A third detection of gravitational waves, ripples in space and time, has been made. The scientist from the Astronomical Observatory of the University of Warsaw contributed to this discovery.


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 during the current observing run of the twin LIGO detectors in Hanford, Washington, and Livingston, Louisiana, which began November 30, 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 – he adds.


A third detection of Gravitational Waves


The third detection, called GW170104 and made on January 4th, 2017, was carefully analysed by the LIGO Scientific Collaboration (LSC) and the European-based Virgo collaboration. This is a group of more than 1200 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.


Black holes like a pair of ice skaters


The newest observation has also generated a lively discussion about the directions in which the black holes are spinning. As pairs of black holes spiral around each other, they also spin on their own axes. This is similar to a pair of ice skaters spinning individually while also circling around each other. Black holes can spin in any direction. Sometimes black holes spin in the same overall orbital direction as the pair is moving – what astronomers refer to as aligned spins – and sometimes they spin in the opposite direction. What’s more, black holes can also be tilted away from the orbital plane. Unfortunately, at the moment the data analysis can not provide definitive information on BH spins. If these colliding black holes are fast rotators, it would mean that at least one of the black holes may have been non-aligned to the overall orbital motion, offering hints about how the pair formed. However, we will have to wait for future LIGO observations to confirm or disprove such notions.


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.


Polish research group POLGRAW being a part of the Virgo Collaboration participated actively in the discovery of GW170104. Prof. Tomasz Bulik from the Warsaw University Observatory is the leader of astronomers from the University of Warsaw involved in this program. The remaining Polish institutions participated in POLGRAW include institutes of the Polish Academy of Sciences, and several Polish universities.