Jun 2, 2017

Gravitational waves: Third detection of deep space warping

The signals were picked up by the Advanced LIGO facilities in the US and are determined to have come from the merger of two huge black holes some three billion light-years from Earth.

It is the third time now that the labs' laser instruments have been perturbed by the warping of space-time.

The detection confirms that a new era in the investigation of the cosmos is now truly under way.

"The key thing to take away from this third, highly confident event is that we're really moving from novelty to new observational science - a new astronomy of gravitational waves," said David Shoemaker, spokesperson for the LIGO Scientific Collaboration.

The latest detection, which was made at 10:11 GMT on 4 January, is described in a paper accepted for publication in the journal Physical Review Letters.

Once again, it is a merger of black holes, and once again the energy scales involved are extraordinary.

The analysis suggests the two black holes that coalesced had starting masses that were just over 31 times and 19 times that of our Sun. And when they finally came together, they produced a single object of a little under 49 solar masses.

It means the unison radiated a simply colossal quantity of pure energy.

"These are the most powerful astronomical events witnessed by human beings," explained Michael Landry, from the LIGO lab in Hanford, Washington State.

"In this case two times the mass of the Sun were converted into deformations in the shape of space. This energy is released in a very short space of time, and none of this comes out as light which is why you have to have gravitational wave detectors."

As with the two previous observations - in September and December 2015 - the scientists are uncertain about where on the sky the 4 January event occurred. From the three millisecond gap between the signal being picked up first at Hanford and then at the second lab in Livingston, Louisiana, researchers can only specify a large arc of possibility for the source.

Conventional telescopes were alerted to go look for a coincident flash of light, but they saw nothing that could be confidently ascribed to the black hole merger.

The LIGO collaboration will only solve this triangulation problem when a third station called VIRGO, in Italy's Pisa province, starts work alongside the US pair this summer.


BBC

By Jonathan Amos