LIGO gravitational waves: Ripples in spacetime detected for third time from colliding black holes

Ripples in the fabric of spacetime emanating from two black holes crashing into each other about 3 billion light years away have been observed. The two black holes together will form a larger black hole about 50 times larger than the Sun.

Gravitational waves are distortions in the fabric of spacetime created when massive objects accelerate through it. The greater the object, the more ripples it would send out through spacetime.

Black holes are some of the most massive objects in the universe, and can be billions of times bigger than the Sun. When they collide, the biggest gravitational waves would be expected to be created.

The discovery published in the a paper in the journal Physical Review Letters is the third time echoes of gravitational waves have been directly observed. The first observations of gravitational waves were also from colliding black holes. The third has been named GW170104, and was made on 4 January 2017.

David Shoemaker of MIT, and spokesperson for the Laser Interferometer Gravitational-wave Observatory, the facility where the waves were observed, said in a statement: "We have further confirmation of the existence of stellar-mass black holes that are larger than 20 solar masses – these are objects we didn't know existed before LIGO detected them."

"It is remarkable that humans can put together a story, and test it, for such strange and extreme events that took place billions of years ago and billions of light-years distant from us."

The observations are already revealing clues to the nature of black holes – the latest finding suggests that the two black holes in the binary system are not aligned in the way they're spinning, which hasn't been directly observed before.

"We're starting to gather real statistics on binary black hole systems," said Keita Kawabe of Caltech, an editor of the paper based at the LIGO Hanford Observatory.

"That's interesting because some models of black hole binary formation are somewhat favoured over the others even now and, in the future, we can further narrow this down."

Gravitational waves were one of Albert Einstein's key predictions, put forward in 1916. One aspect of his prediction was that the waves would not disperse through space. Dispersion is what happens when light passes through a prism to create a rainbow.

"It looks like Einstein was right – even for this new event, which is about two times farther away than our first detection," said Laura Cadonati of Georgia Tech and the deputy spokesperson for the LIGO Scientific Collaboration.

"We can see no deviation from the predictions of general relativity, and this greater distance helps us to make that statement with more confidence."

The LIGO instruments are now being upgraded, and will be put back to work again in January 2018. It's hoped that with even more sensitivity, the facility could start observing gravitational waves from objects other than black holes.

"We hope to see other types of astrophysical events soon, such as the violent collision of two neutron stars," concluded David Reitze of Caltech, executive director of the LIGO Laboratory.