CHICAGO (CBS) — A century after physicist Albert Einstein predicted their existence, scientists have discovered proof of gravitational waves – ripples created in the fabric of space-time when two black holes collided more than a billion light years away from Earth.
The 1,000-member U.S.-led Laser Interferometer Graviational-Wave Observatory (LIGO) project unveiled its findings Thursday, five months after a pair of observing stations in Washington and Louisiana recorded evidence of the waves sweeping through our solar system.
Adler Planetarium astronomer Shane Larson, a Northwestern University professor who was part of the team that detected the waves, said it’s too early to understand the impact this discovery might have.
“Gravitational waves are just now being discovered, and so the question about what will they mean to your life every day is not something that we can know. That’s something for the future to know,” he said.
Scientists studying the signals concluded that two black holes some 1.3 billion light years away – one with about 29 times the mass of the sun and the other with around 36 solar masses – collided after spiraling closer and closer together at half the speed of light, producing a single black hole with 62 solar masses.
Three solar masses were converted into gravitational waves that radiated outward in all directions. Some of those waves swept through our solar system last September, stretching Earth an infinitesimal amount in one direction and compressing it in a perpendicular direction as they distorted local space.
That is what the LIGO instruments detected at stations near Hanford, Washington, and Livingston, Louisiana. It was the first direct evidence of merging black holes, and the first unambiguous detection of gravitational waves.
“The reason this is a big deal is because this is the first time, one of the first times, that we have the capability of seeing the universe, of studying the universe using something other than light, using something other than our eyes,” Larson said.
Larson said Einstein never thought it would be possible to prove his theory of gravitational waves.
“He famously thought these gravitational waves would be impossible to detect, but you and I live in the future, and we have really advanced technology that has enabled us to build an instrument like LIGO that’s capable of detecting gravitational waves, and using them to study the cosmos,” he said.
Einstein predicted the existence of gravitational waves in 1916 in his general theory of relativity. The mathematics indicated that massive bodies under acceleration, like binary black holes or the collapsing cores of huge stars in the death throes of supernova explosions, would radiate gravitational energy in the form of waves distorting the fabric of space-time.
The waves would spread out in all directions, traveling at or near the speed of light. By the time a wave from an event many light years away reached Earth, however, its effects on space-time would be vastly reduced, becoming hard-to-detect ripples rather than powerful waves.
And that makes detection a major challenge. Gravitational waves stretch and compress space over amazingly small scales by the time they reach Earth and to detect them, scientists and engineers had to devise a system that could measure changes in distance that are vastly smaller than the width of an atomic nucleus.
Each LIGO station features a pair of 2.5-mile-long vacuum tubes arranged in an L shape in which precisely tuned laser beams flash back and forth between multiple mirrors that effectively increase the distance each beam travels to nearly 1,000 miles. The laser beams then are recombined and directed into a sensor.
If the light from each vacuum tube travels exactly the same distance before it is recombined, the LIGO detectors will not “see” anything — the system is tuned so that the crests of light beams from one vacuum tube match up with the troughs of the other, creating destructive interference.
But according to Einstein, a gravitational wave will stretch space in one direction and compress it in a perpendicular direction. The effect on the LIGO stations would be to stretch the length of one vacuum tube and slightly shrink the other. Because the laser beams would travel slightly different distances during the passage of a wave, the crests and troughs would no longer match up when the beams are recombined.
The resulting interference pattern can be analyzed to determine exactly how much stretching and shrinking went on. But when it comes to gravitational waves, the effects on local space are truly infinitesimal, making detection a high-technology challenge and a feat Einstein could never have imagined.
To minimize the effects of sound-related vibrations, each vacuum tube in the LIGO system is pumped down to one-trillionth the pressure of Earth’s atmosphere at sea level. The resulting vacuum has eight to 10 times fewer atomic particles than the vacuum of space.
To eliminate vibrations from Earth sources, the 88-pound mirrors in the LIGO stations are suspended from the bottom of four pendulums, each using heavy counterweights. Computer controlled actuators damp out the largest vibrations before they can reach the pendulum-supported mirrors.
Finally, the LIGO system features two widely separated observing stations to make sure a local vibration is not misinterpreted. A gravitational wave should be seen by both stations at roughly the same time.
The LIGO equipment, recently upgraded to improve its sensitivity, is capable of detecting stretching and shrinking 10,000 times smaller than the width of a proton. That’s sensitive enough to measure the distance to the nearest star to within the width of a human hair.
On Sept. 14, 2015, the laser beams in the two LIGO facilities recorded just such a change.
Just as it took 100 years to prove Einstein’s theory correct, Larson said it could take just as long to figure out what impact the discovery might have on everyday life.
“Science is just now understanding this, and so we’re going to spend the next 100 years thinking hard about it, and maybe 100 years from now my and your great grandchildren will have some notion that this is important in their everyday lives,” he said.
Scientists have said LIGO or similar observatories might someday be able to detect gravitational waves created by the big bang birth of the universe.