Rutgers scientists explain significance of gravitational waves
On Thursday morning, researchers at the Laser Interferometer Gravitational-Wave Observatory (LIGO) announced that they had detected gravitational waves. These gravitational waves emanated from two merging black holes that were 1 billion light years away.
The discovery had large ramifications on the field, echoing the sentiments of physicists around the scientific community, said Alyson Brooks, a professor in the Department of Physics and Astronomy.
“This is the biggest announcement since the Higgs Boson,” she said. “Someone got a Nobel for the Higgs, and someone is probably going to get a Nobel for this.”
Gravitational waves were predicted 100 years ago in Albert Einstein’s Theory of General Relativity.
Gravitational waves are oscillations or vibrations, in the field of spacetime, causing a periodic change in the lengths between points and the rate at which time ticks, said Matthew Buckley, a professor in the Department of Physics and Astronomy.
These waves are generated by moving mass and energy around. Energy is what causes spacetime to bend, he said in an email. Simply swinging your hand around can generate a gravitational wave, though not one large enough to detect.
These gravitational waves are similar to waves in electric fields, Brooks said.
“When you have an electron, and move it, the field has to react to the electron,” she said. “So if you oscillate the electron, you set up radiation. A similar thing is happening with the discovery made by LIGO.”
Rather than a moving electron, she said, the LIGO team saw two black holes revolving around each other at about half the speed of light. Their constant change in position continuously altered the spacetime around them and, much like a moving electron, sets up waves in spacetime.
The two black holes that merged were 29 and 36 times the mass of the Sun, respectively. When they merged, three solar masses radiated away, she said. Mass and energy are equivalent through Einstein's equation E = mc2, so this mass turned into the energy for the gravitational wave.
In order to detect gravitational waves, Buckley said that LIGO has to have the ability to measure the length of an object extremely accurately. In this case, LIGO measured the length of “arms," where a laser is at one end and a mirror at the other.
“They use an interferometer, where a laser beam is split and sent down the two arms, each four kilometers long,” he said. “They bounce off the mirror and return to the center and recombine. If the length hasn’t changed ... the beams to interfere destructively and cancel out.”
If a gravitational wave passes through, each arm’s length will change slightly, and the two beams of light will not cancel out perfectly, he said.
The two interferometers operated by LIGO are capable of measuring to an incredible accuracy, Brooks said. The measurements made by LIGO were 1/1000th the size of a proton. Such small changes make the waves hard to find.
Besides confirming Einstein’s Theory of General Relativity, she said this detection was important because it allows astronomers and physicists to observe parts of the universe they haven’t been able to before.
“You shouldn’t see two black holes merge through a telescope, as there’s no light that comes out when they merge,” she said. “There’s no other way with current observational techniques to study this class of object. LIGO opens up a whole new way of observing this aspect of the universe.”
As LIGO discovers more sources of gravitational waves, the scientific community will be able to learn a lot more about the astrophysics behind black hole formation, neutron star formation, supernovae and other astronomical structures, Buckley said.
With the detection coming so quickly after the installation of more advanced detectors at LIGO, Buckley said there might be evidence that black hole collisions happen more often than previously thought.
LIGO is also expanding operations and constructing new interferometers in Italy, India and Japan, Brooks said. This is so when they get future detections, they will be able to better pinpoint where the signal comes from.
As with most scientific discoveries, the biggest results of this detection have not even been thought of yet, Buckley said.
“Gravitational radiation is a new way to see the universe,” he said. “Every time we have opened a new window on the cosmos, we discover something new. I’m sure gravitational waves will surprise us as well.”
Michael Makmur is a School of Arts and Sciences sophomore majoring in astrophysics. He is a staff writer for The Daily Targum. Follow him on Twitter @MikeMakmur for more.