An exploding star in a distant spiral galaxy has baffled astronomers by surviving 27 violent outbursts over 14 years, revealing itself to be a rare stellar impostor powered by a hidden binary companion.
Automated supernova surveys originally flagged the object, designated AT 2016blu, when it flared in 2016. Located in the spiral galaxy NGC 4559 roughly 30 million light years away, the star possesses about 33 solar masses. Unlike genuine supernovae that destroy themselves in a single terminal blast, this massive star repeats its volatile display every 113 days. Universe Today reported that automated sky surveys first discovered the object in 2012.
Chandra X-Ray Observatory Detections
To uncover the mechanism behind these recurring eruptions, researchers coordinated targeted observations using the National Aeronautics and Space Administration’s Chandra X-ray Observatory. Because Chandra features exceptional angular resolution, it successfully isolated AT 2016blu from a much brighter nearby ultraluminous X-ray source, NGC 4559 X7.
The European Space Agency’s XMM-Newton observatory had previously observed the region four times while studying the neighboring source, but lacked the X-ray power to resolve the individual stellar impostor.
“For 15 years, astronomers have been watching this star get really bright and then dim again on a regular basis,” said Mojgan Aghakhanloo, a Virginia Institute of Theoretical Astronomy Origins Fellow at the University of Virginia in Charlottesville, told Universe Today. “Until we were able to get Chandra data at the right time, we couldn’t figure out what was making this happen.”
Accretion-Powered Outbursts
The research team tracked 27 optical outbursts from the luminous blue variable between 2012 and June 2026. By timing Chandra observations to coincide with a predicted visual flare in March 2026, scientists captured X-ray data showing the source was 100 times brighter than archival data from 2001 and 2002. Co-author Nathan Smith of the University of Arizona in Tucson explained the mechanics driving the phenomenon to Universe Today.
“We suspected that the bright repeating flashes at optical wavelengths might actually be powered by periodic blasts of high-energy X-rays,” said Smith, told Universe Today. “The dense gas surrounding the system is heated by the X-rays and then glows in the optical. So, we needed to plan the Chandra X-ray observations carefully to be simultaneous with an optical outburst.”
The Binary Companion Hypothesis
According to research published in The Astrophysical Journal, the system consists of an eccentric binary orbit. The primary star is a luminous blue variable exceeding 33 solar masses, while the secondary object is likely a neutron star or a black hole. As both stars traverse their eccentric orbits, the primary ejects material that forms an accretion ring around the compact companion, generating intense X-rays.
“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,” said Núria Torres-Albà of the University of Virginia, told Universe Today. Researchers estimate that roughly 2.7 percent of Earth’s mass transfers during each periastron passage.
Expanding the Transient Sample
Scientists ruled out alternative explanations, such as a coincident background quasar, by analyzing stacked archival Chandra images captured prior to the first documented outburst. The discovery marks the first observationally known luminous blue variable system featuring a compact companion. Researchers aim to locate similar objects to clarify the evolutionary pathways linking supernova impostors with interacting stellar explosions.
