What scientists are saying about LIGO's third discovery of gravitational waves from colliding black holes

The detection of **gravitational waves for the third time** by the Laser Interferometer Gravitational-wave Observatory (LIGO) was the result of a massive collaborative efforts by over 1,000 scientists associated with research institutions and universities around the world. The discovery of gravitational waves for the first time in 2016 was the biggest science story of the year , if not the century. The signal was observed on 4 January, during a **renewed campaign** to hunt for gravitational waves after the LIGO facility received upgrades. [caption id=“attachment_380190” align=“aligncenter” width=“640”]  Image: IGO/Caltech/MIT/Sonoma State (Aurore Simonnet)[/caption] Tyson Littenberg, principal investigator of the LIGO research group at NASA’s Marshall Space Flight Center says, “Up until the success of LIGO, almost everything we knew about the universe came from light. Gravitational wave observations are now firmly part of the toolbox for understanding some of the most exotic objects and violent events in the universe.” The gravitational waves were from a collision between two black holes almost three billion light years away. One of the two black holes was 39 times the mass of the sun, and the other was 19 times the mass of the sun. They spun around each other and collided to form a single massive black hole with about 49 times the mass of the sun. The signal detected from the event lasted only two tenths of a second, during which the black holes whirled around each other six times. [caption id=“attachment_368660” align=“aligncenter” width=“640”]  Black holes colliding. Image: Nasa.[/caption] Erik Katsavounidis, senior research scientist in MIT, and part of the LIGO team, says “Coming from a field of looking for something rare, I’ve always been hesitant, with one detection only, to declare victory. I can tell you I’ve started sleeping much better after the second detection. Now this third one solidifies LIGO and LIGO’s observations as the ultimate tool to see the mass spectrum of black holes in our universe.” One of the most interesting aspects of the new discovery is related to the way in which black holes spin, when whirling around each other and heading towards a collision. One of the two black holes spun in a different direction around its axis than the direction in which the the two black holes moved around each other. This is similar to the teacups on a funfair ride rotating in a opposite direction than the platform. [caption id=“attachment_380193” align=“aligncenter” width=“640”]  Another artist’s impression of the colliding black holes. Image: SXS.[/caption] Georgia Tech Professor Laura Cadonati and LIGO’s deputy spokesperson explains, “As an example, imagine a pair of tornadoes in a clockwise orbit around each other. Both tornadoes also spin on their own axes. It could be in the same clockwise direction as their orbit or it could be in the other direction. They could also be lying down on their orbital plane or at any angle in between. Black holes could do the same thing.” The Australian National University (ANU) contributed to improving the systems on the LIGO detectors, so that observations of longer duration could be undertaken, which increases the chances of finding gravitational waves. Professor Susan Scott from the ANU Research School of Physics and Engineering says “It’s possible this is a binary system of black holes that formed in the early Universe and contributes significantly to the dark matter in the cosmos. This heavy stellar-mass binary black hole system was at a much greater distance than the first two gravitational wave events, at some three billion light years away. This discovery highlights the need to continue improving the sensitivity of our detectors to see further and further out into the Universe.” [caption id=“attachment_380194” align=“aligncenter” width=“640”]  Image: LIGO/ OzGrav[/caption] Sanjit Mitra from the Pune-based Inter-University Centre for Astronomy and Astrophysics (IUCAA), researchers of which have participated in the LIGO discoveries, said “The new event also provides new opportunities to test Einstein’s theory of general relativity. For example, this allowed us to confirm Einstein’s prediction that gravitational waves should not undergo dispersion — the phenomena of waves travelling at different speeds depending on their wavelength. Indian scientists played a leading role in deriving this result”

West Virginia University (WVU) has 6 professors and 2 students working on the LIGO project. Sean McWilliams, assistant professor of Physics and Astronomy at WVU outlines four significant aspects of the latest discovery. The new discovery provides more insight into the spins of black holes. At 49 solar masses, the new discovery is between the two previous discoveries, which were 62 and 21 solar masses. The third important point to note is that this is the most distant detection of such an event, at three billion light years away, the other two events took place less than 1.5 billion light years away. The final important aspect is that the discovery happened during the current campaign with upgraded capabilities, and there are plans to further upgrade the facility before the next campaign. [caption id=“attachment_380196” align=“aligncenter” width=“640”]  Image: LIGO/Caltech/Sonoma State (Aurore Simonnet)[/caption] Jordan Camp, principal investigator for the Goddard LIGO team says “LIGO is unveiling a population of stellar-mass black holes far more massive than those that have been detected through previous observations. The mystery now is how these larger black holes form, and how they end up close enough to one another that we observe them merging so frequently.” India could play a role in such exciting discoveries in the future. India is all set to get **its own LIGO facility by 2024** , the first to be located outside the United States. The project is called IndiGO, and a site in Hingoli, in Maharashtra has been identified. The Indian LIGO facility is expected to be even more advanced than the two LIGO facilities in the United States, and experiments are already under way to create more precise detectors by **using quantum mechanics to squeeze light** .