New Delhi: NASA’s Chandra X-ray Observatory has finally identified what has been triggering sudden, mysterious outbursts in a massive star in a distant galaxy. Researchers now suspect that a black hole, a neutron star, or another hidden space entity might be triggering these outbursts.
The findings were published on 9 November in The Astrophysical Journal by researchers at the Department of Astronomy, University of Virginia. The ‘star’ at the centre of the study, named AT 2016blu, is located nearly 30 million light-years away from the earth in a spiral galaxy called NGC 4559. The star, known among astronomers to be an LBV (luminous blue variable) is large, hot, and unstable, famous for the sudden changes in its brightness. Researchers have estimated that it has nearly 33 times the mass of the Sun.
“For 15 years, astronomers have been watching this star get really bright and then dim again on a regular basis. Until we were able to get Chandra data at the right time, we couldn’t figure out what was making this happen,” lead author Mojgan Aghakhanloo of the University of Virginia in Charlottesville told NASA.
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Bright outbursts
Chandra, named in the honour of the late Indian-American Nobel laureate Subramanyan Chandrasekhar, has now allowed scientists a better look at this mystery. Between 2012 and June 2026, astronomers had recorded at least 27 sudden outbursts from the star, roughly about one in every 113 days.
The brightness of the outburst made scientists suspect that they were supernovae, the explosions that mark the death of large stars. However, unlike any other supernova that dies after its last hurrah, AT 2016blu would survive, only to erupt again a few months later, making scientists call it a “supernova imposter”.
“This star’s behavior was confusing at first because it kept acting like a supernova, but clearly it’s not because it keeps surviving these outbursts about three times a year. To understand the cause of these eruptions, we realized we needed X-ray data, timed so that we’d observe the star when it was in an outburst,” said co-author Núria Torres-Albà, also of the University of Virginia.
Here is where Chandra played a key role. It is the only X-ray telescope that can differentiate between AT 2016blu and the other objects around it. Its observations hinted that the star’s eruptions might be linked to another celestial entity near it.
Scientists now predict that AT 2016blu is connected to this companion in an oval-shaped orbit. As the two come closer to one another, the companion pulls the gas and other material released by the star. When this material hurtles towards the companion, it heats up, producing X-rays and heating up the dense gas around, making it glow.
Researchers are now calling AT 2016blu the first known star of its kind to have a companion that leads to such reactions. A better understanding of AT 2016blu could help scientists understand other such massive stars that experience similar sudden changes in brightness.