For the first time in history, gravitational waves named BW150914 were detected using a Laser Interferometer Gravitational-Wave Observatory (LIGO) on Sept. 14, 2015, at 5:51a.m. by two LIGO detectors in Livingston, La., and Hanford, Wa. The LIGO Scientific Collaboration and Virgo Corporation made the discovery.
A team of 12 Georgia Institute of Technology (GT) faculty members, postdoctoral researchers and students, along with the LIGO Scientific Collaboration, announced their findings on Feb. 11, 2016. The team discovered that the waves were 1.3 billion years old and formed when two binary black holes merged. They compared the observation with theoretical predictions to confirm the discovery.
While the waves alone are a huge discovery, they in turn confirm Einstein’s theory of relativity. The discovery also creates endless possibilities for the universe.
Gravitational waves are described as ripples in the universe that bend and distort space-time by stretching and squeezing it as they travel. They are produced during violent cosmic disturbances, such as two black holes merging. This ties in to Einstein’s claim that space and time are curved by massive objects.
The two black holes were 29 and 36 times the mass of the Earth’s sun and produced a single, more massive spinning black hole. The gravitational waves were created a fraction of a second before the merger, and around three times the mass of our sun was converted to make the gravitational waves. The waves traveled at the speed of light and the waves’ recording lasted less than 200 milliseconds.
The GT team spent the next five months conducting various analyses to confirm and validate the gravitational waves and their source. They verified that the signal came from two black holes that were almost equal in mass and spinning on their retrospective axes.
Karan Jani, a fourth-year doctoral candidate in Georgia Tech’s Center for Relativistic Astrophysics (CRA) in the School of Physics, computed the distance to which LIGO detectors would be sensitive enough to record the black hole collision. When the waves were detected, it was a combination of the signal itself and background noise. One of the problems with the signal was the amount of noises that could influence the detectors and alter the data received.
“There are a lot of noises that can affect the detectors, such as wind or seismic activities,” said Karelle Siellez, a postdoctoral researcher in the School of Physics. “I joined the team called Detector Characterization where we worked on trying to understand all the noises.
My goal was to remove all the fake noises,” continued Siellez “We could not allow any kind of outside vibrations. We had to check everything to make sure that the trigger was correct.”
The group then examined the data from the LIGO detectors and, using matched-filtering, used models for gravitational wave signals to determine if the data contained a similar signal. They compared the waves with hundreds of simulations of binary black hole mergers, which was produced by the Georgia Tech numerical relativity team over years of research by solving Einstein’s equations on super-computers. This team is under the leadership of Dr. Deirdre Shoemaker, associate professor and director of CRA, who has spent the last 10 years researching massive black hole binaries.
“Since about 2005, theorists, including scientists at Georgia Tech, have been able to run very accurate super-computer simulations of black hole mergers,” said James Clark, a postdoctoral researcher in CRA. “This has let us develop very precise models for what we expect the gravitational wave signal to look like when two black holes collide. This also lets us demonstrate that the signal really does look exactly like we’d expect for a binary black hole system.”
Dr. Laura Cadonati, School of Physics assistant professor and chair of the LIGO Data Analysis Council, coordinated and guided hundreds of scientists around the world to analyze the data from the LIGO detectors.
“We looked for transient events in the data both in a search that made minimal or no assumptions on the signal, and also other searches based on the theoretical expectation of that the signals could look like,” said Cadonati. “We have matched the event to hundreds of theoretic waveforms to infer the size, distance and spin of the black holes.”
The overall confirmation all ties back to Albert Einstein, whose theory of general relativity was published in 1915. According to general relativity, two black holes orbiting each other lose energy through the emission of gravitational waves. This causes them to approach each other over the course of billions of years and finally merge. During the final fraction of a second in which the gravitational waves were created, the two black holes collided at nearly one-half the speed of light and formed a single massive black hole, converting their combined mass and energy, which is represented in the equation E = mc 2.. The energy is emitted as the gravitational waves.
As for the future of science, the waves contain information about their origins and the nature of gravity. They can help explain how the universe was created and evolved to this day, as well as provide news ways of exploring the universe and how it is divided.
“We will now learn about the universe in new ways, the least of which may be future discoveries of more black holes and neutron stars,” said Shoemaker. “We will get better tests of the theory of gravity and black holes. The most interesting may be what we cannot predict, the unknown we may discover. It amazes me what the human mind can do to understand the universe, but this is just the beginning.”
The waves also open a new field of gravitational wave astronomy, which can help scientists learn about the populations and lives of black holes and neutron stars as well as the birth of stars and the environments they form in.
“This is a big topic, and it’s going to take a long time to digest,” said senior lab coordinator and associate director of UWG Observatory Dr. Benjamin Jenkins. “It’s actually phenomenal because this is the first time that we have directly observed a black hole. We’ve been able to observe the effects of black holes before based on how stars go around them. This is the first time we’ve been able to observe them. This discovery is opening up a very wide range spectra for us to look at.”