Scientists have detected the most massive source of gravitational waves which has ever been recorded, and aren’t completely sure what caused it.
Every previously observed gravitational wave signal has been detected from some kind of merger between two massive objects, whether black holes or neutron stars.
“Although this event is consistent with being from an exceptionally massive binary black hole merger, and alternative explanations are disfavoured, it is pushing the boundaries of our confidence,” said Professor Alan Weinstein, who was part of the discovery team.
An intermediate-mass black hole is circled. Pic: NASA/ESA/Lin
A gravitational wave is a ripple in space-time caused by a violent event. Gravitational waves were first proposed in 1905 but were not directly observed until 2016.
The following year, in 2017, the Nobel Prize in Physics was awarded to the astronomers who contributed to this achievement, but gravitational waves remain at the edge of humanity’s understanding of the universe
The researchers believe the signal is probably the product of an enormous merger between two black holes, and provides the first clear detection of a so-called “intermediate-mass” black holes potentially 1,000 times more massive that the sun.
Earlier this year other researchers believed they caught an indirect observation of such a so-called missing link black hole when one apparently devoured a nearby star.
But according to Prof Weinstein, at Caltech, the event “opens more questions than it provides answers [for]. From the perspective of discovery and physics it’s a very exciting thing.”
It was recorded on 21 May 2019 and researchers have been analysing it ever since using powerful computers and sophisticated modelling systems.
Gravitational waves are usually caused by mergers of black holes
Named GW1900521, the signal was detected by the US National Science Foundation’s LIGO instrument and a 3km detector in Italy called Virgo.
The signal itself resembles four short wiggles and lasted less than a tenth of a second. It originated from a source roughly five gigaparsecs away – when the universe was about half the age it is now.
The instant the black holes merged they would have released an enormous amount of energy, equivalent to around eight solar masses, which was blasted across the universe in the form of gravitational waves.
The LIGO and Virgo detectors listen for gravitational waves passing through Earth, collecting complicated data which is automatically scanned for signals of these waves.
According to Prof Weinstein, the signal could potentially be from a “cosmic string” from the very earliest moments of the universe, which “potentially makes it extremely exciting”.