Emanuele Berti bio photo

Emanuele Berti

Professor, Johns Hopkins University

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Our new paper in Physical Review Letters is about GW190412, a very unusual binary black hole merger. This event is unusual because one of the two merging black holes has a very large mass (although not as large as the monsters in GW190521, announced just yesterday). It is also unusual because the more massive black hole is definitely spinning.

There are two main ways in which black hole mergers are thought to form. The first is known as a “field formation”: two neighboring stars, after billions of years, explode to form two neighboring black holes that eventually merge. In this case, the black holes are like a couple being together all their lives. The other path involves dynamical interactions: something like a galactic party, where thousands of black holes occasionally pair up and a third may knock the couple apart. These chance meetings can occur more than once, and they may explain why some of these black holes are so heavy: maybe the parent black holes have already merged once, or even more often. Davide Gerosa and I studied this possibility in a 2017 paper.

So, are black holes monogamous or not? The dynamical scenario involves chance encounters similar to that described in Bob Dylan’s Simple Twist of Fate, from Blood on the Tracks. However, multiple chance encounters can only explain GW190412 as long as the black holes met in a very dense environment, such as a nuclear star cluster. The LIGO/Virgo Collaboration found that this scenario could also explain the formation of the gigantic GW190521 black holes.

You can read more about our paper in the press releases from MIT and the University of Birmingham.

Also: congratulations to Davide Gerosa, who received a well-deserved ERC Starting Grant!