Gravitational waves: astrophysics and source modeling, data analysis, construction of the Virgo detector

LIGO and Virgo make first detection of gravitational waves produced by colliding neutron stars

16.10.17 - Discovery marks first cosmic event observed in both gravitational waves and light.

For the first time, scientists have directly detected gravitational waves — ripples in space and time — in addition to light from the spectacular collision of two neutron stars. This marks the first time that a cosmic event has been viewed in both gravitational waves and light.

The discovery was made using the U.S.-based Laser Interferometer Gravitational-Wave Observatory (LIGO); the Europe-based Virgo detector; and some 70 ground- and space-based observatories. Read more


Virgo congratulates Rainer Weiss, Barry C. Barish and Kip S. Thorne for being awarded the Physics Nobel Prize 2017!

03.10.17 - The Virgo collaboration warmly congratulates Rainer Weiss, Barry C. Barish and Kip S. Thorne on the award of the 2017 Nobel prize in physics ''for decisive contributions to the LIGO detector and the observation of gravitational waves''. The first detection of gravitational waves was announced by the LIGO Scientific Collaboration and the Virgo Collaboration on February 11 2016, five months after the observation of the GW150914 signal, generated by the coalescence of two stellar mass black holes located more than a billion light-years away.

I am delighted that this year’s Nobel prize has gone to our gravitational wave research, says Jo van den Brand, from Nikhef and VU University Amsterdam, the spokesperson of the Virgo Collaboration. The detection of these minute wrinkles in spacetime constitutes an extraordinary achievement. It is the start of a new chapter in our study of the Universe.

Since the first discovery, three more gravitational waves generated two colliding black holes have been detected. The most recent of these detections, on August 14, 2017, was the first one with three detectors at the same time, namely the two Advanced LIGO detectors and the upgraded Advanced Virgo instrument, which jointly operated for 4 weeks starting August 1, 2017.

This first measurements of gravitational waves confirm an important prediction of Albert Einstein's general relativity from 1915. This is the culmination of decades of work, both on the theoretical and experimental sides. Having a three-detector global network opens new prospects for multi-messenger astronomy, adds Federico Ferrini, director of the European Gravitational Observatory (EGO) where the Virgo detector is located.

The LIGO-Virgo global network of three interferometers opens a new era for gravitational wave science by jointly observing a black-hole merger

27.09.17 - The Virgo collaboration and the LIGO Scientific Collaboration report the three-detector observation of gravitational waves. This result highlights the scientific potential of a global network of gravitational wave detectors, by delivering a better localization of the source and historically first time when the polarizations of gravitational waves have been assessed.The three-detector observation was made on August 14, 2017 at 10:30:43 UTC. The detected gravitational waves were emitted during the final moments of the merger of two black holes with masses about 31 and 25 times the mass of the Sun and located about 1.8 billion light-years away. The newly produced spinning black hole has about 53 times the mass of our Sun. This means that about 3 solar masses were converted into gravitational-wave energy during the coalescence.

The Virgo detector joined the Network Observing Run 2 (O2) on August 1, 2017 at 10:00 UTC, after the multi-year Advanced Virgo upgrade program, and months of intense commissioning to improve its sensitivity. The real-time detection was triggered with data from all three LIGO and Virgo instruments.  Even though Virgo is at present less sensitive than LIGO, two independent search algorithms based on all the information available from the three detectors demonstrated the evidence of a significant signal in the Virgo data as well.

Overall, the Universe volume which is likely to contain the source shrinks by more than a factor 20 when moving from a two-detector network to a three-detector network. The sky region for GW170814 has a size of only 60 square degrees, more than 10 times better than for the two LIGO interferometers alone; in addition, the accuracy with which the source distance is measured benefits from the addition of Virgo. Being able to point to a smaller volume is important as many compact object mergers – for example when neutron stars are involved – are expected to produce broadband electromagnetic emission in addition to gravitational waves. The precision pointing information enabled 25 facilities to perform follow-up observations based on the LIGO-Virgo detection but no counterpart was identified – as expected for black holes.

Virgo doesn’t respond in the exactly same way to passing gravitational waves as the LIGO detectors because of its orientation on Earth, meaning that one can test another prediction of general relativity, which is concerned with polarizations of gravitational waves. Polarization describes how space-time is distorted in the three different spatial directions as a gravitational wave propagates. Initial tests based on the transient GW170814 event compare extreme cases: on the one hand, pure general relativity-allowed polarizations; on the other hand, pure polarizations forbidden by Einstein’s theory. The analysis of the data shows that Einstein’s prediction is strongly favored.



A very exciting LIGO-Virgo Observing run draws to a close on the 25th of August

25.08.17 - A very exciting LIGO-Virgo Observing run draws to a close on the 25th of August. The Virgo and LIGO Scientific Collaborations have been observing since November 30, 2016 in the second Advanced Detector Observing Run 'O2', searching for gravitational-wave signals, first with the two LIGO detectors, then with both LIGO and Virgo instruments operating together since August 1, 2017. Some promising gravitational-wave candidates have been identified in data from both LIGO and Virgo during our preliminary analysis, and we have shared what we currently know with astronomical observing partners. We are working hard to assure that the candidates are valid gravitational-wave events, and it will require time to establish the level of confidence needed to bring any results to the scientific community and the greater public (see also this link for updates)

VIRGO joins LIGO for the “Observation Run 2” (O2) data-taking period

01.08.17 - Today, Tuesday August 1st 2017 at 11 CEST, the VIRGO detector based in Europe has officially joined “Observation Run 2” (O2) and is now taking data alongside the American-based twin LIGO detectors. This major step forward for the VIRGO Collaboration is the outcome of a multi-year upgrade program, whose primary goal was to significantly improve the detector performance in terms of sensitivity. More informations.

GW170104: Third direct detection of gravitational waves

01.06.17 - The Advanced LIGO detectors registered in the 4th of January 2017 a merger of a black hole binary system of masses approx. 30 and 20 Solar masses and a formation of a remnant black hole of 49 solar masses and spin parameter of about 0.64, at a distance of about 880 Mpc (corresponding to a redshift z = 0.18). It is likely that at least one of the black holes was spinning opposite the direction of the binary orbit. This is the first detection to show evidence for such a spin configuration. The detection was also used to test the general theory of relativity and to estimate the graviton mass.




Virgo-Polgraw is a Polish team of researchers analyzing the data collected by the LIGO and Virgo detectors in search for gravitational waves predicted by the general theory of relativity by Albert Einstein.

Gravitational waves astrophysics is a new and promising field of research of the Universe. In contrast to the observations of the electromagnetic waves (radio waves, visible light, X-rays and gamma), which are the main source of our current knowledge, we ''listen'' to the Universe by registering minor disturbances of the space-time curvature using the LIGO and Virgo laser interferometric detectors. Gravitational waves are emitted during the largest cosmic cataclysms: mergers of binary systems of neutron stars or black holes, explosions of supernovae, and by other sources, eg. unstable or deformed rotating neutron stars. The direct detection of gravitational waves allows the study of objects that are dark (do not shine in electromagnetic waves), testing the theory of gravity in the dynamic regime of strong gravitational field, and the direct study of the interior of neutron stars which contain the densest and most extreme matter existing currently in the Universe. These informations cannot be currently obtained using other methods.

In addition to the data analysis and the development of the statistical signal detection theory, we modeling astrophysical sources of gravitational waves, make predictions about the population of these sources, search for the electromagnetic waves emission accompanying the gravitational waves and take part in the construction of the Virgo interferometer.

The leader of the Virgo-Polgraw group is prof. Andrzej Królak from the Mathematical Institute PAS. The project is currently financed by an NCN Harmonia grant ,,Udział Polski w projekcie Advanced Virgo'' UMO-2014/14/M/ST9/00707). Polish participation in the Virgo project is on the Polish Roadmap for Research Infrastructure. The group consists of

  1. Institute of Mathematics, PAS
  2. Nicolaus Copernicus Astronomical Center, PAS
  3. Warsaw University Astronomical Observatory
  4. Institute of Astronomy, University of Zielona Góra
  5. Department of Physics, University of Bialystok
  6. National Centre for Nuclear Research
  7. Centre for Astronomy, Nicolaus Copernicus University in Toruń
    • Kazimierz Borkowski
  8. Institute of Theoretical Physics, University of Wrocław
    • Arkadiusz Błaut
  9. Astronomical Observatory of the Jagiellonian University
    • Andrzej Kułak
    • Michał Ostrowski

Financing sponsors and sources of computing grants.

Member of the Virgo-Polgraw group: Paweł Ciecieląg, Magdalena Sieniawska, Orest Dorosh, Izabela Kowalska-Leszczyńska, Dorota Rosińska, Adam Zadrożny, Michał Bejger, Andrzej Królak, Piotr Jaranowski, Tomasz Bulik.

Countries and institutions participating in the Advanced Virgo project (Nicolas Arnaud/Virgo Outreach team)

Members of the LIGO-Virgo Collaboration Meeting, organized in Kraków, September 2010.