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 of聽one pair of neutron stars, four pairs of binary black holes, and one pair of black holes that we weren鈥檛 quite sure about. A new paper published at the end of last week聽confirms聽that four additional events were detected 鈥� 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.
The聽four new detections were found in a hunt through data from LIGO鈥檚 previous observations. Researchers had spotted hints of them in 2017, but they weren鈥檛 as 鈥渓oud鈥� as the detections that had already been reported, so they required a more careful analysis, says LIGO team member聽Nelson聽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 size聽is curious, because a single star is unlikely to be able to collapse to form a black hole that big, says Christensen. 鈥淚t鈥檚 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,鈥� he says, 鈥淢aybe it鈥檚 black holes all the way down.鈥�
This is just a taste of the huge haul of detections expected to come in LIGO鈥檚 next observing run in 2019. 鈥淲e should have another 50 events from the next run, if not more,鈥� says Christensen.
In October, New 杏吧原创 reported concerns that LIGO鈥檚 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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