Axion Instability Supernovae
  New particles coupled to the Standard Model can equilibrate in stellar cores
if they are sufficiently heavy and strongly coupled. In this work, we
investigate the astrophysical consequences of such a scenario for massive stars
by incorporating new contributions to the equation of state into a state of the
art stellar structure code. We focus on axions in the "cosmological triangle",
a region of parameter space with $300{\rm\,keV} \lesssim m_a \lesssim 2$ MeV,
$g_{a\gamma\gamma}\sim 10^{-5}$ GeV$^{-1}$ that is not presently excluded by
other considerations. We find that for axion masses $m_a \sim m_e $, axion
production in the core drives a new stellar instability that results in
explosive nuclear burning that either drives a series of mass-shedding
pulsations or completely disrupts the star resulting in a new type of optical
transient -- an \textit{Axion Instability Supernova}. We predict that the upper
black hole mass gap would be located at $37{\rm M}_\odot \le M\le 107{\rm
M}_\odot$ in these theories, a large shift down from the standard prediction,
which is disfavored by the detection of the mass gap in the LIGO/Virgo/KAGRA
GWTC-2 gravitational wave catalog beginning at $46_{-6}^{+17}{\rm M}_\odot$.
Furthermore, axion-instability supernovae are more common than pair-instability
supernovae, making them excellent candidate targets for JWST. The methods
presented in this work can be used to investigate the astrophysical
consequences of any theory of new physics that contains heavy bosonic particles
of arbitrary spin. We provide the tools to facilitate such studies.
