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Investigating the disappearance of a massive star in a distant galaxy

This illustration shows what the luminous blue variable star in the Kinman Dwarf galaxy could have looked like before its mysterious disappearance.
This illustration shows what the luminous blue variable star in the Kinman Dwarf galaxy could have looked like before its mysterious disappearance. (L. Calçada/ESO)

A massive star has quietly disappeared in a dwarf galaxy 75 million light-years away, according to a new study. Given the lack of a visible supernova, the researchers believe the star grew dim and was obscured from view by dust or reached the end of its life and collapsed into a black hole.

"If true, this would be the first direct detection of such a monster star ending its life in this manner," said Andrew Allan, study author and doctoral student at Trinity College Dublin in Ireland, in a statement.

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

Previously, astronomers studied and observed the star between 2001 and 2011. Those observations helped determine that the star was in the later stage of its evolution and lifetime. Allan and his colleagues wanted to observe the star to further their research about how massive stars come to an end.

The astronomers used the European Southern Observatory's Very Large Telescope in Chile last year, but they couldn't spot the mysterious and unstable star, which is located in the Kinman Dwarf galaxy.

"Instead, we were surprised to find out that the star had disappeared!" Allan said.

A fading star

Although the star is at such a distance that it's difficult to discern the signals of individual stars, this blue star was 2.5 million times brighter than the sun. Luminous blue variable stars are unstable and can shift in brightness — but even then, they leave a traceable calling card for astronomers.

But even this signal was missing in 2019.

"It would be highly unusual for such a massive star to disappear without producing a bright supernova explosion," Allan said.

The team used different instruments in hopes of detecting the star's signal, but they found nothing.

"We may have detected one of the most massive stars of the local Universe going gently into the night," said Jose Groh, study coauthor and director of astrophysics and tenured assistant professor at Trinity College Dublin, in a statement.

The effects of volatility

The team also looked back at archival data of the star taken in 2002 and 2009, which suggested the star may have experienced a period of strong outbursts after 2011. This activity, which contributes to the lack of stability of luminous blue variable stars, can increase their luminosity as well as their rate of mass loss.

Based on this data, it's possible that the outburst may have dimmed the star and obscured it from view with dust, the researchers believe. But it's also possible that the star collapsed into a black hole.

Future telescopes, like the European Southern Observatory’s Extremely Large telescope coming online in 2025, can study distant stars in more detail and provide more information about this stellar mystery.