An ultra-rare star system is a giant space accident waiting in the wings

(ORDO NEWS) — For the first time, astronomers have positively identified a binary system destined to one day become a kilonova, the explosive result of neutron star collisions.

And, ironically, the key ingredient to that possible fate is a pair of failed, failed supernovas.

This phenomenon is considered so rare that there are only about 10 such binary systems in the entire Milky Way. A closer look at this system should help scientists understand how these crazy events play out.

“For a long time, astronomers have speculated about the exact conditions that could eventually lead to a kilonova,” says astronomer André-Nicolas Chenet. from NOIRLab.

“These new results demonstrate that, at least in some cases, two sister neutron stars can merge when one of them was created without a classic supernova explosion.”

Neutron Stellar collisions are rare, but they play an important role in populating the universe with heavy elements such as gold, platinum and uranium.

These elements cannot be created inside stellar cores; the energy required for stellar nucleosynthesis of elements heavier than iron is greater than the energy produced by this nucleosynthesis, resulting in a disorderly end of the star.

Instead, these elements are formed in energetic events such as kilones: we have evidence for this from GW170817, the historic neutron star collision observed by telescopes around the world.

But these events are rare and therefore rather mysterious. We have only seen a handful of neutron star mergers and have never before found a system destined to become one.

Enter a binary system called CPD-29 2176, consisting of a neutron star and a type of massive blue star called the Be star, located about 11,400 light-years from Earth. Be stars have features in their light that indicate the presence of disk-shaped material around them.

They also frequently appear in binary systems with neutron stars, emitting X-rays as a neutron star passes through them. disk surrounding a Be star.

When the bright X-ray flare was observed from the same part of the sky as the Be star in CPD-29 2176, astronomers Noel Richardson and Clarissa Pavao of Embry-Riddle Aviation University took a closer look, eventually identifying some of the light not emitted by the Be star. It was a neutron star.

They were also able to calculate the orbit of the binary system. And then everything became interesting. Because this orbit was unusually round, unlike the more elliptical orbits commonly seen in such binaries.

This was the irrefutable evidence that led the researchers to conclude that the neutron star was born from a “failed” supernova. – also known as a supernova supernova.

Normally, when a massive star goes supernova, it ejects its outer material in a spectacular explosion, while the remaining core collapses into a neutron star an ultra-dense object about 2.4 times the mass of the Sun, packed into a sphere just 20 kilometers (12 miles).

In an ultrapure supernova, there isn’t enough outside material left to explode into space. Instead, the core collapses with little fanfare. This appears to have happened to CPD-29 2176.

“The star was so depleted that the explosion did not have enough energy even to bring the orbit to the more typical elliptical shape seen in similar binary systems. ‘ says Richardson.

So where did all this stuff go? When the neutron star reached the end of its life, it became puffy, and its outer shell was within the gravitational reach of the Be star, which engulfed it.

By the time the star had turned into a neutron star, it was completely stripped, stripping it of material that would otherwise produce supernova fireworks.

Eventually, the Be star will also end its life as a neutron star, resulting in a binary neutron star in a decaying orbit that will one day cause a neutron star collision, the two of which merge to form either a large neutron star or a black hole.

“The current neutron star should have formed without throwing its companion out of the system. A supernova supernova is the best explanation for why these companion stars are in such a narrow orbit,” says Richardson.

“In order to create a kilonova one day, another star must also explode as a supernova so that the two neutron stars can eventually collide and merge.”

However, this day is still far away. Star Be still has at least a million years left before its inevitable transformation. And the slow inspiration for a possible merger could take millions more.

But with the identification of CPD-29 2176, astronomers have a new piece of the puzzle that could help identify other similar systems among the Milky Way’s billions of stars.

“This system reveals that some neutron stars are formed in a small supernova explosion,” says Richardson.

“As we understand the growing population of systems such as CPD-29 2176, we are getting an idea of ​​how peaceful the death of some stars can be. and whether these stars could die without traditional supernovae.”


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