Tag: Neutron Star

It Was A Universe-Shaking Announcement. But What Is A Neutron Star Anyway?

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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Neutron Star Smash-Up Produces Gravitational Waves And Light In Unprecedented Stellar Show​

The 2015 detection of gravitational waves – ripples in the very fabric of space and time – was one of the biggest scientific breakthroughs in a century.

But because it was caused by two black holes merging, the event was all but invisible, detectable indirectly via the LIGO facility.

Now a team of scientists has announced the fifth detection of gravitational waves, but there’s a groundbreaking difference this time around.

The ripples were caused by the collision of two neutron stars, meaning the event was accompanied by light, radio, and other electromagnetic signals for the first time.

First predicted by Albert Einstein over 100 years ago, gravitational waves are caused by cosmic cataclysms like the collision of two black holes, but because of the immense distance.




By the time they reach us here on Earth the distortions are occurring on the subatomic scale.

To observe waves that tiny, LIGO beams lasers down a 4-km (2.5-mi) long tunnel and measures how gravitational waves might warp the beam as they wash over our local corner of spacetime.

That delicate process is effective at confirming the phenomenon, but still somewhat indirect.

This is the first time that the collision of two neutron stars has been detected, and this is the closest and most precisely located gravitational wave signal we’ve received,” says Susan Scott, the Leader of the General Relativity Theory and Data Analysis Group at Australian National University (ANU), which played a key role in the observation.

It is also the loudest gravitational wave signal we’ve detected.

The collision occurred in a galaxy called NGC 4993, which lies about 130 million light-years away – that might sound far, but it’s much closer than previous observations, which occurred at distances of billions of light-years.

As well as producing gravitational waves, the neutron stars’ collision sent a host of electromagnetic signals sweeping across the universe, including a short gamma ray burst, X-rays, light and radio waves.

These were picked up by observatories all over the world, helping pinpoint the source.

ANU was among those, using SkyMapper and the Siding Spring Observatory in New South Wales, Australia, to observe the brightness and color of the light signals given off.

Along with learning more about gravitational waves, the discovery can teach astronomers about neutron stars.

Created when larger stars collapse, neutron stars are relatively tiny – only about 10 km (6.2 mi) wide – and incredibly dense, with very strong magnetic fields. Other than that, not a whole lot is known about them.

With this discovery we have the opportunity to learn so much more about neutron stars, which have been quite a mystery to us,” says Scott.

Unlike black holes, neutron star collisions emit other signals such as gamma rays, light and radio waves so astronomers around the world were able to observe the event through telescopes. This is an amazing time to be a scientist.

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Pass it on: New Scientist