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Register a new userTidal Deformability of Strange Quark Planets and Strange Dwarfs
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Strange quark matter, which is composed of u, d, and s quarks, could be the true ground of matter. According to this hypothesis, compact stars may actually be strange quark stars, and there may even be stable strange quark dwarfs and strange quark planets. The detection of the binary neutron star merger event GW170817 provides us new clues on the equation of state of compact stars. In this study, the tidal deformability of strange quark planets and strange quark dwarfs are calculated. It is found that the tidal deformability of strange quark objects is smaller than that of normal matter counterparts. For a typical 0.6 M$_odot$ compact star, the tidal deformability of a strange dwarf is about 1.4 times less than that of a normal white dwarf. The difference is even more significant between strange quark planets and normal matter planets. Additionally, if the strange quark planet is a bare one (i.e., not covered by a normal matter curst), the tidal deformability will be extremely small, which means bare strange quark planets will hardly be distorted by tidal forces. Our study clearly proves the effectiveness of identifying strange quark objects via searching for strange quark planets through gravitational-wave observations.
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In this work we consider strange stars formed by quark matter in the color-flavor-locked (CFL) phase of color superconductivity. The CFL phase is described by a Nambu-Jona-Lasinio model with four-fermion vector and diquark interaction channels. The effect of the color superconducting medium on the gluons are incorporated into the model by including the gluon self-energy in the thermodynamic potential. We construct parametrizations of the model by varying the vector coupling $G_V$ and comparing the results to the data on tidal deformability from the GW170817 event, the observational data on maximum masses from massive pulsars such as the MSP J0740+6620, and the mass/radius fits to NICER data for PSR J003+0451. Our results points out to windows for the $G_V$ parameter space of the model, with and without gluon effects included, that are compatible with all these astrophysical constraints, namely, $0.21<G_V/G_S<0.4$, and $0.02<G_V/G_S<0.1$, respectively. We also observe a strong correlation between the tidal deformabilites of the GW170817 event and $G_V$. Our results indicate that strange stars cannot be ruled out in collisions of compact binaries from the structural point of view.
Explosive astrophysical systems, such as supernovae or compact star binary mergers, provide conditions where strange quark matter can appear. The high degree of isospin asymmetry and temperatures of several MeV in such systems may cause a transition to the quark phase already around saturation density. Observable signals from the appearance of quark matter can be predicted and studied in astrophysical simulations. As input in such simulations, an equation of state with an integrated quark matter phase transition for a large temperature, density and proton fraction range is required. Additionally, restrictions from heavy ion data and pulsar observation must be considered. In this work we present such an approach. We implement a quark matter phase transition in a hadronic equation of state widely used for astrophysical simulations and discuss its compatibility with heavy ion collisions and pulsar data. Furthermore, we review the recently studied implications of the QCD phase transition during the early post-bounce evolution of core-collapse supernovae and introduce the effects from strong interactions to increase the maximum mass of hybrid stars. In the MIT bag model, together with the strange quark mass and the bag constant, the strong coupling constant $alpha_s$ provides a parameter to set the beginning and extension of the quark phase and with this the mass and radius of hybrid stars.
Correlations between the strange quark mass, strange quark condensate $langle bar s srangle$, and the kaon partially conserved axial current (PCAC) relation are developed. The key dimensionless and renormalization-group invariant quantities in these correlations are the ratio of the strange to non-strange quark mass $r_m=m_s/m_q$, the condensate ratio $r_c=langle bar s srangle/langle bar q qrangle$, and the kaon PCAC deviation parameter $r_p=-m_slangle bar s s+bar q qrangle/2f_K^2m_K^2$. The correlations define a self-consistent trajectory in the ${r_m,r_c,r_p}$ parameter space constraining strange quark parameters that can be used to assess the compatibility of different predictions of these parameters. Combining the constraint with Particle Data Group (PDG) values of $r_m$ results in ${r_c,r_p}$ constraint trajectories that are used to asses the self-consistency of various theoretical determinations of ${r_c,r_p}$. The most precise determinations of $r_c$ and $r_p$ are shown to be mutually consistent with the constraint trajectories and provide improved bounds on $r_p$. In general, the constraint trajectories combined with $r_c$ determinations tend to provide more accurate bounds on $r_p$ than direct determinations. The ${r_c,r_p}$ correlations provide a natural identification of a self-consistent set of strange quark mass and strange quark condensate parameters.
It is shown that strange quark matter (SQM) objects, stars, and planets, can very efficiently convert the mechanical energy into hadronic energy when they oscillate. This is because the mass density at the edge of SQM objects, $rho_0{=}4.7{times}10^{14}frac{mathrm{g}}{mathrm{cm}^3}$, is the critical density below which SQM is unstable with respect to decay into photons, hadrons, and leptons. We consider here radial oscillations of SQM objects that could be induced in stellar or planetary systems where tidal interactions are ubiquitous. Oscillations of $0.1%$ radius amplitude already result in $1,$keV per unit baryon number excitation near the surface of SQM stars. The excitation energy is converted into electromagnetic energy in a short time of 1 ms, during a few oscillations. Higher amplitude oscillations result in faster energy release that could lead to fragmentation or dissolution of SQM stars. This would have significant consequences for hypothetical SQM star binaries and planetary systems of SQM planets with regard to gravitational wave emission.
In an early work, we applied a QCD-based equation of state to the study of the stellar structure of self-bound strange stars, obtaining sequences with maximum masses larger than two solar masses and radii ranging from 8 to 12 Km. In this work, we update the previous calculations and compare them with the most recent data, including the very recent determination of the mass and radius of the massive pulsar PSR J0740+6620 performed by the NICER and XMM-Newton Collaborations. Our equation of state is similar to the MIT bag model one, but it includes repulsive interactions, which turn out to be essential to reproduce the accumulated experimental information. We find that our EOS is still compatible with all astrophysical observations but the parameter window is now narrower.
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