The fifth observation of gravitational waves (GW) marks the beginning of a new era in astronomy. On August 17, 2017, the LIGO and VIRGO collaborations detected neutron stars merging for the first time and immediately alerted observatories around the world. In a matter of hours the event had been located, another first for GW astronomy, and telescopes around the world begun studying it almost immediately.
The event observed, called GW170817, was produced in galaxy NGC 4993, located 130 million light-years from Earth. The gravitational signal was the strongest ever observed, lasting over 100 seconds, and it emitted a gamma-ray burst (GRBs), providing the first piece of evidence that GRBs are produced by neutron star collisions. It also provided the strongest evidence yet that neutron star mergers are responsible for the creation of the heaviest elements in the universe, like gold and platinum.
The importance of this observation cannot be overstated. We are witnessing Galileo pointing the telescope up, or Henrietta Swann Leavitt working out the relation that will be used to measure cosmic distances. This observation brings a completely new dimension to astronomy. The dozens of papers published in Nature, Nature Astronomy, Astrophysical Journal Letter, Science, and Physical Review Letters, are also record-breakers. They have over 45,000 authors – around 35 percent of all active astronomers in the world – who worked at the over 70 observatories that helped to make this discovery.
“Now we have the detection of not just the merger but the in-spiral motion of two neutron stars,” Dr Vicky Kalogera, the most senior astrophysicist in the LIGO Scientific Collaboration from Northwestern University, told IFLScience. “The signal we heard on August 17th is the strongest gravitational waves signal we have ever received and it is the longest. We have more than a hundred seconds. We detect the in-spiral motion very clearly until they merge. And this allowed us to measure the masses quite well.”
The merging neutron stars' masses are between one and two times the mass of our Sun, and the object they formed has a mass of between two and three solar masses. Theoretical predictions suggest black holes should form when neutron stars collide but researchers currently can’t confidently say if the remnant is a black hole or a neutron star.
The gravitational detection alone is enough to be incredibly excited about this discovery, but knowing that astronomers were able to detect the source using light telescopes makes this a pivotal moment in astronomy. One with very far-reaching consequences.