Predictions on observing hot holographic quark star with gravitational waves

TL;DR

This work investigates hot quark matter in compact stars by deriving a finite-temperature, finite-density equation of state from a holographic 2+1 flavor QCD model and constructing two-layer hybrid stars with a quark core and a hot hadronic shell. Using a five-dimensional Einstein-Maxwell-dilaton framework calibrated to lattice data near the QCD critical endpoint, it obtains $\epsilon(p)$ for the quark phase across representative $(T,\mu)$ cases and then matches to a hadronic outer layer to form stable stars. The study analyzes mass-radius relations and I-Love-Q-C universality for these hybrid configurations, finding maximum masses of $\approx 23$–$30\,M_\odot$ and a core-dominated structure, with universal relations largely preserved for connected EoS but broken for simple pure-quark models; the resulting large tidal deformability implies that such hot QS could resemble BHs in GW signals yet remain distinguishable via nonzero TLN and EM signatures. The results offer a holographic QCD pathway to BH-mimicking compact objects, suggesting that future GW and multi-messenger observations could constrain phase transition parameters and the outer-layer physics of these exotic stars.

Abstract

We extract the equation of state of hot quark matter from a holographic 2+1 flavor QCD model, which could form the core of a stable compact star. By adding a thin hadron shell, a new type of hybrid star is constructed. With the temperature serving as a parameter, the EoS varies and we obtain stable stars with mass ranging from about 5 to 30 solar masses, and the maximum compactness around 0.2. The I-Love-Q-C relations are further discussed, and compared with the neutron star cases. These compact stars are candidates for black hole mimickers, which could be observed by gravitational waves and distinguished by properties like nonzero tidal Love number and electromagnetic signals.

Figures (8)

• Figure 1: The energy-pressure data and fitting curves under five different ${T,\mu}$ conditions. The blue dots represent the numerical data, and the red lines are the fitting curves. The data near the origin have small blanks, which indicate reaching the phase transition point.
• Figure 2: Curve of free energy and temperature at $\mu=555MeV$, where the red point indicates not only a phase transition point, but also the QCD critical endpoint.
• Figure 3: Curves of free energy and temperature at $\mu/T=6$. There is a point of intersection in the curves, which corresponds to the phase transition point. This part of the multi-valued function means that the first order phase transition occurs. The red curve corresponds to the case of $\mu=605MeV$, and above this, the points have entered the phase transition region, while the blue curve $\mu=607MeV$ has not entered.
• Figure 4: The EoS, M-R relation and I-Love-Q-C relations for "simple" quark star with different models in eq.(\ref{['eos1']}-\ref{['eq:eos5']}). For reference, the black dotted line representing a polytropic NS $\epsilon=0.09p^{0.5}$ is plotted in the panels of I-Love-Q-C relations.
• Figure 5: The EoS, M-R relation and I-Love-Q-C relations of the hybrid stars consist of quark cores and neutron outer layers with $n=1$ in eq.(\ref{['phasetran']}). For reference, the black dotted line representing a polytropic NS $\epsilon=0.09p^{0.5}$ is plotted in the panels of I-Love-Q-C relations.