The artistic impression of the luminous blue variable star that mysteriously disappeared. Image title (Credit: ESO / L. Calçada)
In 2019, scientists witnessed a massive star that disappeared without a trace 2.5 million times brighter than the sun.
Now, in a new article published today (June 30) in the Monthly Notices of the Royal Astronomical Society, a team of space detectives (see: astrophysicists) are trying to solve the case of the missing star by providing several possible explanations. Of these, a twist ending stands out: Perhaps, the researchers wrote, the massive star died and collapsed into a black hole without first experiencing a supernova explosion, a truly “unprecedented” stellar act of suicide.
“We may have detected one of the most massive stars in the local universe by stepping gently into the night,” Jose Groh, an astronomer at Trinity College Dublin and co-author of a new article on the star, said in a statement.
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“If true, this would be the first direct detection of a monstrous star ending its life this way,” study lead author Andrew Allan, also of Trinity College, said in the statement.
The star in question, located about 75 million light-years away in the constellation Aquarius, was well studied between 2001 and 2011. The bloated orb was an excellent example of a luminous blue variable (LBV): a massive star that near the end of its life and prone to unpredictable variations in brightness. Stars like this are rare, with only a handful confirmed in the universe so far. In 2019, Allan and his colleagues hoped to use the Very Large Telescope of the European Southern Observatory to learn more about the mysterious evolution of the distant LBV, only to discover that the star had apparently completely disappeared from its host galaxy.
Normally, when a star much larger than our sun reaches the end of its life, it explodes in a huge supernova explosion. These explosions are easy to detect as they stain the sky around them with ionized gas and powerful radiation for many light years in all directions. (Sometimes this looks downright beautiful.) After the explosion, the dense core of the leftover stellar material can collapse into a black hole or neutron star, two of the most massive and mysterious objects in space.
The missing LBV left no such radiation. It just disappeared.
To investigate this mystery, the researchers analyzed previous observations of the star taken in 2002 and 2009. They discovered that the star had experienced a strong period of explosion during this time, throwing huge amounts of stellar material at a much faster rate than usual . . LBVs can experience multiple outbursts like this in their temperamental old age, the researchers wrote, making them shine much brighter than normal. The outbreak probably ended sometime after 2011, the team said.
This could explain why the star seemed so bright during those first observations; however, it does not explain what happened after the blast that made the star disappear. One explanation could be that the star dimmed considerably after its explosion, and was then obscured by a veil of cosmic dust. If this were the case, the star could reappear in future observations.
The strangest and most exciting explanation is that the star never recovered from its explosion, but instead collapsed into a black hole without becoming a supernova. This would be a rare event, the team admitted. Given the star’s estimated mass before its disappearance, it could have created a black hole that measured 85 to 120 times the mass of Earth’s sun, though how this could have happened without a visible supernova remains a question. open.
Additional observations of the distant star-eating galaxy are required before this case can be officially closed.
Originally published in Live Science.
