black hole merger
Original Published Date: 
Tuesday, April 27, 2021

Full article issued by the ARC Centre of Excellence for Gravitational Wave Discovery.

New ARC-supported research has confirmed that Einstein’s theory of gravity accurately describes current observations of black holes, from the smallest to the largest.

General relativity, Einstein’s theory of gravity, is best tested at its most extreme – close to the event horizon of a black hole. This regime is accessible through observations of the shadows of supermassive black holes which reside at the centre of galaxies, and gravitational waves, which are ripples in the fabric of our Universe from colliding stellar-mass black holes.

The theory provides a specific description of a black hole’s effect on the fabric of space-time: a four-dimensional mesh which describes how objects move through space and time. Known as the Kerr metric, this prediction can be related to the bending of light around a black hole, or the orbital motion of binary black holes. 

For the first time, scientists from the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav), the Event Horizon Telescope (EHT) and the LIGO Scientific Collaboration, have outlined a consistent approach to exploring deviations from Einstein’s general theory of relativity in these two different observations.

In 2019, the EHT generated silhouette images of the black hole at the centre of the galaxy M87, with a mass several billion times that of our Sun. Meanwhile, the LIGO and Virgo gravitational-wave observatories have been detecting gravitational waves from merging stellar mass black holes since 2015. By combining the measurements of the shadow of the supermassive black hole in M87 and gravitational waves from a couple of binary black hole detections, called GW170608 and GW190924, the researchers were able to test Einstein's theory – and they found no evidence for deviations from what it predicted.

'Different sizes of black holes may help break the complementary behaviour seen here between EHT and LIGO/Virgo observations,' says Ethan Payne, co-author of the study and research assistant at OzGrav. 'This study lays the groundwork for future measurements of deviations from the Kerr metric.'

Photo credit: 

Artist's impression of binary black holes about to collide. Credit: Mark Myers, OzGrav-Swinburne University.