A hidden companion may trigger a giant star's eruptions every 113 days

AT 2016blu lies in galaxy NGC 4559 about 30 million light-years away. It is a luminous blue variable roughly 33 solar masses that repeatedly brightens without truly exploding. Astronomers found optical eruptions recurring about every 113 days and triggered NASA Chandra observations during a March 2026 outburst. The X-ray source was at least 100 times brighter than in non-eruption data from 2001–2002, the first X-ray detection of this class of object. The best explanation is a hidden stellar-mass black hole or neutron star stripping material near closest approach on an eccentric orbit, heating the gas until it shines in X-rays. The companion has not been directly imaged, and its mass and orbit need more cycles, so this is a strong inference rather than a final identification.