Just over a year ago, on April 12, 2019, the LIGO-Virgo collaboration discovered gravitational waves propagating in spacetime from an epic collision of two black holes at a distance of 2.4 billion light years.
But as astronomers have now figured out, the actual collision of GW 190412 was something we had never seen before. Instead of two approximately equal mass black holes, 20-40 times the mass of the Sun, GW 190412 was obtained from an uneven binary system.
Based on an analysis of these pulsating gravitational waves, astronomers found that one of the black holes tipped the scales to about 29.7 solar masses, while the other was three times lighter at just 8.4 solar masses.
It is also the lowest-mass black hole discovered to date – which is extremely exciting because it means their merger gave a longer signal than any other black hole merger – a huge amount of data to explore.
“None of these masses are surprising in themselves. We know black holes come in that size. What is new is the mass ratio, ”explained astronomer Christopher Berry of Northwestern University and the LIGO Collaboration.
“This observation allows us to test our predictions for gravitational wave signals in a new way and is another piece of the puzzle of understanding how binary black holes are formed.”
Based on the unusual fusion signal, the team was able to take several more measurements as well. They were able to determine that the largest of the black holes was spinning.
In GW 190412, this rotation seemed to be quite fast, which may be a clue as to how such an uneven binary system came to be. You see, there are several astrophysical models for the formation of binary black holes, but most of them lead to more or less equal mass pairs.
The most obvious is a binary star system in which each star collapses into a black hole. However, it is believed that they cannot create binary black holes with large discrepancies in mass, except for GW 190412.
It is possible that the black holes formed separately, and then somehow converged, capturing each other in orbit. But the faster spinning of the larger black hole suggests it may have merged with other black holes earlier, before GW 190412.
You can read the full text on the LIGO website.
Sources: Photo: N. Fischer, H. Pfeiffer, A. Buonanno (Max-Planck-Institut für Gravitationsphysik), Simulating eXtreme Spacetimes project
