Why a Giant Star Keeps Faking Its Death, According to X-rays

A massive star in a distant galaxy appears to be goaded into repeated eruptions by a smaller, unseen companion, according to X-ray observations from NASA's Chandra space telescope ^[2].

The star is called AT 2016blu. It sits in the galaxy NGC 4559, about 30 million light-years from Earth, and has a mass of at least 33 times the Sun's ^[2]. For more than a decade it has flared on a schedule, and the schedule is what gave the game away.

A star that keeps pretending to die

AT 2016blu is a luminous blue variable, a hot, massive star whose brightness swings ^[2]. Its eruptions look like supernova explosions, but the star survives them. Astronomers call such objects supernova impostors ^[2].

Between 2012 and 2026 astronomers recorded at least 27 bursts of visible light from the star, recurring roughly every 113 days ^[1][2]. A star in its death throes does not keep time like that. Something was winding the clock.

The team, led by University of Virginia astronomer Mojgan Aghakhanloo, used that regularity to set a trap. They watched the star in visible light, worked out when the next outburst was due, and aimed Chandra at it for March 2026 ^[2][3].

What Chandra saw

Chandra caught the star shining strongly in X-rays. The paper reports detections across five closely spaced observations ^[1][2].

The contrast with the past is stark. In Chandra data from 2001 and 2002, taken before the star's first documented outburst, stacked observations showed no X-ray detection. In March 2026 it was at least 100 times brighter in X-rays than in those older images ^[1][2].

The paper puts the X-ray luminosity at about 10 to the power of 38.64 erg per second, with an uncertainty of 0.11 in the logarithm. It estimates that the star is losing gas onto its partner at a rate of at least 8 × 10^-8 solar masses per year ^[1].

Chandra's sharp vision mattered here. It could separate the star's X-ray signal from a nearby bright source that would blur together in a lesser instrument ^[3].

How a small star bullies a big one

The researchers' explanation is a binary interaction. The giant has a hidden companion that is either a neutron star or a stellar-mass black hole. A neutron star is the crushed core of a star that has already exploded, and a stellar-mass black hole is a collapsed star's remains, both far smaller than the giant but extremely dense ^[1][2].

The two travel on an elongated, oval-shaped orbit. When they pass at their closest, the companion's gravity captures gas from the giant. That gas moves rapidly around the compact object, heats up and emits X-rays ^[2][4].

In the team's reading, that intermittent feeding is what powers the roughly 113-day eruptions. The giant does not tantrum on its own. It is being pulled on at every close approach ^[1][2].

The paper classifies the system as a high-mass X-ray binary, a pairing of a massive star with a compact companion. It compares the system with SN 2010da, another such system whose donor star is a red supergiant ^[1].

The authors say AT 2016blu is the first known luminous blue variable supernova impostor whose eruptions are driven by intermittent accretion onto a compact object ^[1]. That is the team's own claim of a first.

What is not settled

The companion has not been identified. The observations are consistent with a compact object but cannot tell a neutron star from a black hole ^[1][2]. The study is also a preprint posted to arXiv on August 20, 2026, though its record says it has been accepted for publication in The Astrophysical Journal ^[1]. The Chandra account of the work comes from the mission's own press office ^[2].

A telescope, a network and some amateurs

The campaign leaned on a wide crowd. Optical monitoring came from the Katzman Automatic Imaging Telescope, the Las Cumbres Observatory Global Supernova Project and participants in the American Association of Variable Star Observers, including more than 30 amateur astronomers ^[2][3].

That is the quiet engine of the discovery. The X-ray detection was the headline, but it could only be timed because people with modest telescopes kept logging a faint star's brightness night after night.

Why it matters

A star like AT 2016blu is a laboratory for how massive stars shed material and change before they die. Gas lost in these episodes shapes what a star looks like in its last stages. If a companion is doing the pulling, then some stars once thought to erupt on their own may owe their outbursts to a partner ^[1][3].

The authors say the system may help researchers study other luminous blue variables and supernova impostors, and the evolution of massive stars before their deaths ^[1][3]. Whether other impostors hide companions is an open question.

The next tests are already in motion. Aghakhanloo has secured more Chandra time to observe another supernova-impostor system, and a planned 10-year survey by the Vera C. Rubin Observatory could find more such objects ^[3]. If the pattern holds, AT 2016blu will have been the first of a family.