Last Monday scientists announced the first observation of two neutron stars colliding, as well as the observation of the gravitational waves it created. The event happened 130 millions light-year away in the galaxy NGC 4993.
A neutron star is what is left after the collapse of a normal star but which is still too light to become a black hole.
A neutron star is about the same size as London, and yet it is one of the densest of celestial bodies in the universe. If you could take a teaspoon of a neutron star and weigh it, it would weigh the same as 100,000 Eiffel Towers, or a billion tonnes. They are so dense that it is probable the two stars collapsed into a black hole.
When two such neutron stars collided, on the 17th of August at 12:41 GMT, multiple observatories simultaneously detected gravitational waves from this event for 100 seconds. Then two seconds after, a flash, and after that, over a number of days, X ray, ultraviolet and infrared radation were detected from the place the event occurred.
A gravitational wave is a vibration of space-time caused by an event that involves dense objects such as neutron stars and black holes. Although they have been theorised by Albert Einstein, it was only in 2015 that we made our first observation of them by using the Laser Interferometer Gravitational-Wave Observatory (LIGO) detector. The detector uses a system of two lasers that cross with a mirror and when a gravitational wave comes by, the laser helps us see it because their signal is disturbed.
The Nobel Price of physics 2017 was awarded to Rainer Weiss, Barry C. Barish and Kip S. Thorne, the three scientists who contributed to the LIGO detector. They are to whom we owe our ability to observe gravitational waves.
This is the fifth time that gravitational waves have been detected. But this is the first time the event that allowed us to detect those waves was originating from two neutron stars colliding. It was said to be “the most intensely observed astronomical event to date”. It is the first time that we were able to know where in the sky the event that created a lot of gravitational wave happened and turn the telescopes towards it.
A dozen papers were published today as a result of the discovery. It is described by Professor Matthew Bailes, the director of the ARC Centre of Excellence for Gravitational Wave Discovery, speaking at press conference on the discovery, as having “hailed a new era in astronomy” and that “the avalanche of science is unparalleled in modern astrophysics”.
This observation is truly important for several reasons. First, it confirms that the speed of gravitational waves is equivalent to that of light, which scientists had theorised but needed confirmation.
Secondly, this observation will help to develop new ways to measure the expansion of the universe. According to Matthew Bailes, if astronomers are able to observe a lot of events like this, they will be able to describe the rate at which the universe is expanding.
Lastly, there’s confirmation that heavy metals such as gold and platinum, the origins of which for decades have eluded scientists, are forged when neutron stars such as the ones observed collide, as the immense pressures and forces push lighter elements together, forming heavier elements.