The extremely elusive 'middleweight' black hole


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May 6, 2010
Boston, MA
From 7 billion light-years away, a pair of colliding black holes has delivered up, on a shiny gravitational wave platter, one of the most sought-after detections in black hole astronomy - the extremely elusive 'middleweight' black hole, which lies in between stellar-mass black holes and supermassive behemoths.

Not only, however, did the two colliding black holes combine to form this intermediate-mass black hole, but one of them was another black hole unicorn - falling squarely in what's called the 'upper mass gap', in between stellar-mass black holes and intermediates, where no black holes have ever been detected in the Milky Way.
But hard work analysing it revealed that the product of the merger was a black hole around 142 times the mass of the Sun, and that the two objects that created it were 66 and 85 solar masses. That's more massive than any black hole collision we've detected in the five years since we first detected gravitational waves.
"Right from the beginning this signal, which is only a tenth of a second long, challenged us in identifying its origin," said theoretical physicist Alessandra Buonanno of the Max Planck Institute for Gravitational Physics in Germany and the University of Maryland.

"But, despite its very short duration, we were able to match the signal to one expected of black-hole mergers, as predicted by Einstein's theory of general relativity, and we realised we had witnessed, for the first time, the birth of an intermediate-mass black hole from a black-hole parent that most probably was born from an earlier binary merger."

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