The d⁎(2380) in Neutron Stars — A New Degree of Freedom?

Elucidating the appropriate microscopic degrees of freedom within neutron stars remains an open question which impacts nuclear physics, particle physics and astrophysics. The recent discovery of the first non-trivial dibaryon, the $d^{⁎}\left(2380\right)$, provides a new candidate for an exotic degree of freedom in the nuclear equation of state at high matter densities. In this paper a first calculation of the role of the $d^{⁎}\left(2380\right)$ in neutron stars is performed based on a relativistic mean field description of the nucleonic degrees of freedom supplemented by a free boson gas of $d^{⁎}\left(2380\right)$. The calculations indicate that the $d^{⁎}\left(2380\right)$ would appear at densities around three times normal nuclear matter saturation density and comprise around 20% of the matter in the centre of heavy stars with higher fractions possible in the higher densities of merger processes. The $d^{⁎}\left(2380\right)$ would also reduce the maximum star mass by around 15% and have significant influence on the fractional proton/neutron composition. New possibilities for neutron star cooling mechanisms arising from the $d^{⁎}\left(2380\right)$ are also predicted.