Chandra Finds Hidden Partner Behind a Star's Repeating Outbursts

NASA said Nov. 9, 2026, that astronomers using its Chandra X-ray Observatory found what triggers repeated outbursts from the giant star AT 2016blu in the galaxy NGC 4559, about 30 million light-years away.

According to NASA Science, a new study in The Astrophysical Journal describes a previously hidden companion that pulls material from the star every 113 days as the two orbit each other. The companion is either a stellar-mass black hole or a neutron star, the dense collapsed core of a massive star. NASA says it is the first X-ray detection of this class of erupting star. Astronomers estimate the star's mass at no less than 33 times that of the Sun, per NASA.

The detail that shows how this was done: timing. Study lead Mojgan Aghakhanloo of the University of Virginia said astronomers had watched the star brighten and fade for 15 years, and could not explain it "until we were able to get Chandra data at the right time." NASA says the team used optical monitoring, including observations from more than 30 amateur astronomers, to catch an outburst in early 2026. That triggered Chandra observations in March 2026. Those showed the star at least 100 times brighter in X-rays than in Chandra data from 2001 to 2002, before the outbursts began, NASA says.

NASA calls a black hole or neutron star capturing the star's ejected material at closest approach the best explanation. Which of the two the companion is, the release does not say.

NASA says astronomers detected at least 27 optical bursts between 2012 and 2026. The star's brightness spikes resemble supernova explosions, but it survives them, so it is called a "supernova impostor."

What comes next is not stated in the NASA release. The study is published, and the release gives no follow-up observations or dates.

Stay curious.

Find more at spacedew.com and @boggleriley on X