astrophysics - Upper Mass Limit of Quark Stars

While there is no confirmation that quark stars exist, is there any theoretical limit analogous to (but different from) the Tolman–Oppenheimer–Volkoff limit for neutron stars?

In other words, what is the maximum pressure for quark matter?

Answer

The upper mass limit for a quark star depends on your assumptions and ranges between 1 and 2 solar masses (cf. this paper (arXiv link) from 2001). It seems to me that the reason for the similarity to neutron stars' mass range is that it both compact objects satisfy the TOV equation,

$$\frac{dp}{dr}=-\frac{G}{r^2}\left[\rho+\frac{p}{c^2}\right]\left[M+4\pi r^2\frac{p}{c^2}\right]\left[1-\frac{2GM}{rc^2}\right]^{-1}$$ but with different equations of state.

For the quark star, according to the aforemention paper, the pressure is defined as

$$p(\mu)=\frac{N_f\mu^4}{4\pi^2}\left[1-2\frac{\alpha_s}{\pi}-\left(G+N_f\ln\frac{\alpha_s}\pi+\left(11-\frac23N_f\right)\ln\frac{\bar{\Lambda}}{\mu}\right)\frac{\alpha_s^2}{\pi^2}\right]$$ where $G\simeq10.4-0.536N_f+N_f\ln N_f$, $\alpha_s$ the strong coupling, $N_f$ the number of flavors (often taken as 3), $\mu$ the chemical potential, and $\bar{\Lambda}$ the renormalization subtraction point (my understanding of this term is minimal, but it seems to change the size of the mass-radius relation, but not the shape).