Astronomers think they may have found evidence of a very massive star star collapsing into a black hole instead of exploding as a bright supernova.
“If true, this would be the first direct detection of such a monster star ending its life in this manner,” said Andrew Allan, a PhD student at Trinity College Dublin, Ireland, and lead author of a new paper published today in the Monthly Notices of the Royal Astronomical Society.
What is a luminous blue variable star?
A luminous blue variable (LBV) star is a massive and unstable star some 2.5 million times brighter than the Sun that’s near the end of its life. Giant outbursts from LBVs are common, with their luminosity dramatically increasing. LBVs are also super-rare, hence the excitement about this one.
They’re poorly understood, largely because they’re so rare, and yet massive stars produce a significant proportion of the elements currently present in the Universe.
Where is the Kinman dwarf galaxy?
About 75 million light-years away in the direction of the constellation of Aquarius, the Kinman dwarf galaxy—also called PHL 293B—is blue compact dwarf galaxy.
It’s too far away for astronomers to see its individual stars. However, they can detect the signatures of some of the stars.
Who noticed the star is missing ?
Astronomers studied the massive star between 2001 and 2011 and concluded that it was in a late stage of its evolution—and destined to explode as a supernova—and when they returned to it in 2019 using the ESPRESSO and X-shooter instruments on the European Southern Observatory’s Very Large Telescope (VLT), its signatures were not present—it was missing.
“It would be highly unusual for such a massive star to disappear without producing a bright supernova explosion,” said Allan.
Why did the star disappear?
The scientists have two theories about why the star disappeared:
- A giant outburst by the star may have made it lose so much mass that it’s become a smaller, less luminous star.
- It may be less bright because it’s partially obscured by dust.
- The star collapsed into a black hole without producing a supernova.
As far as astronomers know, massive stars must end their lives as a supernova, so the latter would be a rare find.
Trouble is, there’s no evidence that it did go supernova, leaving the scientists puzzled.
“We may have detected one of the most massive stars of the local universe going gently into the night,” says team-member Jose Groh at Trinity College Dublin.
However, the also admit that the star’s disappearance could be explained by an undetected supernova explosion; the data collected between 2001 and 2011 may just be material ejected by a supernova interacting with deep space.
Why is this important?
Little is known for sure about how massive stars like this LBV die. Despite being 75 million light-years away, the Kinman dwarf galaxy is actually deemed to be in the “local Universe,” so this is essentially a close-up of a strange event.
It’s hoped that the ESO’s Extremely Large Telescope (ELT)—which will go live in 2025—will be able to directly resolve stars in distant galaxies like the Kinman dwarf galaxy, and shed some light on this cosmic mystery.
The researchers also suggest that the Rubin Observatory (formerly known as the LSST) sky survey due to go live later this year will be able to search for similar events.
Wishing you clear skies and wide eyes.