It’s not the first merger, but this one in particular deserves it. Even two Italians among those who understood the importance of the event
90 mergers between black holes have been detected since the cutting edge of astrophysics allows these types of recordings. But one of these stands out above all, the one detected in May 2019, called GW19052, which emitted space-time ripples like never before.
“Its morphology and explosion-like structure are very different from previous observations,” explains astrophysicist Rossella Gamba of the University of Jena in Germany. She adds: “GW190521 was initially analyzed as the merger of two rapidly spinning heavy black holes approaching each other in nearly circular orbits, but its particular characteristics led us to propose other possible interpretations.” In particular, astrophysicists have found it difficult to explain the short and sharp duration of the gravitational wave signal emitted by the collision.
Gravitational waves are generated by the actual merging of two black holes, like the ripples of a stone dropped into a pond. In astrophysics jargon, space-time ripples are generated, and the gravitational interaction produces weaker ripples as two black holes inexorably approach each other, attracted to each other.
“The shape and brevity – less than a tenth of a second – of the signal associated with the event lead us to hypothesize an instantaneous merger between two black holes, which occurred in the absence of a spiral phase”, explains astronomer Alessandro Nagar of the Italian National Institute of Nuclear Physics.
The researchers think that the two black holes have become “entangled” in each other; therefore, they designed simulations to test their hypothesis. They brought pairs of black holes together, tweaking parameters such as trajectory, spin and mass, to try to reproduce the strange gravitational-wave signal detected in 2019. The results suggest that the two black holes did not start out as binaries, but are trapped in each other’s gravitational web, rolling close together, then colliding and merging into a single black hole .
This encounter/clash takes the name of a dynamic encounter, and they are considered quite rare. The new study by astrophysicists suggests that GW190521 may be the first that has been detected with certainty.
- GW190521 as a dynamical capture of two nonspinning black holes. (nature.com)