Astronomers identify 1st twin stars doomed to collide in kilonova explosion

Massive stars typically end in dramatic explosions, but occasionally they fade out like ineffective fireworks.

One such failed firework has been located by astronomers at SGR 0755-2933, a neutron star located 11,400 light-years from Earth in the Puppis constellation. According to recent findings, this star transmitted extraordinarily large quantities of mass to its binary companion early in its existence, leaving it without enough material for an explosive demise. Instead, it came to a silent conclusion as a "ultra-stripped" supernova, a rare cosmic occurrence that leaves a neutron star as its super-dense afterlife.

According to André-Nicolas Chené, an astronomer at the NOIRLab research facility of the National Science Foundation and a co-author of the new study, "this amazing binary system is basically a one-in-10-billion system."

The neutron star is the first obvious example of a star system that will eventually result in a kilonova, a cosmic explosion in which two neutron stars merge. The kilonova will be caused by the neutron star and its closely orbiting binary companion, a star that the researchers also predict will eventually collapse to become a neutron star.

Despite a kilonova being discovered for the first time in 2017, scientists could only record the event's aftermath at the time due to measurements of light and gravitational waves. For the first time, according to the recent research, astronomers have located a binary star system that will eventually explode in a kilonova.

Furthermore, it was previously believed by scientists that spiral galaxies like our Milky Way would only include one or two such systems. The current study's researchers have raised that estimate to 10, saying that these data aid in their understanding of the background, evolution, and unusually peaceful deaths of stars in such systems.

In the release, Chené added that scientists have long conjectured about the precise circumstances that would someday result in a kilonova. These new findings show that it is possible for two sibling neutron stars to combine when one of them was formed without a typical supernova explosion, at least in some circumstances.

It has a name like a license plate: CPD-29 2176. The sister star is big, circles the primary neutron star every 60 days, and is massive. The most recent study's researchers looked to this sibling star to learn more about how the present star system came to be and what may happen to it in the future.

This is not only a straightforward binary system.

While looking through data gathered by the Cerro Tololo Inter-American Observatory in Chile, Clarissa Pavao, an undergraduate student at the Embry-Riddle Aeronautical University in Arizona, discovered the system. She was specifically mapping the twin star's spectra, which is an examination of how much light a star produces at various wavelengths. She found one straightforward line in the spectra after removing noise from the data, indicating the huge star had a nearly circular orbit, which is rare for binary star systems.

The initial neutron star's demise as a failed supernova was determined by this crucial discovery, according to the researchers.

Normally, mass transfer starts when one of the stars in a binary system burns up its hydrogen and approaches the end of its main-sequence stage. Companion stars are frequently forced out of the systems and onto highly elliptical orbits by the ensuing end-of-life explosion.

But the fascinating system does not appear to have experienced this. Astronomers combed through tens of thousands of binary star system models that resembled SGR 0755-2933 in order to better comprehend what may have happened at the conclusion of the star's existence. Only two of the matches were discovered.

After tracing the star's history, the researchers came to the conclusion that it behaved essentially like any other big star running out of fuel: Near the end of its life, the star started transferring mass to its partner and eventually became a low-mass star with a helium core, as predicted. Noel Richardson, an astronomer at Embry-Riddle and the lead author of the new study, said in a statement that because the star lost so much mass during this process, its end-of-life supernova "didn't even have enough energy to kick the orbit into the more typical elliptical shape seen in similar binaries."

According to the study, the two stars still maintain close orbits because the fading star did not have enough energy to expel its partner from the system.

introducing valuable heavy metals into the world

The new discovery will aid astronomers in understanding the origins of some of the heaviest atoms in our universe, in addition to learning more about kilonova occurrences.

Only a few million years have passed since the silent supernova, and scientists predict that the CPD-29 2176 system will continue to exist in its current form for at least another million years. According to their simulations, the sister star would ultimately undergo an ultra-stripped explosion and collapse into a neutron star, much like the original neutron star.

The research anticipates that the two neutron stars would gently drift toward one another in a cosmic dance millions of years from now, eventually meeting in a kilonova explosion. According to Richardson, these explosions are known to be the source of enormous amounts of heavy materials including platinum, xenon, uranium, and gold "that get thrown into the universe."

Heavy metals produced during such catastrophes are thought to have hung in the interstellar medium until they formed asteroids, which subsequently impacted Earth as it developed and left behind the valuable metals we see today. It appears that a failed supernova isn't as detrimental to the cosmos as previously thought. The 2017 kilonova event alone released at least 100 Earth's worth of priceless heavy metals into space.

The research is described in a paper