Monster star mysteriously disappears, scientists suspect it turned into black hole without going supernova

It would be highly unusual for such a massive star, 2.5 million times brighter than the Sun, to disappear without producing a bright supernova explosion, say the authors

                            Monster star mysteriously disappears, scientists suspect it turned into black hole without going supernova
(ESO/L Calçada)

Stars end their lives with a bang, exploding violently into the night. But one massive star -- 2.5 million times brighter than the Sun -- seems to have bucked the trend. It disappeared without notice, leaving no clues about its whereabouts, according to a new study. Reporting the missing star were researchers from the UK, US, and Chile. After looking into the case, these experts suspect the stellar object collapsed into a black hole, without blowing up. "It would be highly unusual for such a massive star to disappear without producing a bright supernova explosion," Andrew Allan, a PhD student from Trinity College Dublin and the lead author of the study, says. They also have another theory: the disappearance could be due to cosmic dust, which may have blocked its visibility.

The star is question is located in the Kinman Dwarf galaxy, about 75 million light-years away. It is classified as a luminous blue variable, objects known for their exceptional size and brightness. But their brightness fluctuates, making them highly unstable. Despite that, this star produced distinct signatures of its presence, until 2019. The highly unstable monstrous star has been on the team's watch for many years. "We had this star on our shortlist since it was located in a distant galaxy where stars could die differently than in our Milky Way," team-member Dr Jose Groh, also of Trinity College Dublin, tells MEA WorldWide (MEAWW). Their suspicion turned out to be true. "We were fortunate to catch the disappearance," he adds.

Can stars turn into black holes without exploding into a supernova? 

According to Dr Groh, computer modeling has predicted that some stars will not produce a bright supernova when they die. "This happens when a massive black hole is formed, and it is not spinning very fast. This could well be the case of this monster star in the Kinman galaxy," he explains.

Image of the Kinman Dwarf galaxy [NASA, ESA/Hubble, J Andrews (U Arizona)]

In reality, astronomers believe they have recorded one such instance. In the galaxy NGC 6946, about 22 million light-years away, a smaller massive star seemed to have vanished without a bright supernova explosion. But the stellar object in Kinman Dwarf galaxy is different: it is more massive and is located in a dwarf galaxy, Dr Groh explains. The event could hold clues on how stars collapse to a black hole without exploding.

What about the dust theory?

Dr Groh and his team investigated the role of cosmic dust in the star's disappearance. Using Very Large Telescope, located in the Chilean Atacama Desert, and others elsewhere, the team analyzed data gathered on the stellar object over the years and compared them. "The ESO Science Archive Facility enabled us to find and use data of the same object obtained in 2002 and 2009," says Andrea Mehner, a staff astronomer at ESO in Chile who participated in the study.

Based on their analysis, the team predicted that the star was undergoing a powerful outburst shortly before its disappearance. "Because of their extreme conditions, such as high temperature and density, stars close to the end of their lives become very unstable. So we have a strong suspicion that the outburst is potentially the swan song for this star before quietly collapsing to a black hole," Dr Groh adds. In the future, the team hopes to study the star's fate using a more sophisticated European Southern Observatory's Extremely Large Telescope (ELT). It is set to begin operations in 2025 and is capable of resolving stars in distant galaxies such as the Kinman Dwarf.

The study is published in the journal Monthly Notices of the Royal Astronomical Society.

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