AT 2016blu yields first X-rays and a black hole or neutron star companion

A companion has been discovered around AT 2016blu, a luminous blue variable in NGC 4559. The companion is a stellar-mass black hole or neutron star, and the system has produced the object's first detected X-rays.

AT 2016blu is a luminous blue variable in NGC 4559, listed at 30,000,000 light-years. The object is also described as a supernova impostor and is in outburst.

A companion has been discovered around AT 2016blu. It orbits every 113 days in an oval-shaped path and draws material from AT 2016blu.

The companion is identified as a stellar-mass black hole or neutron star. Material falls onto the neutron star or black hole, and captured material is reported to move close to the speed of light.

AT 2016blu recorded its first X-ray detection and is listed as the first case with a black hole or neutron star companion. The observations suggest a link to ultra-luminous X-ray sources, and the object is a candidate ultra-luminous X-ray source.

The facts list 33 solar masses for AT 2016blu, 27 optical bursts, and optical-burst entries tied to 2012 and 2026. They also list optical bursts with a 113-day value and 3 outbursts per year.

Chandra observations are dated March 2026. Chandra is listed as the sole X-ray telescope capable of separating AT 2016blu from another bright nearby X-ray source. Mojgan Aghakhanloo of the University of Virginia is the study lead, and Núria Torres-Albà and Nathan Smith are co-authors.

The event identifies a luminous blue variable with a stellar-mass black hole or neutron star companion. It is both the first X-ray detection of AT 2016blu and the first listed case with a black hole or neutron star companion.

The candidate ultra-luminous X-ray source status and the suggested link to that class connect this system to objects that contain neutron stars or black holes. Chandra is identified as the sole X-ray telescope capable of separating AT 2016blu from a neighboring bright X-ray source.