Artist’s impression of binary black holes about to collide. Image: Mark Myers/ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav)
A ‘bang’ of cosmic proportions was detected from the most massive black hole merger to create huge gravitational waves.
Ripples from an extreme astrophysical phenomenon, known as gravitational waves, have been observed at a scale greater than anything seen before. Writing in The Astrophysical Journal Letters, researchers from the Laser Interferometer Gravitational-wave Observatory (LIGO) and Virgo detectors detailed the discovery of a gravitational wave from what may be the most massive black hole merger yet.
The product of the merger is the first clear detection of an ‘intermediate-mass’ black hole, with a mass between 100 and 1,000 times that of the sun. The signal, labelled GW190521, was detected on 21 May 2019 and resembled four short wiggles that lasted less than a fraction of a second.
Estimates suggest the cataclysmic event occurred approximately five gigaparsecs away when the universe was half the age it is now. This makes it one of the most distant gravitational-wave sources detected so far.
Almost every confirmed gravitational wave signal was generated by a binary merge, either between two black holes or two neutron stars. In this case, the most likely merger was between two black holes with masses of about 85 and 66 times that of the sun.
Not a chirp
The resulting merger released an incredible amount of energy equivalent to eight solar masses to create a single black hole with about 142 solar masses.
“This doesn’t look much like a chirp, which is what we typically detect,” said Virgo member Nelson Christensen, a researcher at the French National Centre for Scientific Research.
“This is more like something that goes ‘bang’, and it’s the most massive signal LIGO and Virgo have seen.”
Another interesting finding made by the researchers was that the spin of each of the black holes could have been within their own axes at angles that were out of alignment with the axis of their orbit. These misaligned spins likely caused their orbits to wobble as they spiralled towards one another.
Pedro Marronetti, programme director for gravitational physics at the US National Science Foundation, said: “LIGO once again surprises us not just with the detection of black holes in sizes that are difficult to explain, but doing it using techniques that were not designed specifically for stellar mergers.”
