For decades, astronomers have been puzzled by the sudden disappearance of stars from the night sky. Normally, stars either gradually dim or explode in spectacular supernovae if they are massive enough. However, over the past 70 years, astronomers have recorded at least 800 instances of stars vanishing without any warning.
In some cases, observers noted the presence of a star one hour, only to find it completely gone the next. This mystery has left scientists scratching their heads – until now.
A new study led by astronomers at the University of Copenhagen and published in the journal Physical Review Letters offers an explanation. The research suggests that these stars might be collapsing directly into black holes due to their incredible mass. This process would cause them to disappear instantly without leaving any trace.
Alejandro Vigna-Gómez, a co-author of the study from the Niels Bohr Institute, explained the phenomenon.
"If someone were to watch a star going through a total collapse, it might seem like the star suddenly extinguishes and vanishes from the heavens," he said. "The collapse is so complete that no explosion happens, nothing escapes, and there would be no bright supernova in the night sky."
Normally, when a massive star, at least eight times heavier than our Sun, dies, it collapses under its own gravity, leading to a supernova explosion. This explosion releases so much energy that it can outshine its entire galaxy. Following this, the star typically becomes either a black hole or a neutron star.
However, the researchers propose that in some cases, this explosive phase is bypassed entirely. Instead, a sufficiently massive star collapses straight into a black hole. While this "total collapse" theory isn't new, the researchers have provided some of the most compelling evidence to date.
Their findings are based on observations of a binary star system named VFTS 243. In this system, a star ten times the mass of our Sun orbits a black hole. This system is exceptional because it shows almost no evidence of a supernova explosion.
"The orbit of the system has barely changed since the collapse of the star into a black hole," Vigna-Gómez noted.
Typically, when a star explodes as a supernova, it experiences a "natal kick" – an acceleration caused by the mass it ejects into space. However, the astronomers found no signs of such a kick in the VFTS 243 system. The orbits of the star and black hole were undisturbed, suggesting that most of the energy was lost through subatomic particles called neutrinos, which interact very weakly with gravity.
Although more research is needed to confirm these findings, they provide an important check on current models of stellar evolution, said Irene Tamborra, another study co-author from the Niels Bohr Institute. "We expect this system will serve as a crucial benchmark for future research into stellar evolution and collapse," she added.
