The Chandra X-Ray Observatory Unmasks a Supernova Impostor

The Chandra X-Ray Observatory detected an object that appeared to be a supernova but was not. The object, named AT 2016blu, is a luminous blue variable (LBV) in the spiral galaxy NGC 4559, about 30 million light years away. It exhibits periodic outbursts every 113 days, which is unlike typical supernovae. The outbursts are powered by an accretion disk around a companion object, likely a neutron star or black hole. The detection was made possible by Chandra's high angular resolution, which allowed astronomers to distinguish AT 2016blu from a nearby ultraluminous X-ray source (ULX). The outbursts are most likely triggered by periastron encounters in an eccentric binary system. The first X-ray detection of the outbursts was made in 2001-2002, but the first documented outburst was in 2016. The researchers observed 27 outbursts of optical light from the object between 2012 and 2026, with each outburst occurring approximately every 113 days. The object is 100 times brighter in X-rays than in its earlier observations. The study suggests that the outbursts are not true supernovae but are instead powered by the accretion of material from a compact companion. The object is the first known LBV system with a compact companion.

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