A recurrent nova super-remnant in the Andromeda galaxy.

The accretion of hydrogen onto a white dwarf star ignites a classical nova eruption-a thermonuclear runaway in the accumulated envelope of gas, leading to luminosities up to a million times that of the Sun and a high-velocity mass ejection that produces a remnant shell (mainly consisting of insterstellar medium). Close to the upper mass limit of a white dwarf (1.4 solar masses), rapid accretion of hydrogen (about 10 solar masses per year) from a stellar companion leads to frequent eruptions on timescales of years to decades.