“Family” of black holes and fusing neutron stars detected

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An international group of astronomers has been able to analyze what appears to be a true family of black holes and neutron stars using gravitational wave signals detected together. Three articles related to the discovery were published, bringing the most detailed survey on this type of systems ever made and offering new clues on the formation of this type of objects.

For this research, the group, formed by scientists from LIGO Scientific Collaboration (LSC) and Virgo Collaboration, analyzed data from the third “round” of observation of gravitational wave signals, called O3a. These observations are made by LIGO itself, an observatory designed to detect these signals. The results are available on arxiv.org and have already been submitted for peer review and eventual publication in scientific journals.

During O3a observations, 39 new candidates have already been observed for detecting gravitational waves that have passed tests that aim to determine whether the signals are really coming from such cosmic waves. And gravitational waves are essentially a phenomenon caused by the interactions of highly massive objects, such as neutron stars and black holes. When a collision between objects of this size occurs, for example, gravitational waves spread throughout the universe, and can eventually be detected by instruments such as LIGO. And that is exactly what happened: the family of black holes and neutron stars is going through a series of collisions, which generated the 39 signals.

This computer simulation shows several black holes found in the heart of a dense globular cluster of stars (Image: Reproduction / Aaron M. Geller, Northwestern University / CIERA)

These observations may end up being essential to mysteries such as the way binary stars interact, and this could bring scientists a new view of the whole of astronomy. “Gravitational wave astronomy is revolutionary – revealing to us the hidden life of black holes and neutron stars,” said Christopher Berry, LSC member and author of the articles. “In just five years, we are no longer unaware of the existence of binary black holes and have a catalog with more than 40,” he said, showing the importance of this type of detection.

Berry explained that O3a, which is actually only the first half of the third “round” of gravitational wave observation, “has resulted in more discoveries than ever” and provides a “beautiful picture of the rich variety of the universe of binaries”. This data helped Berry’s team to infer the properties of the detected black holes and binary neutron stars and also to provide an astrophysical interpretation of these findings.

To get an idea of ​​the size and importance of this series of 39 detections, keep in mind that the first “round” had three detections of gravitational waves, while the second had eight. On those occasions, the first black hole of intermediate mass, the object GW190521, was found. If with so few detections something so important has been discovered, the new observations together have a lot of potential to result in large studies.

In one of the articles, the researchers brought the mass distribution and spin (rotation rate) of the group of black holes and estimated the fusion rate of binary neutron stars. The results will help scientists understand the cosmic mechanisms that drive the formation of these binary systems and objects. For example, studies have shown that black hole spin can be misaligned, which means that there can be several ways binary black holes can form.

In addition, the researchers used the set of detections to combine all of them and perform a test of Einstein’s general relativity, as fusions of black holes and neutron stars are great for testing the implications of German physicist theories on gravity. The result: general relativity has been proven once again.

Gravitational wave simulation (Image: Reproduction / LIGO / T. Pyle)

These researches can still bring a lot of news to astrophysics. In the words of Fishbach, an LSC researcher: “So far, the third series of observations from LIGO and Virgo has yielded many surprises. After the second observation run, I thought we had seen the entire spectrum of binary black holes, but the landscape of black holes is much richer and more varied than I imagined. I’m excited to see what future observations will show us. “

The LIGO and Virgo detectors completed the third round of observations in March this year, but the data analyzed in these three articles was collected from April 1, 2019 to October 1, 2019. Now, scientists are ready to analyze the data of the second half of detections, called O3b. The expectations for new discoveries could not be more exciting!

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