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Hunting for Gravitational Waves
August 1, 2014   
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More than a dozen scientists from Poland are among 700 researchers working on an international project to design more sensitive gravitational wave detectors, in an effort to solve one of the fundamental riddles in modern astrophysics.

Gravitational waves are believed to be ripples in the space-time continuum that carry energy across the universe. They have never been directly detected, though there is strong evidence they exist. Such waves were first postulated in the early 20th century by Albert Einstein under his general theory of relativity.

In several years, detectors being developed as part of the international Virgo and LIGO projects are expected to provide information about space and time that may be impossible to obtain in any other way.

The strongest sources of gravitational waves are binary systems that contain objects such as black holes and neutron stars, which are still little understood by scientists.

“Existing technology makes it possible to finally build extremely sensitive detectors of these waves thanks to which in a few years we will be able to verify the predictions of Einstein’s general theory of relativity and observe the universe. Perhaps we will see objects that we did not realize existed,” says Dorota Rosińska, Ph.D., from the Institute of Astronomy at the University of Zielona Góra in western Poland, who is a member of the international research team taking part in the Virgo and LIGO projects.

Direct detection of gravitational waves is one of the fundamental challenges of modern astrophysics. So far the existence of such waves was only confirmed indirectly in a discovery that ended with the Nobel Prize in Physics in 1993 for Russell Hulse and Joseph Taylor, both from America’s Princeton University, for the discovery of a new type of pulsar. The pair were praised for opening up new possibilities in the study of gravitation.

“In theory, we know that the strongest sources of gravitational waves are merging black holes in binary systems,” says Rosińska. “These holes will most likely be the first objects that will be registered during the second-generation Virgo and LIGO experiments. We also hope to see the very beginnings of the universe, observe supernovae and colliding neutron stars in binary systems.”

Gravitational waves interact only weakly with matter and they travel through space virtually unhindered. The detectors of these waves—Virgo near Pisa in Italy and the LIGO facilities in Hanford in the U.S. state of Washington and in Livingston, Louisiana—are called interferometric observatories. Their job is to measure the amplitude of a gravitational wave. Work is under way to increase the sensitivity of these detectors more than tenfold.

Using funds from the Foundation for Polish Science as part of the Focus program, Rosińska has established a team researching the sources of gravitational waves. She also raised money for another pioneering project involving “numerical tools for the astrophysics of compact objects.” Her team is working to create software for solving problems of relativistic astrophysics and thus explain the nature of so-called compact objects such as black holes and neutron stars.

“We are numerically modeling compact objects and computing the signal—in a sense, fingerprint—of each astrophysical source. With these digital models, specific to each astrophysical object, it will be possible to identify the signal coming from them in the data obtained from the detectors,” says Rosińska.

The Polish team is working with experts from research institutes in France, Germany, Greece and the United States. It currently consists of six doctoral students and several researchers with a Ph.D. degree. Once tested, the software will be made available to other research groups in Poland and abroad.

So far a particularly important achievement has been the creation of a relativistic numerical program in collaboration with the University of Jena in Germany, Rosińska says. The program makes it possible to study hot neutron stars that form inside a supernova or result from the merging of two neutron stars in a binary system. These objects can be important sources of gravitational waves.

The scientists say their numerical program is exceptionally stable and accurate and facilitates thorough modeling of hot neutron stars at different stages of their evolution. The results will be used to study the stability of these objects, which can be strong sources of gravitational waves and X-rays. This is important for understanding the final stages of the evolution of binary systems of neutron stars and supernova explosions.

In a separate endeavor, the team says it has created software for testing what are known relativistic effects in the vicinity of rotating neutron stars and black holes in so-called low-mass X-ray binary systems.

Karolina Olszewska
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