Although massive stars usually die with spectacular explosions, a handful fizzle out like misfire firecrackers.
Astronomers have identified the remains of such a failed firecracker in SGR 0755-2933, a neutron star about 11,400 light-years from Earth in the southern constellation of Puppis. In new research, scientists say that earlier in life, this Star transferred abnormally high amounts of mass to its binary companion – so much so that it did not have enough material left for an explosive death. Instead, it ended in a quiet “ultra-stripped” supernovaa rare cosmic event that leaves in its wake a super-dense residue called a neutron star.
“This remarkable binary system is essentially one in 10 billion,” said André-Nicolas Chené, an astronomer at the National Science Foundation’s NOIRLab research center and co-author of the new study. statement.
Related: Right place, right time: The Hubble telescope captured a supernova as it exploded
The neutron star and its close-orbiting binary companion — a star that researchers also predict will one day collapse to become a neutron star — mark the first clear example of a star system that will eventually spark a kilonovaa cosmic explosion in which two neutron stars merge.
Although a kilonova was first detected in 2017, astronomers then only recorded the aftermath of the event, thanks to observations of light and gravitational waves. The new research is the first time scientists have identified a binary star system that they know will end in a kilonova explosion.
Moreover, astronomers previously thought that only one or two of these systems would exist in spiral galaxies like ours. Milky Way. The researchers in the latest study have now raised that estimate to 10, noting that these observations help them better understand the history, evolution and atypically quiet death of stars in such systems.
“For some time, astronomers have speculated about the exact conditions that could possibly lead to a kilonova,” Chené said in the statement. “These new results demonstrate that, in at least some cases, two sister neutron stars can merge when one of them was created without a classic supernova explosion.”
The sister star is massive, orbits the primary neutron star every 60 days, and has a license plate-like name: CPD-29 2176. Scientists behind the latest research studied this star sister to understand the formation of the current star system. like what might unfold in his future.
“It’s not just a simple binary system”
Clarissa Pavao, an undergraduate student at Embry-Riddle Aeronautical University in Arizona, discovered the system while browsing through data captured by the Cerro Tololo Inter-American Observatory in Chile. In particular, she plotted the spectra of the sister star, an analysis of the amount of light emitted by a star at particular wavelengths. After cleaning up the noise from the data, she noticed a single line in the spectra that suggested the massive star had a very circular orbit – an unusual feature in binary star systems.
It was a key discovery that helped the team conclude that the primary neutron star ended in a failed supernova, the astronomers said.
Usually when one of the stars in a binary system burns up its hydrogen and is nearing the end of its main sequence stage, it begins to transfer mass to its companion star. The resulting end-of-life explosion often ejects companion stars from systems and places them in highly elliptical orbits.
But that doesn’t seem to have happened in the intriguing system. To better understand what might have happened at the end of SGR 0755-2933’s life, astronomers combed through thousands of models depicting binary star systems resembling the one they were studying. They only found two matches.
The team then traced the star’s history and concluded that it behaved, for the most part, like any other massive star that had run out of fuel: towards the end of its life, the star began to transfer mass to its companion and shrunk into a low-mass star. with a helium core, as scientists expected. In the process, however, the star lost so much mass that its late-life supernova “didn’t even have enough energy to launch the orbit into the more typical elliptical shape seen in similar binaries”, Noel Richardson, an Embry-Riddle astronomer and lead author of the new study, said in a statement.
The dying star also didn’t have enough energy to push its companion out of the system, which is why the two stars continue to have close orbits, according to the study.
In addition to learning more about kilonova events, the new research will help astronomers better understand the origins of some of the heaviest elements in our universe.
The silent supernova occurred only a few million years ago, and astronomers expect the CPD-29 2176 system to remain as it is for at least a million years. Their models show that, just like the primary neutron star, the sister star will then become an ultra-stripped supernova and eventually collapse into a neutron star.
Millions of years from now, the team predicts the two neutron stars will slowly spin toward each other in a cosmic dance, eventually colliding in a kilonova explosion. Such explosions are known to be a The source huge amounts of heavy elements like platinum, xenon, uranium and gold “that are being thrown out into the universe,” Richardson said.
Astronomers have long suspected that the heavy metals released in such events hovered in the interstellar medium until they coalesced into asteroids, which then bombarded Earth as it formed and deposited the precious metals we see. today. The kilonova 2017 event alone shipped at least 100 precious metals for Earth, so it seems a failed supernova isn’t such a loss to the universe after all.
The research is described in a paper (opens in a new tab) published Wednesday, February 1 in the journal Nature.
Follow Sharmila Kuthunur on Twitter @Sharmilakg. Follow us on twitter @Spacedotcom and on Facebook.