A neutron star collision created a neutron star we thought was too heavy to exist

(ORDO NEWS) — The flash of light emitted by colliding neutron stars has once again turned our understanding of how the universe works.

An analysis of the short gamma-ray burst that erupted from the merger of two stars showed that, sooner than a black hole was formed, as expected, the direct product of the merger was a highly magnetized neutron star, much heavier than the calculated maximum mass of a neutron star.

This magnetar apparently survived for more than a day before breaking apart. down into the black hole.

“It is generally believed that such a massive neutron star with a long lifespan is impossible,” astronomer Nuria Jordana-Mitzjans from the University of Bath in the UK told The Guardian. “It’s a mystery why this one was so long-lived.”

Neutron stars are on the spectrum of how a star might end up at the end of its life. For millions or billions (or perhaps trillions) of years, the star will chug, the engine fusing the atoms in its hot, pressurized core.

In the end, the atoms that the star can fuse will run out, and at that moment, point, everything kind of explodes. The star ejects its outer mass and, no longer supported by the external pressure generated by fusion, the core collapses under the internal pressure of gravity.

How we classify these collapsed cores depends on the mass of the object. The cores of stars, which originally had a mass of about 8 times the mass of the Sun, collapse into white dwarfs, the upper limit of the mass of which is 1.4 solar masses, compressed into a sphere the size of the Earth.

The cores of stars with masses between 8 and 30 solar masses turn into neutron stars with masses between 1.1 and 2.3 solar masses in a sphere only 20 kilometers (12 miles) in diameter.

And the largest stars, exceeding the upper mass limit of a neutron star, collapse into black holes, according to the theory.

But there is a very noticeable disadvantage of black holes with a mass less than 5 solar masses, so what happens in this mass mode? is largely a mystery.

This is why neutron star mergers are so interesting to astronomers. They occur when two neutron stars are in a binary system and reach the point of orbital decay, at which they inevitably merge together and become one object that unites the two neutron stars.

Most binary neutron stars have a combined mass that exceeds the theoretical upper mass limit for neutron stars. Thus, the products of these mergers are likely to sit firmly within this neutron star-black hole mass gap.

When they collide, binary neutron stars emit a burst of high-energy radiation known as short gamma rays. – beam explosion. Scientists thought they could only be emitted during the formation of a black hole.

But exactly how merging neutron stars turn into a black hole remains a mystery. Does a black hole form instantly, or do two neutron stars produce a very heavy neutron star, which then collapses into a black hole very quickly, no more than a few hundred milliseconds after the merger?

GRB 180618A was a short-lived gamma-ray burst discovered in June 2018, light that took 10.6 billion years to reach us. Jordana-Mitzjans and her colleagues wanted to take a closer look at the light emitted by this object: the burst itself, the kilonova explosion, and the long-lived afterglow.

But when they looked at the electromagnetic radiation caused by the event over time, something was wrong.

The optical emission of the afterglow disappeared 35 minutes after the gamma-ray burst. The team found that this was due to the fact that it was expanding at close to the speed of light accelerated by a continuous source of energy.

This corresponded not to a black hole, but to a neutron star. And not just a neutron star. It looked like it was what we call a magnetar: a magnetic field 1,000 times stronger than that of an ordinary neutron star, and a quadrillion times stronger than that of the Earth. And it hung for over 100,000 seconds (almost 28 hours).

“For the first time,” says Jordana-Mitzjans, “our observations revealed multiple signals from a surviving neutron star that survived at least one day after the death of the original binary neutron star.”

What could have helped the magnetar to live so long is unclear. Perhaps the magnetic field helped him a little, creating an external attraction that prevented him from being completely destroyed, at least for a while.

Whatever the mechanism, it will definitely happen. require further study – the group’s work shows that supermassive neutron stars are capable of firing short-term gamma-ray bursts, and that we can no longer assume the presence of a black hole.

“Such conclusions are wrong. important because they confirm that newborn neutron stars can power some short-lived gamma-ray bursts and their accompanying bright emissions in the electromagnetic spectrum,” says Jordana-Mitzjans.

“This discovery could offer a new way of detecting neutron star mergers, and therefore sources of gravitational waves, as we search the sky for signals.”


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