Astromers: status and prospects

The extreme temperatures and densities of many astrophysical environments tend to destabilize nuclear isomers by inducing transitions to higher-energy states which may then cascade to ground. However, not all environments destabilize all isomers. Nuclear isomers which retain their metastable character in pertinent astrophysical environments are known as astrophysically metastable nuclear isomers, or “astromers”. Astromers can influence nucleosynthesis, altering abundances or even creating new pathways that would otherwise be inaccessible. Astromers often release energy faster or slower relative to their associated ground state, acting as heating accelerants or batteries, respectively. In stable isotopes, they may even simply remain populated after a cataclysmic event and emit observable x- or γ -rays. The variety of behaviors of these nuclear species and the effects they can have merit careful consideration in nearly every possible astrophysical environment. Here, we provide a brief overview of astromers past and present, and we outline future work that will help to illuminate their role in the cosmos.