Last year’s neutron-star collision that astronomers thought would have generated a black hole gave rise to a larger, hyper-massive neutron star instead.
It took astronomers one hundred years to finally detect gravitational waves that Einstein theorized in 1915.
Including the first discovery in 2016, scientists detected gravitational waves on seven occasions, the last of which was last year.
The LIGO and VIRGO observatories spotted this event on August 2017 — hence its name GW170817.
At first, scientists thought these gravitational waves originated from a Kilonova. They then thought that the event led to the formation of a black hole.
A Kilonova is an astronomical collision that involves either two neutron stars, or a neutron star and a black hole.
A new study, however, suggests the merger led to the formation of a hypermassive neutron star, or a magnetar.
The “multi-messenger” event that was GW170817 highlights the significance of multi-messenger astrophysics and gravitational wave astronomy.
An astronomical event or phenomenon is a “multi-messenger” when its study involves at least two different types of signals
In the case of the neutron star-crush from last year “observatories detected emission in gamma rays, X-rays, ultraviolet, visible light, infrared and radio waves – an unprecedented observing campaign that confirmed the location and nature of the source,” said researchers.
When the two astrophysicists reanalyzed GW170817 data from LIGO and VIRGO using a novel technique, they found a descending “chirp” that lasted 5 seconds that “started between the end of the initial burst of gravitational waves and a subsequent burst of gamma rays.”
This transient gravitational-wave chirp was 49 hertz to 1 kilohertz in frequency. This suggested its source could be a supermagnetic type of neutron star known as a magnetar rather than a stellar black hole like previously thought.
Hypermassive magnetars are nothing new to astronomers. However, inferring its nature here from the gravitational waves it originates is a first.
Van Putten, the paper’s co-author, noted that “we’re still very much in the pioneering era of gravitational wave astronomy. So it pays to look at data in detail. For us this really paid off, and we’ve been able to confirm that two neutron stars merged to form a larger one.”
A nascent field, gravitational wave astronomy will get another boost with the entry of the Kamioka Gravitational Wave Detector (KAGRA) in the Kamioka Observatory next year.