Neutron Stars

Gravitational Waves Detected from Two Colliding Neutron Stars

It’s been few days, still, we could not possibly forget the recent achievement, the observation of the two neutron stars colliding, for the first time in the history of mankind. Many theories have been proposed over the year on how the event takes place, but this time we have successfully detected as well as observed the merger of two neutron star. On Aug. 17, the LIGO and Virgo team detected a gravitational-wave signal having an incredible amount of energy coming from two colliding neutron stars, the superdense remnants of stars after they have collapsed. The event has been marked as GW170817.

Neutron Stars
The kilonova on the first day of discovery, and four days after, as seen by the Las Campanas Observatory. (Credit: Carnegie Institution for Science)
Neutron Stars
(Click to enlarge)

It was Albert Einstein who first proposed the idea of gravitational waves in 1916, as distortions in the space-time fabric triggered by violent cosmic events like the merger of black holes or neutron star. We have been able to detect four gravitational waves event. But until now there was no confirmed detection having a visible signature on the sky. The primary reason is quite simple, the earlier four detections were triggered due to collisions (or mergers) between binary black holes, which don’t emit any light. Another reason was lack of detectors. With the two LIGO’s detectors in Livingston, Louisiana and Hanford, Washington, it was not possible to pinpoint the events in the sky. The addition of Virgo’s interferometer in Italy, improved the location accuracy a lot (x10).

What are gravitational waves and how are they detected? A GRAVITATIONAL WAVES 101 course from National Geographic.

The story of this exceptional detection is quite fascinating. It was morning at 8:41 am ET on August 17. Scientists and Engineers were a bit frustrated after an unproductive month of a long run. Just before both LIGO and Virgo were scheduled to stop observation, LIGO’s observatories in Washington and Louisiana detected a gravitational wave signal. The wave perturbed their instrument over a minute and a half, which leads to the conclusion about its source. The merging objects are much smaller than black holes. Around 1.7 seconds later, NASA’s Fermi Gamma-ray Space Telescope and ESA’s INTErnational Gamma Ray Astrophysics Laboratory, picked up an intense gamma-ray burst from the same area of sky. Laura Cadonati, a LIGO collaborator, and professor of physics at Georgia Institute of Technology tells The Verge, “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.”

The new observation was made possible because of the efforts of 70 ground- and space-based observatories along with LIGO and Virgo. They focused on a small area of the sky in the constellation of Hydra, next to the lenticular galaxy NGC 4993.

Neutron Stars
An all-sky map shows the confirmed detections of gravitational waves to date. Click to enlarge. (Credit: Leo Singer | Axel Mellinger | LIGO | VIRGO | NASA)

The event has several characteristics to be explored, that gives the opportunities to the observatories and institutions around the world, to publish papers. Not to mention this year the lead scientists have been awarded the Nobel Prize in physics.

LIGO spokesperson David Shoemaker said, “From informing detailed models of the inner workings of neutron stars and the emissions they produce, to more fundamental physics such as general relativity, this event is just so rich.”

Source: The Verge, ScienceAlert, National Geographic, Space

Sayan is a theoretical physicist from Plasma Science discipline. He is a front-end developer with an eye for details and a passion for perfection. He enjoys writing popular science articles and taking part in discussions.