang. These waves would be observed as the “stochastic background,” analogous to a superposition of many waves of different sizes and directions on the surface of a pond. The amplitude of this background is directly related to the parameters that govern the behavior of the universe during the first minute after the Big Bang.
Earlier measurements of the cosmic microwave background have placed the most stringent upper limits of the stochastic gravitational wave background at very large distance scales and low frequencies. The new measurements by LIGO directly probe the gravitational wave background in the first minute of its existence, at time scales much shorter than accessible by the cosmic microwave background.
The research also constrains models of cosmic strings, objects that are proposed 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.
Gravitational waves carry with them information about their violent origins and about the nature of gravity that cannot be obtained by conventional astronomical tools. The existence of the waves was predicted by Albert Einstein in 1916 in his general theory of relativity.
The new paper reports that the stochastic background of gravitational waves has not yet been discovered. But the non-discovery of the background described in the Nature paper already offers its own brand of insight into the universe’s earliest history.
“The LIGO detectors have achieved the incredible sensitivity they were designed to have in this phase, due to the hard work of the scientists in the project and in the collaboration, including many LSU professors, students and postdocs,” said Giaime.
The LIGO project, which is funded by the National Science Foundation, or NSF, was designed and is operated by the California Institute of Technology 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.
Research is carried out by the LIGO Scientific Collaboration, a group of 700 scientists at universities around the United States and in 11 foreign countries. The LIGO Scientific Collaboration interferometer network includes the LIGO interferometers and the GEO600 interferometer, which is located near Hannover, Germany, and was designed and operated by scientists from the Max Planck Institute for Gravitational Physics, along with partners in the United Kingdom funded by the Science and Technology Facilities Council, or STFC.
The Virgo Collaboration designed and constructed the 3-km-long Virgo interferometer located in Cascina, Italy, funded by the Centre National de la Recherche Scientifique of France, and by the Istituto Nazionale di Fisica Nucleare of Italy. The Virgo Collaboration consists of 200 scientists from five European countries and operates the Virgo detector. Support for the operation comes from the Dutch–French–Italian European Gravitational Observatory Consortium. The LIGO Scientific Collaboration and Virgo work together to jointly analyze data from the LIGO, Virgo, and GEO interferometers.
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 NSF, with additional contributions from the U.K.’s STFC and Germany's Max Planck Society.
Publish Date:
08-28-2009
