The discovery first began with an epic cosmic collision over a billion years ago…
Today is a big day for science. An international team of researchers with the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) announced the detection of gravitational waves.
The results have been speculated for months, and the team is predicted to be a shoo-in for the Nobel prize. Before they could share these exciting results with the world, the team had to be sure of their findings. After months of checking and double checking, the team revealed the historic findings to the public during a press conference at the National Press Club in Washington, DC this morning. The team announced that on September 14, 2015 LIGO’s twin interferometers, located in Livingston, Louisiana and Hanford, Washington, were the first to directly detect gravitational waves.
“To make this fantastic milestone possible took a global collaboration of scientists — laser and suspension technology developed for our GEO600 detector was used to help make Advanced LIGO the most sophisticated gravitational wave detector ever created,” says Sheila Rowan, professor of physics and astronomy at the University of Glasgow.
To fully understand the implications of this discovery, let’s look back, a long time ago, in a galaxy far, far, away. This may sound like the opening to Star Wars, but it’s also the prelude for one of the greatest scientific discoveries in recent times.
The discovery first began with an epic cosmic collision over a billion years ago, in a galaxy more than one billion light-years from Earth. In that galaxy, a pair of black holes (called a binary pair) were locked into an orbital dance. Spiraling around a common barycenter, the duo consisted of two stellar mass black holes with a mass of 29 and 36 times more massive than the Sun, respectively. These cosmic heavyweights, both about the size of the metropolitan area of Washington, DC eventually merged, resulting in a violent explosion that sent ripples in the very fabric of space and time speeding through the Universe at nearly the speed of light.
These ripples, known as gravitational waves, were first predicted by Albert Einstein in 1916 as an expansion of his theory of general relativity, and resemble the ripples produced when a rock disturbs a pond. According to general relativity, space and time are not two separate things, but instead are like a massive singular fabric called space-time.
Imagine you and some friends were each holding a corner of a giant sheet and place a bowling ball on it, the sheet will curve under the bowling ball. The same thing happens in space. Massive objects like stars, and black holes distort space-time, causing planets and even light to curve around the massive objects.
“The description of this observation is beautifully described in the Einstein theory of general relativity formulated 100 years ago and comprises the first test of the theory in strong gravitation. It would have been wonderful to watch Einstein’s face had we been able to tell him,” said Ranier Weiss of MIT.
The notion of gravitational waves takes the warping of space-time one step further by saying if space-time can bend, it can also ripple or oscillate. Previous studies have confirmed the existence of gravitational waves, but LIGO is the first to directly detect this cosmic phenomenon.
“Our observation of gravitational waves accomplishes an ambitious goal set out over five decades ago to directly detect this elusive phenomenon and better understand the universe, and, fittingly, fulfills Einstein’s legacy on the 100th anniversary of his general theory of relativity,” added Caltech’s David H. Reitze, executive director of the LIGO Laboratory.
Spotting these elusive signals is no easy feat. Unlike light, gravitational waves are not disrupted by massive objects. As the wave passes through the Earth, it squeezes space-time in one direction, while stretching it in another direction. LIGO’s twin interferometers are 4,000 kilometers apart and each contain two arms that are 400 kilometers in length. The two arms are joined to form an “L-shape”. At the joint, a beam of light is shot down each arm where it bounces off a mirror, and races back to the starting point. The beams produced a predictable pattern that will be distorted if a gravitational wave passes through it. If the same distortion pattern is observed at both detectors, then the researchers can be confident the signal is real.
In this case, the distortion was less than the width of a human hair. Let that sink in for a minute. Incredible, right?
“Almost everything we currently know about the universe has been discovered with light of some kind,” said Vicky Kalogera, director of Northwestern’s Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). “Gravitational waves carry completely new information about black holes and other cosmic objects and will unlock a new window onto the universe. These waves are very weak and challenging to detect, but now we have detected our first burst of gravitational waves.”
The discovery of gravitational waves is opening a new era of astronomy, one in which we will we able to see and hear the Universe. LIGO is like a stethoscope, searching for the heartbeat of the Universe. “We can hear gravitational waves,” LIGO research scientist, Gabriela Gonzalez said during the press conference. “We can hear the Universe. That’s one of the best things about this. We will not only see the Universe, we are going to be listening to it.”
As the gravitational wave passed through the detectors, a pulse approximately 20 milliseconds in length was recorded. The pulse or chirp was so short that the team had to exaggerate it in order to properly hear it. “What we have done is taken the real signal and shifted it a bit in frequency,” explained Gonzalez. “But it is the real signal.”
This discovery really took a village…a global village. LIGO recently resumed operations following a series of upgrades. Many nations helped in the development of the technology within the two detectors and an international team of scientists deciphered the data. Europe, Japan, and even India have plans to build their own versions of LIGO. When all four locations come online, we will not only be able to detect gravitational waves, but also pinpoint where they originate from with incredible precision.
“Hopefully this first observation will accelerate the construction of a global network of detectors to enable accurate source location in the era of multi-messenger astronomy,” says David McClelland, professor of physics and director of the Center for Gravitational Physics at the Australian National University.