When massive stars die as we understand the universe, they don’t go away quietly. When they run out of fuel, they become unstable, rocked by explosions before finally ending their lives in a spectacular supernova.
But scientists found that some massive stars simply disappeared without leaving a trace in the night sky. Stars clearly visible in the older surveys are inexplicably absent in the newer ones. The star isn’t exactly a set of keys—you can’t just lose it on the back of the couch. So where the hell do these stars go?
A new study has given us the most convincing explanation yet. According to an international team led by astrophysicist Alejandro Viña-Gómez of the Niels Bohr Institute in Denmark and the Max Planck Institute for Astrophysics in Germany, some massive stars may die, ultimately not with a bang, but with a whimper.
Their evidence? A binary system called VFTS 243 in the Large Magellanic Cloud consisting of a black hole and a companion star. This system shows no signs of a supernova explosion, which according to our models should have accompanied the formation of the black hole.
“If one were to stand and watch a visible star go through total collapse, it could, at just the right moment, be like watching a star suddenly go out and disappear from the heavens,” Viña-Gómez explains.
“The collapse is so complete that there is no explosion, nothing comes out, and one would not see a bright supernova in the night sky. 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 brought us much closer to a plausible explanation.”
When a star more massive than about 8 times the mass of the Sun goes supernova, it’s extremely confusing. The outer layers—most of the star’s mass—are explosively ejected into space around the star, where they form a vast, expanding cloud of dust and gas that remains for hundreds of thousands to millions of years.
Meanwhile, the star’s core, no longer supported by the outward pressure of fusion, collapses under the influence of gravity to form an ultradense object, a neutron star or a black hole, depending on the star’s initial mass.
These shrunken nuclei do not always remain stationary; if the supernova explosion is tilted, it can eject the core into space in a natal impact. Sometimes we can also trace the core’s trajectory back to the cloud of material that was ejected as it died, but if enough time has passed, the material may have dissipated. But signs of labor can last much longer.
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VFTS 243 is a very interesting system. It consists of a massive star that is about 7.4 million years old and about 25 times the mass of the Sun, and a black hole about 10 times the mass of the Sun.
Although we can’t see the black hole directly, we can measure it based on the orbital motion of its companion star—and, of course, we can infer other things about the system.
One interesting thing is the shape of the orbit. It’s almost round. This, along with the system’s motion in space, suggests that the black hole did not receive a massive supernova blow. The researchers who discovered the black hole in 2022 suspected as much; now the work of Viña-Gómez and his colleagues has confirmed it.
There is growing evidence to suggest that sometimes massive stars can collapse directly into black holes without going supernova or collecting 200 cosmic dollars. VFTS 243 represents the best evidence we have for this scenario to date.
“Our results highlight VFTS 243 as the best observable case so far for the theory of stellar black holes formed by total collapse where a supernova explosion fails, and which our models have shown to be possible,” says astrophysicist Irene Tambora of the Nils Bohr Institute.
“This is an important reality check for these models. And we certainly expect that the system will serve as a crucial benchmark for future studies of stellar evolution and collapse.”
The study was published in Physical examination letters.
