An analysis by the international LIGO (Laser Interferometer Gravitational-Wave Observatory) Scientific Collaboration, including University of Wisconsin-Milwaukee (UWM) scientists, has excluded one previously leading explanation for the origin of an intense gamma-ray burst that occurred last winter. Gamma ray bursts (GRBs) are among the most violent and energetic events in the universe and scientists have only recently begun to understand their origins.

Nick Fotopoulos, a graduate student working in the LIGO Group at UWM, conducted significant parts of the analysis using the UWM Nemo supercomputer cluster under the guidance of Professors Patrick Brady and Jolien Creighton.

This marks the first time scientists involved with LIGO have made a significant contribution to the understanding of such a cosmic event by searching for gravitational waves.

The LIGO observatories, which are funded by the National Science Foundation, are designed to detect gravitational waves produced when massive objects in space move violently. The waves carry the imprint of the events that cause them. The observatories are operated by the California Institute of Technology and the Massachusetts Institute of Technology (MIT), but related research is carried out by the LIGO Scientific Collaboration, a group of 580 scientists at universities worldwide.

Last winter, gamma-ray satellites measured a short but intense outburst of gamma rays originating in the direction of the Andromeda galaxy, located 2.5 million light years away. Such a violent event occurring in a nearby galaxy should have generated gravitational waves that would be easily measured by the ultra-sensitive LIGO detectors, but no waves were recorded.

The eighteen member strong UWM LIGO group has been a significant contributor to the LIGO effort since 1996. "This was an exciting opportunity for us to contribute directly to the study of GRBs," said Brady. The LIGO analysis provided information that could not be obtained by observations with other telescopes, he added.

"This result is not only a breakthrough in connecting observations in the electromagnetic spectrum to gravitational wave searches, but also in the constructive integration of teams of complementary expertise," says Szabolcs Marka, an assistant professor of physics at Columbia University in New York.

The next major construction milestone for LIGO will be the beginning of the Advanced LIGO Project, which is expected to start in 2008. Advanced LIGO, which will use the infrastructure of LIGO, will be 10 times more sensitive. The increased sensitivity will be important because it will allow scientists to detect cataclysmic events such as black-hole and neutron-star collisions at 10-times-greater distances.

Further reading:

• Implications for the Origin of GRB 070201 from LIGO Observations, B. Abbott et al. [LIGO Scientific Collaboration]