White dwarf X-ray binary system, illustration. The white dwarf (left) is accumulating material drawn from its red giant companion star (right). Periodically, outbursts of X-ray energy occurs as this material undergoes nuclear fusion when it reaches the surface of the white dwarf, or as it emits X-rays as it spirals inwards as part of the accretion disc that has formed. Observations of a white dwarf called ASASSN-16oh suggest that the latter mechanism (the accretion disc effect) is taking place. This star is around 200,000 light years away, in the Small Magellanic Cloud in the constellation of Tucana. It is thought that this white dwarf is the fast-growing to have ever been observed. Image published in 2018.