An multinational effort lead by Penn State academics has produced the world’s largest catalog of gravitational wave incidents. Gravitational waves are ripples in space time that occur as a result of massive astronomical events like the colliding of two black holes. The research team found 35 gravitational wave occurrences using a global network of detectors, bringing the total number of observed events to 90 since detection efforts began in 2015.
Between November 2019 and March 2020, three worldwide detectors observed new gravitational wave events: the two Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors in Louisiana and Washington state in the United States, and the Advanced Virgo detector in Italy. A team of scientists from the LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration meticulously analyzed data from these three detectors. A report published on the preprint service arXiv on Nov. 7 details the catalog of new events discovered during the second half of LIGO’s third observing session.
“We have begun to find the more elusive forms of gravitational wave events in the third observation run of LIGO and Virgo,” said Debnandini Mukherjee, a postdoctoral researcher at Penn State and a member of the LIGO collaboration. “Heavy mass black holes, more extreme mass ratio binaries, and neutron star–black hole coalescences with higher confidence have all been discovered.” We are living in an exciting period in which such findings have begun to cast doubt on previously held beliefs in astrophysics and have begun to contribute to a better understanding of how such objects form.”
There have been some new discoveries
32 of the 35 events detected were most likely black hole mergers, which involve two black holes swirling around each other and eventually merging, resulting in a burst of gravitational waves.
The black holes engaged in these mergers come in a variety of sizes, with the largest being roughly 90 times the mass of our sun. Several of the ensuing black holes, which are classified as intermediate-mass black holes, have a mass greater than 100 times that of our sun. This is the first observation of this form of black hole, which astrophysicists have long predicted.
Two of the 35 events were most likely mergers of neutron stars and black holes, a considerably rarer sort of event first identified during LIGO and Virgo’s most recent observing cycle. A large black hole around 33 times the mass of our sun appears to collide with a very low-mass neutron star about 1.17 times the mass of our sun in one of the recently discovered mergers. Using gravitational waves or electromagnetic studies, this is one of the smallest neutron stars ever discovered.
Black hole and neutron star masses are important indicators of how enormous stars live and die in supernova explosions.
“We were finally able to witness mergers of black holes with neutron stars in this recent update to the catalog, something we hadn’t found in any of the previous observation runs,” said Becca Ewing, a graduate student at Penn State and a member of Penn State’s LIGO group. “We discover signals with new and distinct qualities with each successive observation run, expanding our understanding of how these systems might look and function.” As a result, with each new observation, we can begin to increase our understanding of the cosmos.”
A merger of a black hole with a mass of roughly 24 times that of our sun with either a very light black hole or a very heavy neutron star with a mass of around 2.8 times that of our sun produced the final gravitational wave event. The study team has concluded that it is most likely a black hole, but they cannot be certain. In August 2019, LIGO and Virgo observed a similar ambiguous event. Scientists believe that the maximum massive neutron star that can be before collapsing to produce a black hole is roughly 2.5 times the mass of our sun, thus the mass of the lighter object is intriguing. However, no black holes with masses less than 5 solar masses had been identified using electromagnetic measurements. This led scientists to theorize that stars in this range do not collapse to form black holes. These ideas may need to be changed in light of the latest gravitational wave observations.
From the gravitational waves released by these events, the LIGO-Virgo collaboration has identified a wide range of cosmic collisions, including collisions between two black holes and black holes and neutron stars. Each line in this diagram represents a compact binary merger, which contains the two merging objects as well as the remaining merger remnant. Blue represents black holes, orange represents neutron stars, and gray represents compact objects of unknown nature.Credit: LIGO-Virgo Collaboration/Frank Elavsky, Aaron Geller/Northwestern. All Rights Reserved.
Since the initial detection of gravitational waves in 2015, the number of detections has exploded. Gravitational wave scientists have gone from discovering these vibrations in the fabric of the cosmos for the first time to observing numerous occurrences every month, and even many events on the same day, in a matter of years. The gravitational wave detectors achieved their best-ever performance during this third observing cycle, thanks to a program of continuous modifications and maintenance to increase the performance of the pioneering sensors.
Scientists have updated their analytical tools to assure high accuracy of data as the pace of gravitational wave detections grows. Astrophysicists will be able to examine the physics of black holes and neutron stars with unprecedented precision because to the growing library of observations.
Another noteworthy development in this current run was that astronomers made a call to other observatories and detectors around the world within minutes of the initial gravitational wave detections. To try to locate the source event, this network of neutrino detectors and electromagnetic observatories concentrated on the area of sky where the waves were originating from. Gravitational waves can also emit neutrinos and electromagnetic emissions, which, if detected, can provide additional information about the cosmic event. There is no known analogue to any of the recently announced gravitational waves.
Bryce Cousins, an assistant researcher at Penn State and a member of the LIGO team, said, “Rapidly connecting with other observatories is vital to discover counterparts and contribute to multi-messenger astronomy.” “By examining a cosmic event using various signals, we can learn not just about the features of black holes and neutron stars, but also about broader fields of astrophysics like stellar evolution and the expansion of the universe.” In future observing runs, the alert systems and observatory networks developed during this observing run will be critical for finding the counterparts we need to better comprehend these themes.”
The KAGRA observatory in Japan will join the search for the next full observing period, which is slated to begin next summer. KAGRA, which is tucked away deep behind a mountain, completed its first successful observational run in 2020, but it has yet to join LIGO and Virgo in making cooperative observations. Potential events can be located more precisely with more detectors.
“KAGRA joining the detector network can help improve the sky localization area of gravitational wave candidate sources by about a factor of two,” said Shio Sakon, a graduate student at Penn State and a member of the LIGO collaboration. “KAGRA joining the detector network can help improve the sky localization area of gravitational wave candidate sources by about a factor of two, which can then benefit detections of counterparts because knowing the precise locations of the sources in the sky is crucial for telescopes to make observations “With the advancement of the detection pipeline, upgrades to LIGO and VIRGO, and KAGRA’s participation in the detector network, we expect to detect and analyze gravitational waves candidate events more frequently than ever before, and sending out high-quality low-latency public alerts will be crucial to the advancement of multi-messenger astronomy,” says the team.
The gravitational-wave observatories are as follows:
This content is based on research financed by the National Science Foundation’s LIGO Laboratory, a major NSF institution. Caltech and MIT, which developed LIGO and spearheaded the Advanced LIGO detector project, run it. The NSF provided the bulk of the funding for the Advanced LIGO project, with the Max Planck Society in Germany, the Science and Technology Facilities Council in the United Kingdom, and the Australian Research Council-OzGrav in Australia also making major promises and contributions. The LIGO Scientific Collaboration, which includes the GEO Collaboration, brings together around 1,400 scientists from around the world to evaluate data and develop detector designs. The LIGO website has a list of more LIGO collaborators.
The Virgo Collaboration now has around 650 members from 119 institutions in 14 countries, including Belgium, France, Germany, Hungary, Italy, the Netherlands, Poland, and Spain. The Virgo detector is housed in the European Gravitational Observatory near Pisa, Italy, and is funded by the French Centre National de la Recherche Scientifique, the Italian Istituto Nazionale di Fisica Nucleare, and the Dutch Nikhef. The Virgo website has a list of Virgo Collaboration groups as well as further information.
Kamioka, Gifu, Japan, is home to the KAGRA detector. The project is co-hosted by the National Astronomical Observatory of Japan and the High Energy Accelerator Research Organization. The host institute is the University of Tokyo’s Institute of Cosmic Ray Researches. KAGRA was completed in 2019 and thereafter joined the LIGO and Virgo international gravitational-wave networks. The actual data collection began in February 2020, during the “O3b” stage of the race. Over 470 people from 11 countries and areas make up the KAGRA partnership. The KAGRA website has a list of KAGRA researchers as well as extra information.