A team of scientists just announced a groundbreaking discovery that encompasses everything from Albert Einstein's theories about the laws of physics to the fundamental way we approach our study of the universe.
On Thursday at a news conference in Washington, D.C., the LIGO Scientific Collaboration, made up of more than 1,000 scientists worldwide, publicly released results that had been secretly circulating among the scientific community for the past few weeks: the first detection of a phenomenon called gravitational waves that came from two colliding black holes.
This is the first time humans have detected the merging of two black holes, and it is also themost compelling evidence we now have that black holes truly exist.
Black holes are a mysterious breed of cosmic beast whose gravitational pull on their surrounding environment is so great that nothing escapes — not even light.
This makes them impossible to see with the naked eye, difficult to detect, and even tougher to study. As a result, black holes continue to boggle the minds of the most brilliant astrophysicists.
But now, thanks to a $620 million machine called Advanced LIGO, short for Laser Interferometer Gravitational-Wave Observatory, astrophysicists have a new tool to spy on these elusive creatures.
Briefly described in an email by McMaster University physicist Clifford Burgess and leaked to Twitter earlier this month — and now detailed in a paper published in Physical Review Letters— the LIGO Collaboration found evidence of two gigantic black holes spiraling toward each other, eventually merging into a single, more monstrous black hole.
So, why does this matter, and what do gravitational waves have to do with it?
Well, gravitational waves are the sole means today's scientists have to observe a black-hole merger. Without them, we would have no way of knowing whether mergers actually exist.
"If this is true," Burgess told Science Magazine about the discovery before Thursday's announcement, "then you have 90% odds that it will win the Nobel Prize in Physics this year. It's off-the-scale huge."
Detecting the unthinkably tiny
In 1916, Einstein first predicted that when two bodies accelerate through space around each other, they produce ripples of energy in the form of what experts call gravitational waves. These waves then propagate away from the source at the speed of light and, eventually, reach Earth.
As these waves travel, they contract and expand the fabric of spacetime — like ripples across a pond. But these distortions are extremely small — as much as one-millionth the width of a hydrogen atom.
These gravitational waves would be so minuscule, Einstein thought, that humans could never actually detect them.
His skepticism held true for a century.
But Advanced LIGO is an ingenious tool in the hunt for gravitational waves.
Here's how it works:
- It uses a highly sophisticated laser system (shown to the right) that's sensitive to distortions about 10-18 meters — small enough to catch a gravitational wave.
- It consists of two detectors — one in Livingston, Louisiana, and the other in Hanford, Washington. This way, the signal seen from one detector can be confirmed or denied fairly quickly by the second detector. And as the scientists reported on Thursday, they saw the same signal at both detectors.
- At each detector, engineers fire a powerful laser into something called a beam splitter, which separates the laser into two beams. The resulting beams travel back and fourth across two tunnels, each 2 1/2 miles long, with a mirror at the end. The beams reflect off the mirror and eventually converge back at the center. When they do that, the beams recombine and, essentially, disappear. But this disappearing act can occur only if the two beams take the same amount of time to return from their journey down the two tunnels.
Here's the key part: If a gravitational wave were to get in the way of one of the beams, the beams would create a flash of light upon recombination because one beam takes longer to return than the other, messing up the disappearing process.
That flash of light is what the LIGO collaboration has been after for the past 14 years.
Simple math for a complex problem
From this signal, the scientists were able to deduce that what they were seeing was a cosmic collision of epic proportions.
That collision involved two black holes, one 36 times as massive as our sun and the other 29 times as massive, spiraling toward each other in a rapid, cosmic dance, 1.3 billion light years away.
In line with a prediction by Einstein, as the two closed in, they emitted increasingly more frequent gravitational waves.
This translated into a higher pitch in the LIGO signal, with the climax happening at the time the two black holes merged. The result was a high-pitched "whoop!" that experts call a "chirp" and that sounds like this:
The pitch of the "whoop" gives scientists an idea of what they're seeing, explained Szabolcs Marka, a Columbia University physics professor and member of the LIGO collaboration.
"We can categorize them well enough so when we see a signal we can fingerprint it," Marka told Business Insider. "We can say that this must have been a supernova [or] this must have been two black holes ... because they kind of sound different."
By studying the final sound, the scientists calculated the mass of the final black hole, and what they discovered was a black hole 62 times as massive as our sun. But the initial masses, 36 and 29, do not add up to 62; three solar masses were missing.
The team reported that this extra mass was radiated away in the form of energy-carrying gravitational waves.
Now, that is a whopping amount of energy. To compare, theoretical physicist Luboš Motl calculated that the sun and the Earth emit enough energy in the form of gravitational waves (yes, the Earth emits these waves too) to charge two Edison light bulbs. These two black holes emitted 1044 times as much energy as that.
This is the first time in history that humans have ever seen two black holes merge. Before now, astronomers couldn't be sure whether such an epic collision ever occurred because they had no way of detecting it.
Scientists will continue to ramp up the sensitivity on Advanced LIGO over the next five years. By 2020, scientists suspect its sensitivity will increase by 1,000 times, which will improve their chances of catching more gravitational waves in the near future.
Also joining in this hunt, eventually, are the advanced Virgo interferometers located at the European Gravitational Observatory in Italy and the Kamioka Gravitational Wave Detector at the Kamioka Mine in Japan, set to begin operations in 2018.
"It is good to be a scientist," Marka said.