Black hole collisions will revolutionise our perception of the universe
Discovery of the second such event could confirm 100-year-old theory of 'ripple effect' in space from extreme events
Scientists announced that on December 26, 2015 the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected ripples in the fabric of the universe called gravitational waves.
These gravitational waves were generated by two black holes — eight and 14 times the mass of the sun — merging together 1.4 billion light years away from Earth.
This produced a spinning black hole 21 times the mass of the sun. It also released enough energy to rival the mass of the Sun in the form of gravitational waves.
This discovery came just three months after LIGO first detected gravitational waves on September 4, 2015 — one of the most monumental discoveries ever made in physics.
The discovery of gravitational waves confirmed Einstein’s 100-year-old prediction that extremely violent events in space will produce ripples in the fabric of spacetime similar to what would happen if you tossed a pebble into a pond.
Now that scientists have detected two of these events, they’re well on their way to probing some of the darkest, most energetic processes in the universe.
So why are gravitational waves so important?
What we are able to see with light only makes up 0.4 per cent of the universe. The rest of the universe is invisible. We only know it exists because it generates gravity.
Gravitational waves will allow us to listen, in a sense, to that 99.6 per cent of the universe that we can never see.
It's kind as if you're walking in a jungle and you can't hear the sound.
"Without sound you wouldn't detect all the life in the jungle," Stefano Vitale, Principal Investigator for another gravitational wave project, called Laser Interferometer Space Antenna Project (LISA), says. "When you turn on the sound you can recognise the sources - objects you can't see because they're hidden in the jungle. Looking at a gravitational wave is...like adding the soundtrack to the universe. You can see things you cannot see with light."
Studying the universe in gravity could allow us to see as far back in time as the big bang, according to NASA scientist Charles Dunn told. "It's like opening a new window," Oliver Jennrich, ESA deputy project scientist, told says. "All of a sudden we learn about things we had no clue existed."
A whisper in space
But when you toss that pebble into the pond, you might notice that as the ripples spread out on the surface, they get fainter as they get further from where the pebble smacked into the water.
The same thing happens with gravitational waves — by the time they reach us here on Earth they are so faint that they are nearly impossible to detect.
The LIGO detectors each consist of two 2.5 mile arms equipped with a highly sophisticated system of lasers. As a gravitational wave washes over the detectors, the geometry of the arms changes ever so slightly — the shift in arm length can be 10,000 times smaller than a proton.
To measure this incredibly small change, scientists had to make LIGO “more sensitive than any scientific instrument ever built.”
And this new wave that scientists detected was even harder to pick up than the first wave because the black holes were much less massive. This demonstrates just how sensitive the LIGO detectors can be to these waves.
“Because of their lighter masses compared to the first detection, they spent more time— about one second—in the sensitive band of the detectors,” said Gabriela Gonzalez, spokesperson of the international LIGO Scientific Collaboration (LSC). “It is a promising start to mapping the populations of black holes in our universe.”
Because LIGO was able to detect two of these gravitational wave events within its first few months of running, scientists are confident that these sorts of black hole collisions are actually pretty common in our neighborhood.
Being able to study things like black hole mergers through gravity will shed light on some of the "darkest yet most energetic events in our universe,” said Albert Lazzarini, deputy director of the LIGO Laboratory.
“Now that we are able to detect gravitational waves, they are going to be a phenomenal source of new information about our galaxy and an entirely new channel for discoveries about the universe,” said Chad Hanna, co-chair of the Compact Binary Coalescence Group at LIGO.
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