Chandra links a giant star’s repeated outbursts to a compact companion
X-rays from a repeatedly brightening massive star favour a compact companion drawing in matter. A peer-reviewed observational study places the system among binaries containing a massive star and a dense stellar remnant. The measurements support a black hole or neutron star, while the companion’s unmeasured mass leaves its identity unresolved.
Science··Morning
X-rays point to a dense companion
A dense stellar remnant provides an explanation for the repeated outbursts of a giant star. The proposed companion draws in material from the larger star, releasing energy as the matter falls toward it.[1], [2]
The system is AT 2016blu in the galaxy NGC 4559. NASA’s Chandra X-ray Observatory detected it during an optical outburst in March. The peer-reviewed observational study favours accretion, the accumulation of matter onto a compact object, over ordinary stellar-wind collisions.[1]
A surviving star keeps brightening
Observers detected 27 outbursts between 2012 and June, recurring roughly every 113 days. The star survives these events, earning the system the classification of a supernova impostor. Earlier measurements put the massive star at no less than 33 solar masses. Five Chandra observations across four days captured X-rays in every exposure, at luminosities compatible within their uncertainties.[1]
The companion’s identity remains unresolved
The detected luminosity was about 100 times the upper limit from archival observations in 2001–2002. Its power and hard spectrum favour a black hole or neutron star. Spectral lines failed to yield a reliable orbital mass, and too few X-ray photons were available to search for regular neutron-star pulsations. The short observing span also leaves open whether the brightest point was captured.[1]
