Parametrized post-Tolman-Oppenheimer-Volkoff framework for screened modified gravity with an application to the secondary component of GW190814

The secondary component of GW190814 has mass in the range $2.5–2.67M_{\odot }$, placing it within the lower mass gap separating neutron stars from black holes. According to the predictions of general relativity and state-of-the-art nuclear equations of state, this object is too heavy to be a neutron star. In this work, we explore the possibility that this object is a neutron star under the hypothesis that general relativity is modified to include screening mechanisms and that the neutron star formed in an unscreened environment. We introduce a set of parametrized post-Tolman-Oppenheimer-Volkoff (post-TOV) equations appropriate for screened modified gravity whose free parameters are environment dependent. We find that it is possible that the GW190814 secondary could be a neutron star that formed in an unscreened environment for a range of reasonable post-TOV parameters.

Figure 1

Mass-radius relations when the post-TOV parameters are varied individually with all others fixed to their GR values. Upper: computed using the APR equations of state (EOS). Lower: computed using the SLY4 EOS. Left: the effect of varying $\gamma$. Center: the effect of varying $\beta$. Right: the effect of varying $\omega$. The parameters corresponding to each curve are given in the panels. The GR values of the post-TOV parameters are $\gamma =\beta =1$, $\omega =0$.

Figure 2

Values of $\gamma$ and $\beta$ (blue shaded region) where screened modified gravity can explain the secondary component of GW190814 as a neutron star. The panels correspond to (left) $\omega =0$ and (right) $\omega =-0.05$. Computed with (top) the APR EOS and (bottom) with the SLY4 EOS.