The largest black hole merger ever observed has resulted in a new black hole about 225 times the mass of our Sun. The collision was detected using the LIGO gravitational wave observatories.
LIGO detector in Hanford, Washington. Credit: LIGO.
Gravitational waves were first detected at the US Laser Interferometer Gravitational-Wave Observatory (LIGO) in 2015. These waves, first postulated by Einstein in his general theory of relativity, are ripples in the fabric of spacetime caused by the most violent events in the cosmos.
Since then, gravitational wave observatories have detected hundreds of black hole mergers. The LVK network of detectors alone has spotted about 300 in the last 10 years. LVK is a collaboration involving LIGO, the Virgo detector in Italy and KAGRA (Kamioka Gravitational Wave Detector) in Japan.
The new merger, GW231123, was detected on 23 November 2023. Astronomers pouring over the data have determined that the event saw the collision of 2 black holes, each 100–140 times the size of the Sun.
Infographic on the binary binary black hole merger that produced the GW231123 signal. Credit: Simona J. Miller/Caltech.
Previously, the biggest black hole merger, GW190521, involved black holes with a combined mass 140 times that of the Sun.
GW231123’s discovery and its implications for astrophysics is being presented at the 24th International Conference on General Relativity and Gravitation (GR24) and the 16th Edoardo Amaldi Conference on Gravitational Waves, held in Glasgow, Scotland from 14 to 18 July.
“This is the most massive black hole binary we’ve observed through gravitational waves, and it presents a real challenge to our understanding of black hole formation,” says LVK collaboration member Mark Hannam, from Cardiff University in Wales.
“Black holes this massive are forbidden through standard stellar evolution models. One possibility is that the 2 black holes in this binary formed through earlier mergers of smaller black holes.”
Gravitational wave observations have allowed astronomers to observe events like GW231123 which test the limits of known physics.
“The black holes appear to be spinning very rapidly – near the limit allowed by Einstein’s theory of general relativity,” explains LVK member Charlie Hoy from the UK’s University of Portsmouth. “That makes the signal difficult to model and interpret. It’s an excellent case study for pushing forward the development of our theoretical tools.”
“It will take years for the community to fully unravel this intricate signal pattern and all its implications,” adds LVK member Gregorio Carullo from the University of Birmingham, UK. “Despite the most likely explanation remaining a black hole merger, more complex scenarios could be the key to deciphering its unexpected features.”
“This observation once again demonstrates how gravitational waves are uniquely revealing the fundamental and exotic nature of black holes throughout the universe,” says Dave Reitze, the executive director of LIGO at the California Institute of Technology, USA.