Astrophysicists may have solved the mystery of disappearing stars

Rather than dying dramatically in a massive supernova explosion, some large stars may die quietly and without fanfare.

This could explain the mysterious and sudden disappearance of certain stars from the night sky that astronomers have noticed over the years, according to a new article in the journal Physical Assessment Letters.

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

Stars “burn” through a process called nuclear fusion, which combines lighter hydrogen atoms into heavier helium, releasing a huge amount of energy in the form of light and heat. When this hydrogen fuel runs 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 up, causing the outer layers to expand and cool, and the star becomes a red giant. Smaller stars – up to about eight times the mass of our Sun – will eventually push out 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 increasingly heavier elements until iron is made. At that point, the 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 has 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 has more than about 3 solar masses, it will collapse into a black hole . , a point in space with a gravitational force so strong that not even light can escape. of it.

However, this new research has found strong evidence that massive stars can die and form a black hole without going supernova, in a process known as ‘complete collapse’.

‘We believe that a star’s core can collapse under its own weight, as happens with massive stars in the final stages of their lives. But instead of the contraction culminating in a bright supernova explosion that would outshine its own galaxy, as expected for stars more than eight times more massive than the Sun, the collapse continues until the star becomes a black hole,” says co-author Alejandro Vigna-Gómez, researcher at the Max Planck Institute for Astrophysics, who was a postdoc at the University of Copenhagen. Niels Bohr Institute during the investigation, said in a statement.

According to the researchers, this finding could also explain the phenomenon of stars silently disappearing from the sky without the explosive burst of a supernova.

‘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. 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,” Vigna-Gómez 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 ten times that of our sun.

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

‘Normally, supernova events in galaxies can be measured in different ways after they have occurred. 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 nowhere to be found. an extraordinary system The orbit of the system has hardly changed since the collapse of the star into a black hole,” said Vigna-Gómez.

Astronomers had expected to see signs of a ‘natal kick’, that is when a neutron star or black hole formed in a supernova is accelerated to between 100 and 1000 km per second by the immense forces of the supernova explosion. However, the black hole in the VFTS 243 system appears to have only accelerated to about 4 km/s. Furthermore, supernova forces usually affect the symmetry of the orbit of a binary star system, but no such effects were observed in the VFTS 243 system.

“The orbit of VFTS is almost circular and our analysis indicates that there are no signs of major asymmetries during the collapse. This again indicates the absence of an explosion,” said Vigna Gomez.

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

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

It is hoped that this discovery will open new doors for studying 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 the supernova explosion fails and which our models have shown is possible. 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,” Tamborra said.

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