When it rains, it pours. After waiting for 100 years since the first prediction of the existence of gravitational waves, scientists have detected them three times in the last two years.
The details of the latest detection, made on Jan. 4 this year, were published today (June 1) in the journal Physical Review Letters. These particular gravitational waves come courtesy of two black holes merging to become one that is about 50 times the mass of our sun.
“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,” MIT’s David Shoemaker said in a statement.
More importantly, it implies that astronomers have now firmly opened a new window through which they can study the world. Now that astronomers have detected three separate sets of gravitational waves in such a short period of time, it’s almost certain they’ll keep seeing more of them.
Albert Einstein was the first to propose gravitational waves would exist in his theory of general relativity. As he predicted (and scientists have since proven) gravitational waves are ripples in space-time created when massive objects either merge or blow apart. All three wave detections so far have been the result of two black holes merging to become one. These cosmic events are rare, but produce a lot of energy, including gravitational waves. Other events that could create detectable gravitational waves are supernovae (exploding stars) and neutron-star mergers.
In a sense, such an event is like what happens when a stone is thrown in a still pool: the stone disrupts the water, creating waves of water carrying energy away from the spot where it hit; the most violent processes in the universe can disrupt space-time in the same way, radiating waves of distorted space-time.
Though gravitational waves carry tremendous energy, it’s spread out over a very large area, which means that in order to detect them on Earth, we need to use some of the most sensitive instruments scientists have ever built.
The three detections made so far come from two labs that form part of the Laser Interferometer Gravitational-Wave Observatory (LIGO). One is in Hanford,Washington and another in Livingston, Louisiana. As Quartz reported previously, here’s how the detection works:
Each detector consisted of two 4-km long tunnels at right angles. Each tunnel is emptied of all air. A laser beam is split in two, and each beam was sent down one tunnel and reflected back, where they were recombined. Gravitational waves stretch and then contract spacetime as they pass, just as ripples on a pond move the surface up and then down. As they passed through the LIGO team’s lasers, they changed, ever so slightly, the times it took each laser to travel those four kilometers. The distortion would only be as wide as a fraction of the width of a single atom. But that was enough to change the pattern of the laser light where the two beams were recombined.
For most of history, astronomers peered into the sky with telescopes looking at signs of visible light. Over the last century, however, technological advances have allowed them to capture new types of signals which previously weren’t detectable, from radio waves to infrared radiation.
With more confirmed gravitational waves detections, scientists now have another new tool to detect celestial events. And crucially, the events that can be understood with gravitational waves—such as black hole mergers—are those that cannot be seen through common means of detection, such as light.