Once again, scientists have spotted gravitational waves, which are essentially ripples in the fabric of space and time created by objects moving through the universe. However, this time it's different and grand. This time around, the celestial signal stems from an event, which has never been seen before - the merger of two neutron stars. Unlike the prior detections of gravitational waves, this time the event was noticeable by regular light telescopes.
While previous gravitational waves, which were detected by scientists, were created from the mergers of black holes, the latest event occurred from the violent collision of two distant neutron stars. It was visible on Earth via regular light telescopes because, after getting together, these two objects rapidly twirled around each other in space and then smashed into each other, creating a massive fireball of light, which was caught by the telescopes, said the researchers.
Three gravitational observatories on Earth detected the signal in August 2017 - dual US-based observatories operated by LIGO and the one located in Italy, Virgo. After getting the information from these observatories, astronomers pointed out the location where the merger took place. They narrowed it down to a rather small patch of the southern sky.
Once the general area was spotted, LIGO spread the information to the astronomy community across the globe and within just a few hours of the detection, thousands of astronomers operating across about 70 ground-based and space-based telescopes started searching the sky. Eventually, they located the explosive leftovers of the merger, pointed out The Verge.
While until now, the light was the only source that the scientists could use to study object in space, now they will be able to do so using light as well as gravitational waves, which marks a new era known as "multi-messenger astronomy."
"This is a revolution in astronomy, of having thousands of astronomers focus on one source for weeks and having this collaboration unravel in seconds, in hours, then days, and weeks. For us, that's the Holy Grail," said Vicky Kalogera, an astrophysicist at Northwestern University and one of the LIGO collaborators, to The Verge.
The first gravitational wave was detected two years ago. Ever since they were first predicted by legendary theoretical physicist Albert Einstein in his theory of relativity, astronomers have been trying to detect these ripples for the last century. While the first detections of gravitational waves were made by LIGO observatories, the fourth signal one was caught by Virgo as well.
The fifth gravitational waves detection was announced on October 16 by the National Science Foundation (NSF). On August 17 at 8:41 AM ET, both the LIGO observatories in Washington and Louisiana picked up a signal of what appeared like gravitational waves. While the previous signals had lasted for just a fraction of a second, this time it prevailed over a minute and a half. From this, the astronomers immediately suspected that these waves are the result of a merger of two objects that are much smaller than black holes.
"Neutron stars are so much smaller than black holes, so they get much closer together before they merge. So you can observe the waves for a long time, and get a nice, long, beautiful signal," Laura Cadonati, a LIGO collaborator and professor of physics at Georgia Institute of Technology, told the publication.
NASA's Fermi telescope also received a signal of an intense explosion of high-energy light, gamma ray burst, coming from deep space. This made the astronomers more confident about the fact that they were, indeed, witnessing a collision of two neutron stars.
In the meantime, the astronomers thought that Virgo observatory had missed the signal, as it was not visible in the observatory's data. Upon another look, scientists realized that Virgo had also picked it up but the signal was extremely faint, as the merger took place at a location in the sky, which, due to its location, is kind of a blind spot for the observatory. "Virgo in a way missed it, because it happened to be in a narrow part of the sky where Virgo couldn't quite catch it," said Kalogera.
However, the fact that Virgo couldn't notice it properly helped the astronomers in locating the exact point in space. They knew that it must be the part of the southern sky which Virgo cannot see. Five hours later, Virgo and LIGO shared a sky map with a general location with the astronomers around the world and seven hours from then the leftovers of the collision was spotted and the source of the gravitational waves was finally established, stated the report.
Swope observatory (ground-based) in Chile first saw it and snapped its images in visible lights. After that other ground- and space-based telescopes started discovering it.
Las Cumbres Observatory Global Telescope Network was also one of the first observatories that noticed this celestial event. Andy Howell, an astronomer from this observatory told The Verge, "This is the reason we all become scientists. There's nothing like the feeling knowing you're one of the first people in the world to see a new phenomenon."
According to the data gathered by LIGO, from this phenomenon, the two neutron stars were combined at a distance of 130 million light-years away from Earth, which much closer compared to the black hole mergers that occurred billions of light-years beyond our globe. It has also been revealed that each of the neutron stars was between 1.1 and 1.6 times the mass of Sun, reported the publication.
The impact of the merger is called kilonova, an enormously explosive event. This collision, apart from providing data on gravitational waves, may have also given an insight into how the heaviest elements were produced in the universe. The light emitted from the kilonova made it visible how those elements, such as gold, were produced in the wake of the merger.
"Theorists have been working on kilonova for the past decade, and now with this one singular event, all this decade of work is all kind of coming to a head," Tony Piro, principal investigator of the Swope Supernova Survey, told The Verge. "It's really a momentous event."