On a century of extragalactic novae and the rise of the rapid recurrent novae

TL;DR

This paper reviews a century of extragalactic nova research, highlighting the discovery of new sub-groups like faint-fast and rapid recurrent novae, and discusses future prospects in the era of advanced surveys.

Contribution

It introduces the rapid recurrent nova subgroup and provides a comprehensive review of extragalactic nova studies over the past century.

Findings

Identification of the faint-fast and rapid recurrent nova sub-groups.

Detailed analysis of the nova M31N 2008-12a.

Insights into nova populations in nearby galaxies.

Abstract

Novae are the observable outcome of a transient thermonuclear runaway on the surface of an accreting white dwarf in a close binary system. Their high peak luminosity renders them visible in galaxies out beyond the distance of the Virgo Cluster. Over the past century, surveys of extragalactic novae, particularly within the nearby Andromeda Galaxy, have yielded substantial insights regarding the properties of their populations and sub-populations. The recent decade has seen the first detailed panchromatic studies of individual extragalactic novae and the discovery of two probably related sub-groups: the 'faint-fast' and the 'rapid recurrent' novae. In this review we summarise the past 100 years of extragalactic efforts, introduce the rapid recurrent sub-group, and look in detail at the remarkable faint-fast, and rapid recurrent, nova M31N 2008-12a. We end with a brief look forward, not to the next 100 years, but the next few decades, and the study of novae in the upcoming era of wide-field and multi-messenger time-domain surveys.