Free Astronomy Magazine May-June 2025

37 MAY-JUNE 2025 ASTRO PUBLISHING for these novae can vary from as lit- tle as one year to many decades. Less than a dozen recurrent novae have been observed within our Milky Way Galaxy, while far more are extragalactic, meaning located outside of the Milky Way. Studying extragalactic novae helps build as- tronomers’ understanding of how different environments affect nova eruptions. The first recurrent extragalactic nova to be observed was LMC 1968- 12a (LMC68), located in the Large Magellanic Cloud — a satellite galaxy of the Milky Way. This nova has a recurrent timescale of about four years — the third-shortest of any nova — and consists of a white dwarf and a companion red sub- giant (a star much larger than the Sun). It was discovered in 1968 and its eruptions have been observed fairly regularly since 1990. T his artist’s illustration depicts an extragalactic nova eruption. Nova explosions occur in binary star systems in which a white dwarf — the dense remnant of a dead star — continually siphons stellar material from a nearby companion star. As the outer atmosphere of the companion gathers onto the surface of the white dwarf it reaches temperatures hot enough to spark an eruption. Almost all novae discovered to-date have been observed to erupt only once. But a few have been ob- served to erupt more than once, and are classified as recurrent novae. The span between eruptions for these novae can vary from as little as one year to many decades. [International Gemini Observatory/NOIRLab/NSF/AURA/M. Garlick, M. Zamani]