In recent years, astronomers have been investigating an unusual phenomenon: stars seemingly disappearing, leaving few clues as to why they disappeared from our view.
In 2019, the Vanishing and Appearing Sources during a Century of Observations (VASCO) project attempted to catalog how many stars have disappeared from view over the past 70 years and found about 100 that had vanished without concrete explanation.
Stars can dim like Betelgeuse or explode like a supernova before collapsing into a black hole or neutron star, but generally don’t just disappear from view.
“In the delayed neutrino-driven mechanism, neutrinos revive the stalled shock wave, ultimately leading to a successful explosion,” writes the author of a new study. ‘In this case, the stellar mantle is successfully ejected and the remnant of the compact object is in most cases a neutron star (NS). However, if the explosion mechanism fails, the continued accretion of matter on the temporarily stable proto-NS pushes the latter beyond its mass limit and a black hole (BH) forms.
Smaller stars take longer to use up their fuel. Our own sun (a yellow dwarf) will become a red giant when it depletes its supply of hydrogen, and then a small white dwarf when it depletes its supply of helium. These tiny remnants – made up mainly of carbon and oxygen – could eventually collapse into theoretical black dwarf stars, although there hasn’t been enough time in the universe for this to happen yet.
So why do some stars just seem to disappear? One possible explanation, tentatively supported by evidence in a new study, is that stars with enough mass can collapse into a black hole without going supernova – turning directly into a black hole, without a massive explosion taking place . to expect.
The team looked at a binary star system on the edge of the Milky Way, known as VFTS 243, consisting of a main sequence O star and a trailing hole that orbit each other every 10.4 days. The team tried to look for signs that the black hole formed after a supernova explosion, including baryonic mass ejecta and “natal kicks” that accelerate orbiting objects.
“In the extreme scenario of complete collapse into a BH, ejecta mass and birth kicks are assumed to be very low,” the team explains in their paper. “In this case, mass energy is lost via neutrinos and, to a lesser extent, gravitational waves. This differs from the archetypal scenario in which anisotropic baryonic ejecta are the main carriers of momentum.”
The team found evidence for the idea that the black hole formed with little baryonic ejecta, suggesting it could have formed through a total collapse.
“Our calculations provide constraints on the total birth kick and mass loss, which we find are largely consistent with mass loss solely from neutrino emission and an associated birth kick,” the team wrote, “rather than baryonic mass ejecta” .
While cool in itself, the team raised the possibility that this could explain the sudden disappearance of some (major) stars.
‘If one were to stare up at a visible star undergoing a total collapse, it could, at just the right moment, be like watching a star suddenly extinguish and disappear from the sky. The collapse is so complete that no explosion occurs, nothing happens. escapes and you wouldn’t see a single bright supernova in the night sky,” Alejandro Vigna-Gómez, co-author of the study, said in a statement. ‘Astronomers have actually observed the sudden disappearance of brightly shining stars in recent times. We cannot be sure of a connection, but the results we obtained from the analysis of VFTS 243 have brought us much closer to a credible explanation.”
As always, further research is needed, but the observations are quite exciting.
“Our results highlight VFTS 243 as the best observable case yet for the theory of stellar black holes formed by total collapse, where the supernova explosion fails and which our models have shown is possible,” says Professor Irene Tamborra of the Niels Bohr Institute. co-author of the study, added. “It’s an important reality check for these models. And we certainly expect the system to serve as a crucial benchmark for future research into stellar evolution and collapse.”
The study has been published in the journal Physical Review Letters.