Gravity waves discovery provides researchers with ‘new sense of hearing’

Recent discovery of gravitational waves through a collision of two immense black holes 1.3 billion years ago has physicists rubbing their hands together in glee, Daniel Bardsley reports

Recent discovery of gravitational waves through a collision of two immense black holes 1.3 billion years ago has physicists rubbing their hands together in glee.

The recent announcement that gravitational waves have, at last, been discovered has caused enormous excitement among physicists.

Scientists have spent decades trying to detect these waves after the release a century ago of Albert Einstein’s theory of general relativity, which predicted their existence.

Among the researchers who are especially pleased is Eugenio Coccia, a professor of physics at the University of Rome Tor Vergata and chairman of the gravitational wave international committee.

Prof Coccia collaborates with Dr Francesco Arneodo, an associate professor of physics at New York University Abu Dhabi, as the two share an interest in dark matter. He recently gave a talk at NYU Abu Dhabi on the announcement.

“If I say I’m happy this is not enough for how I feel,” he says.

Prof Coccia has spent 36 years trying to find gravitational waves.

Until now, energy from space had been detected only in the form of radio waves, X-rays, gamma rays and ultraviolet light, which all belong on the electromagnetic spectrum, which includes visible light.

Now, researchers have “acquired a new sense of hearing”, as Prof Coccia puts it.

“I think it’s a new astronomical window. It’s like you can now finally listen to the universe, understand the vibrations of space-time,” he says.

The gravitational wave that was detected was a perturbation or ripple across space created when two black holes, one of them about 36 times the size of the Sun, the other about 29 times, collided about a billion years ago.

“It was possible to measure it because they were two quite big black holes. The 36 and 29 solar masses is a remarkable binary black hole system,” says Prof Coccia.

As one expert told international media, the gravitational wave represented a “storm in the fabric of space-time” in which “time is speeded up and slowed down and speeded up again”, distorting the shape of space.

It was detected by the laser interferometer gravitational-wave observatory (Ligo), which uses two key centres, one in Hanford in Washington state and the other a long way east of this, in Livingston, Louisiana.

At each of these points, a laser beam is split and sent along 4-kilometre vacuum tubes before being reflected back by a mirror.

The gravitational wave, when passing the centres, alters the distance between the mirrors at the ends of the tubes – a minuscule difference that the laser beams can measure.

To describe the chance in the distance between the mirrors as minuscule is an understatement.

It is less than 1,000th the width of a proton, the positively charged type of particle found in the nuclei of atoms.

This explains why detecting gravitational waves has not been easy, and Einstein himself thought the effects they produced would not be strong enough to be detected.

“To detect that you need very advanced technology − very powerful lasers and mirrors that are practically perfect. You need a lot of electronic controls. It’s not easy to measure such a small effect,” says Prof Coccia.

The gravitational wave was detected on September 14 last year and it was the centre in Louisiana that detected it first − by 7 milliseconds.

This difference in time between the two points indicated the direction from which the wave was coming, namely the southern hemisphere.

And researchers think the merging of the black holes that caused the gravitational wave took place 1.3 billion years ago.

Prof Coccia thinks the first gravitational waves to be detected would be those produced by neutron stars, which are highly dense objects typically measuring several tens of kilometres across and made of neutrons. “This is a sort of gift from the sky, this black hole merging. We thought neutron stars coalescing and merging was more frequent than black holes merging. It was a surprise the black hole signal arrived first,” he says.

Now the challenge is to see even further back in time, even as far back perhaps as the Big Bang, which took place about 14 billion years ago.

For this, ever more sensitive detection systems will be required.

“A signal like the one we detected, we can see a signal even more far back than this one by improving the sensitivity of the device,” says Prof Coccia.

One project that will offer “real insight” is eLisa, described by organisers as “the first gravitational wave observatory in space”.

A joint project of eight European countries, with collaborators in the US and Australia, it will create an arm length that is, in effect, 1 million km long, making it much more sensitive than the measuring equipment that recently detected gravitational waves.

The results of the project will, it is hoped, shed light on how galaxies are created and what their structure is like, and on how stars and the universe have evolved.

In December last year, the Lisa Pathfinder Mission was launched, and in January it reached orbit. It should offer a way of testing how gravitational waves can be detected in space.

So although gravitational waves have finally been identified, there are likely to be exciting developments in the years to come.

“I think the next step now is to confirm this signal, to start to look not only at black holes merging, but neutron stars merging. That will give us insight,” says Prof Coccia.

“We have to build a more sensitive interferometer on Earth and in space.

“Even if this experimental research is 50 years old, now it really starts to develop.”