Stellar Outbursts in NGC 4559
Astronomers using NASA’s Chandra X-ray Observatory have identified a hidden stellar-mass black hole or neutron star pulling material from a massive star named AT 2016blu every 113 days, Newswise reported.
The volatile star sits in the spiral galaxy NGC 4559, roughly 30 million light-years from Earth. Researchers estimate the mass of AT 2016blu is at least 33 times that of the Sun.
For 15 years, astronomers watched this star brighten and dim on a regular schedule. Mojgan Aghakhanloo of the University of Virginia led the study published in The Astrophysical Journal, stating that researchers needed Chandra data captured at the right time to figure out the cause.
Supernova Impostor Behavior
AT 2016blu is classified as a luminous blue variable, a hot and massive star type prone to large brightness shifts. Eta Carinae is another well-known example of this stellar category.
The extreme spikes in brightness on AT 2016blu resemble supernova explosions where a massive star collapses. However, the star survives these events, leading astronomers to term it a supernova impostor.
Between 2012 and 2026, researchers detected at least 27 optical light bursts from AT 2016blu roughly every 113 days. Co-author Núria Torres-Albà noted the initial confusion surrounding the star’s repeated survival of these eruptions.
Chandra X-Ray Data Capture
To understand the outbursts, researchers realized they required X-ray data timed precisely to coincide with an active eruption phase. Nathan Smith of the University of Arizona explained that dense gas surrounding the system gets heated by X-rays and then glows in optical wavelengths.
Chandra was selected because it is the only X-ray telescope with vision sharp enough to isolate AT 2016blu from a nearby bright X-ray source. Data gathered in March 2026 showed the star was at least 100 times brighter in X-rays than archival baseline data recorded between 2001 and 2002.
The system’s oval-shaped orbit brings the massive star and its dense companion close together. Material ejected by the star falls onto the neutron star or black hole during this closest approach.
Ultra-Luminous X-Ray Sources
The captured material orbits at high speeds close to the speed of light, heating up enough to shine brightly in X-rays. AT 2016blu is bright enough to qualify as an ultra-luminous X-ray source candidate.
Optical data collection relied on the Katzman Automatic Imaging Telescope, the Las Cumbres Observatory Global Supernova Project, and observations from the American Association of Variable Star Observers involving over 30 amateur astronomers. NASA’s Marshall Space Flight Center manages the Chandra program, while the Smithsonian Astrophysical Observatory’s Chandra X-ray Center controls operations.
