A star masquerading as a supernova for 15 years is actually an unstable star. Located 25 million light-years away, AT 2016blu fooled astronomers since January 11, 2012. Mojgan Aghakhanloo said, "For 15 years, astronomers have been watching this star get really bright and then dim again on a regular basis."

A star that has been masquerading as a supernova for the last 15 years is actually a hot, luminous, and unstable star. The revelation comes from NASA's Chandra X-ray Observatory. The cosmic imposter in question is AT 2016blu, which has fooled astronomers into thinking it was a supernova explosion on January 11, 2012. It is located on the outskirts of spiral galaxy NGC 4559 some 25 million light-years away in the constellation Coma Berenices.

Astronomers were baffled by AT 2016blu's behavior, as the star kept getting bright and then dimming again every 113 days.

Mojgan Aghakhanloo from the University of Virginia in Charlottesville said, For 15 years, astronomers have been watching this star get really bright and then dim again on a regular basis.

The team suspected that X-ray data would help explain these eruptions.

Aghakhanloo's team used Chandra to observe an outburst of AT 2016blu in March 2026.

The observatory detected a powerful blast of X-rays during this false supernova outburst.

These observations revealed that AT 2016blu has an unseen companion, either a neutron star or a stellar-mass black hole, on an elliptical orbit around it.

This discovery suggests that AT 2016blu was once part of a binary star system.

The companion's gravity pulls material from the unstable star

, triggering its brilliant outbursts.

This material forms an accretion disk around the neutron star or black hole, emitting X-rays.

These high-energy emissions heat up a cloud of gas ejected by the luminous blue variable years ago, making it glow brightly in visible light and creating the illusion of a supernova.

The companion of AT 2016blu is likely a black hole or neutron star, both remnants of massive stars that have gone supernova.

The intense X-ray emissions from the compact object heat the surrounding gas cloud, causing it to glow brightly in visible light.

This effect creates the illusion of a supernova explosion when in fact it is just an outburst from this unstable star and its hidden companion.