Neutron star collision creates gravitational waves. Source: Youtube / NASA Goddard
Scientists have made another monumental breakthrough that promises to revolutionise our understanding of the universe.
Overnight, international scientists announced they have detected, for the first time, gravitational waves created by the collision of two highly-dense neutron stars about 130 million light years away.
Gravitational waves are cosmic ripples in time and space, comparable to sound, that travel at the speed of light.
They were theorised by Albert Einstein a century ago but only physically recorded for the first time last year - a feat just acknowledged with the Nobel prize for physics.
This time, waves picked up in August alerted astronomers across the world to other signals, such as light, gamma rays and radio waves, also created by the same event.
Thousands of scientists, including those from the US-based Laser Interferometer Gravitational-Wave Observatory (LIGO); the Europe-based Virgo detector; and some 70 ground and space-based observatories were involved in piecing the picture together.
The breakthrough, just published in Physical Review Letters, Nature and Astrophysical Journal Letters, ultimately proved the first time that the collision of two neutron stars had been recorded.
Their collision also provided the loudest, closest and most precisely located gravitational wave signal yet received by humans.
Neutron stars are the smallest, densest stars known to exist - just a teaspoon of neutron star material has a mass of about a billion tonnes - and are formed when massive stars explode in supernovas.
As these neutron stars spiralled together, they emitted gravitational waves that were detectable for about 100 seconds; when they collided, a flash of light in the form of gamma rays was emitted and seen on Earth about two seconds after the gravitational waves.
In the days and weeks following the smashup, other forms of light, or electromagnetic radiation - including X-ray, ultraviolet, optical, infrared, and radio waves - were detected.
The LIGO data indicated that two astrophysical objects located at the relatively close distance of about 130 million light-years from Earth had been spiralling in toward each other.
It appeared that the objects were not as massive as binary black holes - objects that LIGO and Virgo have previously detected.
Instead, the inspiraling objects were estimated to be in a range from around 1.1 to 1.6 times the mass of the sun, in the mass range of neutron stars.
Graphic / LSC/Daniel Williams
While binary black holes produce "chirps" lasting a fraction of a second in the LIGO detector's sensitive band, the August 17 chirp lasted approximately 100 seconds and was seen through the entire frequency range of LIGO - about the same range as common musical instruments.
Scientists could identify the chirp source as objects that were much less massive than the black holes seen to date.
"It immediately appeared to us the source was likely to be neutron stars, the other coveted source we were hoping to see - and promising the world we would see," LIGO spokesman 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. It is a gift that will keep on giving."
The observations have also given astronomers an unprecedented opportunity to probe a collision of two neutron stars.
Australian National University astronomer Dr Christian Wolf said his team used their SkyMapper wide-field survey telescope and 2.3-metre telescopes as part of the search for other signals from the neutron star collision.
"We saw the light from a fireball blasting out from the neutron star collision into space in the hours and days afterwards," Wolf said.
"SkyMapper was the first telescope to report the colour of the fireball, which indicates the temperature of the fireball was about 6000C - roughly the surface temperature of the sun."
Auckland University astrophysicist Dr JJ Eldridge said the full story wasn't known yet.
"The observations are ongoing and only in the coming months and years will we really begin to fully understand how exciting this object is," Eldridge said.
"The fact that we have so much information from so many different sources will allow us to piece together in a way we have never been able to before. It's going to take a lot of time and a lot of effort."
Yet the event alone had already answered questions on the nature and structure of neutron stars - and confirmed that merging neutron stars appeared as a short gamma-ray burst and a type of explosion called a "kilonova".
"The observations of the kilonova, the explosive afterglow, also confirms something else," Eldridge said.
"In the explosion we have seen evidence for large amount of heavy elements."
These events mostly created elements such as gold, silver and platinum.
In this particular event, it was likely that hundreds or thousands of Earth-equivalent masses of gold and other elements were made.
