Results confirm new population of black holes
Results confirm new population of black holes
A third detection of gravitational waves, ripples in space and time, has been made. As was the case with the first two detections, the waves were generated when two black holes merged to form a larger black hole. The new-found black hole, located about 3 billion light-years away (twice as far away than the two previously discovered systems), has a mass of about 49 times that of our Sun, an intermediate value between those previously detected in 2015 (62 and 21 solar masses for the first and second detection, respectively).
The discovery is described in a new article accepted for publication in the journal Physical Review Letters. The event occurred on January 4th, 2017, during the current observing run of the twin LIGO detectors in Hanford, Washington, and Livingston, Louisiana, which began 30 November 2016 and will continue through the summer, when the Virgo detector in Europe will join to improve the pointing capability of the entire detector network.
"With this third detection we confirm the existence of an unexpected population of stellar-mass black holes that are larger than 20 solar masses," says Jo van den Brand of Nikhef and VU University Amsterdam, the newly elected spokesperson for the Virgo Collaboration, a body of more than 280 international scientists who perform gravitational waves research together with the LIGO Collaboration. "The entire LIGO and Virgo scientific collaborations worked together to make these amazing detections of such extreme events that took place billions of years ago."
The third detection, called GW170104, was carefully analysed by the LIGO Scientific Collaboration (LSC) and the European-based Virgo collaboration. This is a group of more than 1,200 researchers from more than 100 scientific institutions, spread over four different continents. Previously, this worldwide effort successfully led to the first-ever direct observation of gravitational waves in September 2015 during the first observing run of the LIGO detectors. Then, a second detection was made in December 2015. In all three cases, the detected gravitational waves were generated by extremely energetic collisions of black hole pairs – events that produce more power during the instant before the black holes merge, than is radiated as light by all the stars and galaxies in the observable Universe at any given time.
Dutch scientists closely involved
Just like with the first two detections of gravitational waves, Dutch scientists were closely involved in this third detection. As members of the 'LIGO Scientific Collaboration - Virgo Collaboration' (LVC) physicists from the National Institute for Subatomic Physics (Nikhef) and VU University Amsterdam, as well as astronomers from Radboud University made vital contributions to validating the measurement, to the data analysis for these gravitational waves, and they collaborated on the astrophysical interpretation. More details about the Dutch contribution can be found further on in this press release.
Stan Bentvelsen, director of Nikhef, is excited: "With this third detection we can rightfully say that gravitational waves research is yielding results. This detection is spectacular and we can learn a lot from it. In the coming years it will be a challenge to further increase the sensitivity of the equipment in order to see these processes more often and for us to be able to follow them for longer.
Clues about rotation
As pairs of black holes spiral around each other, they can also rotate around their own axes, the way the Earth and the Moon do, for example. The speed at which they rotate and the angle that their axes possibly make with the orbital plane affect the signal and can thus in principle be determined from the measurement. This is, however, very difficult and so far it was only clear that the black holes were either slowly turning or strongly tilted. The new measurement indicates that at least one black hole is tilted away from the orbital plane. "This is important information about the formation of this binary black hole system", says Samaya Nissanke, astronomer at Radboud University. "If they originate from a double star, the stars, which are unlikely to be tilted, should tip strongly when collapsing into a black hole. If the black holes are formed separately and, through dynamic interactions, a double system has been formed, every angle between the axis of rotation and the orbital plane is possible."
Einstein’s general theory of relativity put to the test again
"We have again put Albert Einstein's theories to the test by looking for an effect called dispersion", says Chris van Den Broeck of Nikhef. This occurs when light waves in a physical medium such as glass travel at different speeds depending on their wavelength; this is how a prism creates a rainbow. "Einstein's general theory of relativity forbids dispersion from happening in gravitational waves as they propagate from their source to Earth. It looks like Einstein was right - even for this new event, which is two times farther away than our first detection. We can see no deviation from the predictions of general relativity."
Advanced Virgo
Virgo has undergone a major upgrade programme called Advanced Virgo. A first engineering run with all systems operational was completed successfully in the first week of May. The sensitivity is improving rapidly and Virgo is expected to soon join the LIGO detectors in our quest to obtain a deeper understanding of the origin and evolution of our Universe.
"There is great excitement among the commissioning team and the scientists from the whole Virgo collaboration", says Alessandro Bertolini of Nikhef. "Some month ago the installations for Advanced Virgo were completed, and now the detector is being commissioned. We can already conclude that the detector is capable of a very robust operation. At the moment, we are focusing a lot of our efforts on reducing background noise.
We are very much looking forward to Virgo soon joining the LIGO detectors for the current observing run. After that run is completed, all three detectors will undergo the foreseen mid-term upgrade to further boost their sensitivity."
About LIGO and Virgo
LIGO is funded by the NSF, and operated by Caltech and MIT, which conceived and built the project. More than 1,000 scientists from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. Additional partners are listed at http://ligo.org/partners.php.
VIRGO research is carried out by the Virgo Collaboration, consisting of more than 280 physicists and engineers belonging to 20 different European research groups: 6 from Centre National de la Recherche Scientifique (CNRS) in France; 8 from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; 2 in The Netherlands with Nikhef; the MTA Wigner RCP in Hungary; the POLGRAW group in Poland; and the European Gravitational Observatory (EGO), the laboratory hosting the Virgo detector near Pisa in Italy. Recently, also Spain joined the Virgo collaboration, with a new group in Valencia.
Dutch contributions
Nikhef makes important contributions to both instrumentation and data analysis within the LIGO-Virgo collaboration. In particular Nikhef is working on the software for the detection and modelling of gravitational waves originating from merging black holes and neutron stars, but also for the search for continuous gravitational waves from, for example, rapidly rotating neutron stars in binary systems.
For the Advanced Virgo detector, which will be commissioned this year as an extension of the LVC network, Nikhef is responsible for seismic isolation and for optical sensors that have to guarantee the stable functioning of the instrument. Nikhef is also playing an important role within the Einstein Telescope project, a future observatory for gravitational waves.
The astronomers from Radboud University are focusing on the astrophysical interpretation and the combination of gravitational wave information with data from traditional telescopes. For this they are developing, amongst other things, the BlackGEM telescope within the Netherlands Research School for Astronomy.
About Nikhef
The National institute for subatomic physics (Nikhef) performs research in the area of particle and astro-particle physics. Nikhef is a partnership between the Netherlands Organisation for Scientific Research (NWO) and five universities: Radboud University, University of Amsterdam, University of Groningen, Utrecht University and VU University Amsterdam.
www.nikhef.nl
Radboud University is also an independent member of Virgo.
More information
Images, videos, animations, and further background information can be found at the Nikhef website
Physical Review Letters: article and supplementary material
For more information, please contact
Vanessa Mexner
Science Communications Department Nikhef
+31 20 592 50 75 / 020 592 2075
Prof. Jo van den Brand
Programme leader gravitational physics group Nikhef and professor of subatomic physics VU University Amsterdam
+31 20 592 20 15 / +31 6 20 53 94 84
Prof. San Bentvelsen
Directeur Nikhef
+31 20 592 50 01 / +31 6 51 11 12 84
Dr. Chris van den Broeck
Senior researcher gravitational physics group Nikhef
+31 20 592 20 53 / +31 6 25 13 39 68
Dr. Alessandro Bertolini
Senior researcher gravitational physics group Nikhef
+31 20 592 20 95
Prof. Gijs Nelemans
Head of astronomy department, Radboud University & KU Leuven and affiliated to Nikhef
+31 24 365 29 83 / +31 6 45 12 01 89
Dr. Samaya Nissanke
Assistant professor astronomy
Radboud Universiteit and leader Radboud Virgo
+31 6 51 97 67 36