Astrophysicists may have solved the mystery of disappearing stars

Instead of dying dramatically in a massive supernova explosion, some big stars can die quietly and without fanfare.

This could explain the mysterious and sudden disappearance of certain stars from the night sky noticed by astronomers over the years, according to a new journal article Physical examination letters.

These massive stars can completely collapse in on themselves and become black holes without a supernova, which was long thought to be a necessary part of the death of a large star.

An artist’s impression of the binary system VTFS 243, composed of a large star and a black hole. This black hole may have formed without a supernova, astronomers suggest.

ESOL. Calçada CC BY 4.0

Stars “burn up” through a process called nuclear fusion, which involves combining lighter hydrogen atoms into heavier helium, releasing vast amounts of energy in the form of light and heat. When this hydrogen fuel begins to run out, the star enters the later stages of its life and begins to die.

Stars can die in different ways depending on their mass. When stars run out of hydrogen, the star’s core contracts and heats, causing the outer layers to expand and cool, and the star becomes a red giant. Smaller stars – up to about 8 times the mass of our sun – will eventually expel these outer layers and the core will become a white dwarf. Larger stars, on the other hand, go through several stages of nuclear fusion, creating heavier and heavier elements until iron is produced, at which point nuclear fusion stops, the star collapses under its own gravity, and then explodes in a huge burst of energy known as a supernova.

If the remaining stellar core is between about 1.4 and 3 solar masses, it will collapse into a neutron star, an incredibly dense object composed mostly of neutrons, while if the core is more than about 3 solar masses, it will collapse into a black hole , a point in space with such strong gravity that even light cannot escape. from him.

However, this new research has found strong evidence that massive stars can die and form a black hole without any supernova at all, in a process known as “total collapse”.

“We believe that the core of a star can collapse under its own weight, as happens with massive stars in the last phase of their lives. But instead of the contraction culminating in a bright supernova explosion that would outshine its own galaxy, expected for stars more than eight times more massive than the Sun, the collapse continues until the star becomes a black hole,” study co-author Alejandro Viña- Gomez, a researcher at the Max Planck Institute for Astrophysics who was a postdoctoral fellow at the University of Copenhagen’s Niels Bohr Institute at the time of the study, said in a statement.

Black hole
Stock image of a black hole. Stars can form black holes without going supernova.

ISTOCK / GETTY IMAGES PLUS

According to the researchers, this discovery could also explain the phenomenon of stars that quietly disappear from the sky without an explosive supernova outburst.

“If one stood watching a visible star undergoing total collapse, it might, at just the right moment, be like watching a star suddenly extinguish and disappear from the heavens. The collapse is so complete that there is no explosion, nothing astronomers have actually observed the sudden disappearance of bright stars in recent times, but the results we obtained from the analysis of VFTS 243 bring us much closer to a credible explanation.” Viña-Gomez said.

This discovery was prompted by the observation of a binary star system called VFTS 243 in a small neighboring galaxy known as the Large Magellanic Cloud, which consists of a large star and a black hole with a mass about 10 times that of our sun.

This system should have traces of a star with a black hole that went supernova in the past, but astronomers could find no such evidence.

“Typically, supernova events in star systems can be measured in a variety of ways after they occur. But despite the fact that VFTS 243 contains a star that has collapsed into a black hole, traces of an explosion are nowhere to be found. “VFTS 243 is an extraordinary system that has barely changed since the collapse of the star into a black hole,” Viña-Gómez said.

Astronomers would expect to see signs of a “natal shock”, which is when a neutron star or black hole formed in a supernova is accelerated to between 100-1000 km per second by the massive forces of the supernova explosion. However, the black hole in the VFTS 243 system appears to have only been accelerated to about 4 km/s. Additionally, supernova forces typically affect the orbital symmetry of a binary star system, but no such effects have been observed in the VFTS 243 system.

“The VFTS orbit is nearly circular, and our analysis shows no signs of large asymmetries during collapse. This again shows the lack of an explosion,” Viña Gomes said.

Therefore, the black hole in the VFTS 243 system appears to have been born without a supernova.

“Our analysis points unequivocally to the fact that the black hole in VFTS 243 most likely formed instantaneously, with energy lost mainly via neutrinos,” co-author Irene Tambora, also a researcher at the Niels Bohr Institute, said in a statement

This discovery is expected to open new doors to the study of how stars die and how black holes are born.

“Our results highlight VFTS 243 as the best observable case yet for the theory of stellar black holes formed by total collapse where a supernova explosion fails, and which our models show to be possible. 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,” Tambora said.

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