Last October 16, 2017, astronomers made a universe-shaking announcement about the detection of reverberations from the collision of two neutron stars.
It is another triumph for LIGO, short for Laser Interferometer Gravitational-Wave Observatory, the instrument that has opened a new window into the universe by detecting shakings in the fabric of space-time known as gravitational waves.
Previously, LIGO, had detected three mergers of black holes. Scientists who helped create LIGO also just won the Nobel Prize in Physics.
The new discovery sheds light on a smaller, different type of rumbling, one that can be both seen and heard. Here are answers to some questions you might have about the discovery.
What’s a neutron star?
Let’s back up a step: what’s a neutron? An atom consists of a heavy center known as the nucleus, surrounded by a cloud of tiny negatively charged electrons.
In the nucleus are two types of particles: positively charged protons and electrically neutral neutrons.
A neutron star, as its name suggests, is a star that consists almost entirely of neutrons.
Here’s how that neutron star formed:
For most of their existence, stars emit light through fusion the merging of hydrogen atoms into helium, which releases gargantuan amounts of energy.
When a large star probably at least six times the mass of the sun exhausts its hydrogen, it begins to collapse.
The collapse accelerates so quickly that it sets off cataclysmic explosion known as a supernova. What’s left over is an extremely dense cinder that is only about six miles wide, but packs in more mass than the sun.
The pressure is so great that electrons and protons are squeezed together into neutrons.
A single thimbleful of a neutron star weighs as much as several million elephants.
How does a neutron star differ from a black hole?
A neutron star is a stellar cinder that stopped collapsing.
But when even larger stars explode, the remaining core is so dense that the core continues collapsing until it turns into a black hole. Here’s our guide to black holes.
What happens when two neutron stars collide?
In the case of the discovery that was detailed last October 16, 2017, the merging objects were probably survivors of massive stars that had been orbiting each other and had each puffed up and then died in spectacular supernova explosions.
Making reasonable assumptions about their spins, the astronomers calculated that these neutron stars were about 1.1 and 1.6 times as massive as the sun, smack in the known range of neutron stars.
As they approached each other, swirling a thousand times a second, tidal forces bulged their surfaces outward. Quite a bit of the material was ejected and formed a fat doughnut around the merging stars.
At the moment they touched each other, a shock wave squeezed more material out of their polar regions, but the doughnut and extreme magnetic fields confined the material into an ultra-high-speed jet emitting a blitzkrieg of radiation.
That blast set off the gravitational waves detected by LIGO, as well as the light show spotted by a variety of telescopes.
What are gravitational waves?
Watch this video we made in 2016 when LIGO first detected them to learn more about these ripples in space-time that confirmed key aspects of Albert Einstein’s theories.
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Pass it on: New Scientist