Gravitational waves caught again
'The second detection of the gravitational waves from merging black holes is very important. The foundation for the gravitational-wave astronomy is becoming stronger and more reliable,' says Valery Mitrofanov, Professor of the Physics Department of the Moscow State University.
Studies are conducted within the LIGO Scientific Collaboration (LSC) — a team of more than 1,000 scientists from the United States and 14 other countries, including Russia. Among the Russian scientists of the LIGO Collaboration is also the staff of the Physics Department of the Moscow State University: Head of the Moscow group, professor of physics of oscillations, Valery Mitrofanov, professors of the Faculty of Physics, Igor Bilenko, Sergei Vjatchanin, Mikhail Gorodetsky, Farid Khalili, Sergei Strygin, assistant Leonid Prokhorov. The development of the detectors and the data analysis involve more than 90 universities and research institutes. About 250 student participants also contribute significantly. LSC detectors network includes LIGO interferometers and the GEO600 detector.
'It is important that the second signal has been generated by the black holes with the relatively small masses, which better corresponds the astrophysicists' predictions. Now we can be more confident that the first event was not a rare exception,' reports Farid Khalili, Professor of the Faculty of Physics of the Moscow State University.
'Gravitational waves, these flying pieces of space-time curvature, from something exotic became a common source of the new information about the universe and opened the era of gravitational astronomy,' describes the situation Sergey Vjatchanin, Professor of the Physics Department of the Moscow State University.
In contrast to the signal recorded on the first detection of gravitational waves, which was clearly visible with the noise on its background, the second signal was weaker and not clear in the noise. However, the scientists were able to 'filter' it with the help of a special technique.
Physicists have come to the conclusion that the observed gravity waves were generated by the two black holes of 14 and 8 solar masses in the last fraction of a second before they merged to form a single, more massive rotating black hole of 21 Solar masses.
During the merger which occurred about 1.4 billion years ago the amount of the energy equivalent to roughly one solar mass has become a gravitational wave. The recorded signal was produced on the last 27 turns of black holes before they merge. The detector in Livingstone recorded the event 1.1 milliseconds before the detector in Hanford, which allows to give a rough estimate of the location of the source on the celestial sphere.
The first detection of gravitational waves, announced February 11, 2016, was a milestone in the development of physics. It confirmed the prediction of the general relativitytheory that Albert Einstein made in 1915, and marked the beginning of the new field of gravitational-wave astronomy. Detection of the two signals within four months of the first Advanced LIGO observations cycle allows predicting how often the signals of the gravitational waves may be detected in the future. Both discoveries were made possible thanks to the more refined Advanced LIGO detectors, which are more sensitive than the first generation of the LIGO detectors and can significantly increase the amount of the probed the universe. The next cycle of observations is scheduled for autumn this year. It is expected that by that time further improvement of the LIGO detectors' sensitivity will be able to enlarge the volume of the probed Universe 1,5 – 2 times. It is also expected that in the second half of this observation cycle the Virgo detector will become operational.
'The new result marks the conversion of LIGO from an extremely expensive scientific experiment into the instrument for the continuous extraction of the otherwise unavailable information about the structure of the Universe,' says Mikhail Gorodetsky, professor of the Physics Department of the Lomonosov Moscow State University. 'The repeating detection of gravitational waves gives a powerful impetus for the creation of a new generation of gravitational wave detectors for the further study of the Universe all over the world,' concludes Sergei Strygin, Associate Professor of the Physics Department of MSU.
Moscow Ligo Scientific Collaboration group
Russia is represented in the Ligo Scientific Collaboration (LS?) with two research groups: the group of the Physics Department of the Lomonosov Moscow State University and a group of the Institute of Applied Physics of the Russian Academy of Sciences (Nizhny Novgorod).
The Moscow group was founded and until recently was headed by Corresponding Member of the Russian Academy of Sciences Vladimir Borisovich Braginsky — the world-famous scientist, one of the pioneers of the gravitational-wave research in the world. The research group included professor of physics of oscillations: I.A. Bilenko, S.P. Vjatchanin, M.L. Gorodetsky, V.P. Mitrofanov, F.Y. Khalili, senior professor S.E. Strygin and assistant L.G. Prokhorov. The immeasurable contribution to the study is made by students, graduate students and technical staff of the department.
The Moscow University group is involved in the project since 1992. From the outset, the main efforts were directed at improving the sensitivity of gravitational wave detectors, determination of fundamental quantum and thermodynamic sensitivity constraints for the development of new measurement methods. Theoretical and experimental studies of Russian scientists were embodied in creating detectors which allowed to directly observe gravitational waves from the merger of two black holes.
The Moscow University research group is presently involved in the development of the next-generation gravitational wave detectors which will replace the current detectors and will provide a significant increase in sensitivity, enabling to detect gravitational wave signals almost on the daily basis. One of such projects is the LIGO-Voyager, which is supposed to use 150 kg of test masses made of monocrystalline silicon, cooled to the temperature of about 120 K, as well as significantly increase the optical power of the interferometer's arms and use compressed light. An important area of research to increase the sensitivity of gravitational wave detectors is the transition from a traditional interferometer scheme recording the displacement of the test mass mirrors to the new scheme allowing better suppression of the quantum fluctuations of light. For example, to the scheme of quantum tests masses speed measurement, proposed by the Moscow State University. The prototype of such a detector is being created at the University of Glasgow.
LIGO Observatory was conceived, built and operated by the California and Massachusetts Institutes of Technology (Caltech and MIT) and funded by the National Science Foundation (NSF) of the USA. The discovery (the report was accepted for publication in the journal Physical Review Letters) based on the data of these two detectors was made collectively by the LIGO scientific collaboration (it also includes the GEO collaboration and Australian Interferometric Gravitational Astronomy consortium) and the Virgo collaboration.
The VIRGO Collaboration consists of more than 250 physicists and engineers belonging to 19 different European research groups: 6 of the National Center for Scientific Research (CNRS) in France; 8 of the National Institute of Nuclear Physics (INFN) in Italy; 2 of the Netherlands (Nikhef); (Wigner RCP) from Hungary; POLGRAW group from Poland and the European Gravitational Observatory (EGO), which provides the VIRGO detector's work near Pisa in Italy.