GW190814 as a massive rapidly rotating neutron star with exotic degrees of freedom

In the context of the massive secondary object recently observed in the compact-star merger GW190814, we investigate the possibility of producing massive neutron stars from a few different equation of state models that contain exotic degrees of freedom, such as hyperons and quarks. Our work shows that state-of-the-art relativistic mean-field models can generate massive stars reaching $\gtrsim 2.05{\mathrm{M}}_{\mathrm{Sun}}$, while being in good agreement with gravitational-wave events and x-ray pulsar observations, when quark vector interactions and nonstandard self-vector interactions are introduced. In particular, we present a new version of the Chiral Mean Field (CMF) model in which a different quark-deconfinement potential allows for stable stars with a pure quark core. When rapid rotation is considered, our models generate stellar masses that approach, and in some cases surpass $2.5{\mathrm{M}}_{\mathrm{Sun}}$. We find that in such cases fast rotation does not necessarily suppress exotic degrees of freedom due to changes in stellar central density, but require a larger amount of baryons than what is allowed in the nonrotating stars. This is not the case for pure quark stars, which can easily reach $2.5{\mathrm{M}}_{\mathrm{Sun}}$ and still possess approximately the same amount of baryons as stable nonrotating stars. We also briefly discuss possible origins for fast rotating stars with a large amount of baryons and their stability, showing how the event GW190814 can be associated with a star containing quarks as one of its progenitors.

Figure 1

Particle population within the CMF model with quarks as a function of baryon number density. The shaded region covers the jump in density generated by the first-order phase transition to deconfined quark matter. Quark number densities were divided by 3. The top panel shows the original parametrization with an additional $\omega \rho$ interaction. The bottom panel shows the effects of a modified $U$ potential and a finite quark vector-meson coupling. In both cases we keep ${\omega }^4={\omega }^6=0$.

Figure 2

Static mass-radius diagram for several CMF model equations of state (shown until the maximum mass only). Green curves present a first-order phase transition to deconfined quark matter. The grey lines show the results of varying the $\omega \rho$ vector-isovector self interaction coupling strength from $0\to 62$ for hadronic matter.

Figure 3

Same as the bottom panel of Fig. 1 but with different high order vector self interaction ${\omega }^4\ne 0$ (top panel) and ${\omega }^6\ne 0$ (bottom panel). The thick lines show a parametrization for quark matter that gives rise to an early deconfinement, while the thin lines show a parametrization for quark matter that gives rise to a late deconfinement to quark matter.

Figure 4

Mass-central density diagram for rotating stars reproduced by the CMF model allowing for a late deconfinement to quark matter. The rotational frequency increases vertically and the (almost) horizontal lines denote constant baryon number and are spaced $0.1{\mathrm{M}}_{\mathrm{Sun}}$ apart. The top panel shows results for the ${\omega }^4\ne 0$ and the bottom panel for the ${\omega }^6\ne 0$ case. The onset of hyperons and quarks is denoted by labeled vertical black lines. The color code shows angular momentum in units of $M^2$. The black dotted lines show the turning-point criterion for stability.

Figure 5

Particle population within the MBF-vBag model combination (top panel) and particle population within the vBag model, both as a function of baryon number density. Quark number densities were divided by 3.

Figure 6

Static mass-radius diagram for different equation of state models (shown until the maximum mass only).

Figure 7

Mass-central density diagram for rotating stars reproduced by different equation of state models: the MBF$+$vBag combination in the top panel and the vBag in the bottom one. Labels are the same as Fig. 4.