Oddball black holes and a tiny neutron star are among the 35 occurrences in the current reward.

The newest collection of cosmic collisions has been provided by gravitational-wave observatories, raising the total number of detections to 90. One of the 35 new occurrences included the lightest neutron star yet observed, as well as two collisions involving unexpectedly big black holes.

The detections came from the two Laser Interferometer Gravitational-Wave Observatory (LIGO) facilities in Louisiana and Washington State, as well as Virgo, their Italian sister detector. They were collected over the course of 21 weeks, commencing on November 1, 2019, with an average detection rate of one incident per 4.2 days. Since then, the partnership has grown to include Japan’s KAGRA detector, which began collecting data in February 2020. In a document published on the arXiv preprint archive, the LIGO–Virgo–KAGRA team summarizes their findings1.

When huge masses accelerate, gravitational waves cause ripples in the fabric of space-time. The newest LIGO–Virgo detections are all ascribed to pairs of dense stellar remnants spiraling into each other and merging, much like the previous ones. The great majority, including LIGO’s initial historic discovery in 2015, comprised pairs of black holes, however a few occurrences had neutron stars as one or both of the objects.

The team initially only published data on high-confidence detections, but the most recent catalogue — as well as the preceding one, published in October 2020 — now contains all detections with a better-than-even probability of being real gravitational waves. According to the researchers, 10–15 percent of the most recent candidates in the database are false alarms generated by “instrumental noise variations.”

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Monster concoction

Researchers can compute the characteristics of a variety of aspects for the objects involved, including their masses and distance from Earth, based on the form and frequency of the waves created by mergers. The distance between the 35 most recent occurrences ranged from 245 million to more than 2.2 billion parsecs (800 million to more than 7 billion light years).

There are some true monsters among them: two of the occurrences featured black holes with masses greater than 60 times that of the Sun. The very presence of these black holes is worrisome for astrophysicists. Black holes are considered to emerge when a large star reaches the end of its life and collapses. However, current models indicate that some dying stars would explode rather than collapse, resulting in a scarcity of black holes in the 65–120 solar mass range.

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