Third gravitational wave detected, revealing massive black hole collision

2 Jun 2017

A dancing duo of black holes. Image: LIGO

It seems that the third time’s a charm for LIGO researchers, who have once again detected a gravitational wave.

When the Laser Interferometer Gravitational-Wave Observatory (LIGO) first detected gravitational waves last year, astronomers heralded a new era of understanding for the cosmos.

The ripples in spacetime first theorised by the legendary Albert Einstein were undetected – and therefore unproven in science – until last year’s discovery, despite decades of trying.

Future Human

Thanks to LIGO’s array of incredibly sensitive telescopes, the small ripple was discovered, science rejoiced and the rest is history.

Now, more than a year and a half later, we can celebrate a hat-trick of discoveries with the recording of a new wave. This one, however, is much further out than the two previous discoveries.

In an announcement, LIGO said the “shudder of spacetime itself” arrived at Earth on 4 January, having travelled a distance of 3bn light years away from a far-off galaxy, meaning it occurred not long after the first life forms appeared on Earth.

Based on the findings, the wave was created by an enormous merger between two black holes of varying size – believed to be 19 times and 32 times the mass of our sun, respectively – creating a black hole of 49 solar masses.

As you can probably tell, these figures do not add up to 49, but LIGO explained that the additional two solar masses were forged as pure gravitational wave energy after the merger, which has now arrived here.

Before they merged, the two black holes would have fit into spheres about 115km and 190km in diameter, respectively, but when merged, they would occupy a sphere about 280km across.

To put these numbers into perspective, it would be like putting the same amount of matter as 49 times that of the sun (1.4m km in diameter) into a distance of less than 200km across.

Black holes merging

Illustration of spiralling black holes just prior to their merging. Image: LIGO

Theory of relativity gets a boost

The discovery of a third gravitational wave in the universe adds further credence to Einstein’s 100-year-old theory of general relativity, despite astrophysicists preparing some alternate theories in case it is wrong.

The next step for LIGO is to get its sister detector Virgo in Europe back up and running, and, after that, analyse more sky in the hope of finding ‘afterglow’.

Unlike the darkness found in black holes, afterglow could be leftover stellar matter from a supernova caught up in the merger, and would allow astronomers to understand these events in even greater detail.

“Even though we have yet to detect something that we expect to give off any light,” LIGO said, “the chance of being the first to detect a flash or residual glow associated with a gravitational-wave generating event keeps our astronomical partners interested in any alerts we send them.”

Colm Gorey was a senior journalist with Silicon Republic