LIGO keeps on catching waves. The gravitational wave observatory has announced four more detections of the ripples in spacetime, all from pairs of black holes spiraling towards one another and colliding.
According to earlier anouncements by the LIGO team over the last three years, they have already detected gravitational waves from the collisions ofĀ one pair of neutron stars, four pairs of binary black holes, and one pair of black holes that we werenāt quite sure about. A new paper published at the end of last weekĀ confirmsĀ that four additional events were detected ā and also that the uncertain detection really was a signal. This means that LIGO has now detected gravitational waves from 11 different events: ten from pairs of black holes and one from a pair of neutron stars.
TheĀ four new detections were found in a hunt through data from LIGOās previous observations. Researchers had spotted hints of them in 2017, but they werenāt as āloudā as the detections that had already been reported, so they required a more careful analysis, says LIGO team memberĀ NelsonĀ Christensen at Carleton College in Minnesota.
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One of the four black hole mergers was between a black hole about 34 times the mass of the sun and one about 50 times the mass of the sun, the most massive black hole LIGO has ever seen. It was also the most distant at nearly 9 billion light years away.
The sizeĀ is curious, because a single star is unlikely to be able to collapse to form a black hole that big, says Christensen. āItās sort of at the limit of what you might expect from stellar evolution, so maybe this big black hole was formed by a previous merger of other, smaller black holes,ā he says, āMaybe itās black holes all the way down.ā
This is just a taste of the huge haul of detections expected to come in LIGOās next observing run in 2019. āWe should have another 50 events from the next run, if not more,ā says Christensen.
In October, Ā鶹“«Ć½ reported concerns that LIGOās observations may not actually prove that they have spotted any gravitational waves, because of confusion over the techniques they use to analyse the noise in their detectors. The new paper may go some way towards ironing out that controversy.
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