Timed Chandra pointing catches X-rays from supernova impostor AT 2016blu

The team could book the observation because they had predicted the outburst first. "We knew when the next outburst should be," Aghakhanloo said in a press release ^[15]. Astronomers at several telescopes and more than 30 amateurs contributed to tracking the cadence ^[16]. The paper, led by Mojgan Aghakhanloo of the University of Virginia ^[14], is due in The Astrophysical Journal and is posted on arXiv ^[13].

One X-ray detection on its own is thin. It becomes evidence when set against the earlier Chandra pointings, which caught the star X-ray dark ^[7]: the pair favours a source that switches on near closest approach over one that shines steadily. The phys.org account does not say where in the 113-day cycle those 2001-02 pointings fell. If they landed far from periastron, they cost a steady-source explanation very little.

Material pulled off the massive star heats up and emits X-rays ^[8]. The team measured the luminosity of the outburst, calculated the mass accretion rate needed to produce it, and reports the two together are "consistent with the presence of a compact companion" ^[9]. That falls short of identifying it. The companion stays open between a neutron star and a black hole ^[12]. The authors also classify the system as a high-mass X-ray binary ^[11].

Twenty-seven outbursts have been detected. A 113-day recurrence across roughly 14 and a half years, 2012 through June 2026, allows about 47 periastron passages, so the detected outbursts cover something near 57 percent of them ^[22]. The authors describe the outbursts as quasiperiodic ^[4]. At that sampling, a skipped cycle or an off-schedule flare would not necessarily show up in the record.

Two earlier papers, in 2023 and 2025, had already argued that a binary explained AT 2016blu and that no explosion was coming, while leaving questions open ^[17]. What the X-ray result adds is the engine, and it adds it for one system: the authors state it as the first known case of an impostor whose outbursts are driven by intermittent accretion onto a compact object ^[10]. The star itself is at least 33 solar masses, about 29 million light-years away ^[2][1]. "It's like having a front-row seat to seeing what the star is doing before it dies," Aghakhanloo said ^[19].