Chandra finds black hole companion for giant star AT 2016blu

Hidden companion powers eruptions

Astronomers using NASA's Chandra X-ray Observatory discovered a previously hidden companion object triggering repeated outbursts from the giant star AT 2016blu. The companion object is likely a stellar-mass black hole or the dense remnant of a massive star known as a neutron star. This unstable star resides within the spiral galaxy NGC 4559, which stands approximately 30 million light-years away from our planet. From 2012 through 2026, researchers observed no fewer than 27 flashes of optical light occurring approximately once every 113 days.

Study details timing and mass

Mojgan Aghakhanloo of the University of Virginia led this study after fifteen years of watching the star brighten and dim regularly. The star AT 2016blu is a luminous blue variable with a mass estimated at least 33 times that of the sun. Chandra data from March 2026 revealed the object was at least 100 times brighter in X-rays than data from 2001 to 2002. Material from the star falls onto the companion during their closest approach in an oval-shaped orbit around one another.

X-ray vision solves mystery

Nathan Smith of the University of Arizona noted that dense gas surrounding the system heats up due to high-energy X-rays before glowing in optical wavelengths. Núria Torres-Albà stated the star keeps surviving these outbursts about three times a year without being destroyed like a true supernova. For the first time, scientists detected an X-ray signal from an erupting star paired with either a black hole or a neutron star.