Insights on the peak in the speed of sound of ultradense matter

Hippert, Maurício; Fraga, Eduardo S.; Noronha, Jorge

doi:10.48550/arxiv.2105.04535

Cited by 6 publications

(6 citation statements)

References 87 publications

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“…The purpose of this paper is to test the possible functional forms of the neutron star EoS using known gravitational wave and X-ray constraints in order to understand qualitative features of the speed of sound. There is a specific focus on bumps in the speed of sound that can arise due to new hadronic degrees of freedom [72], deconfinement crossover phase transitions [75,76], quarkyonic matter [51,62,65,71,77], breaking of chiral symmetry into a gapped Fermi surface [69], certain vector interactions [70], and first-order phase transitions that produce either a continuous mass-radius sequence or mass twins. These features are of interest because they can signal deconfined quark degrees of freedom within the core of neutron stars, which are of broad interest to a number of fields, including high-energy physics.…”

Section: Executive Summarymentioning

confidence: 99%

Extreme Matter meets Extreme Gravity: Ultra-heavy neutron stars with crossovers and first-order phase transitions

Tan,

Dore,

Dexheimer

et al. 2021

Preprint

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The speed of sound of the matter within neutron stars may contain non-smooth structure related to first-order phase transitions or crossovers. Here we investigate what are the observable consequences of structure in the speed of sound, such as bumps, spikes, step functions, plateaus, and kinks. One of the main consequences is the possibility of ultra-heavy neutron stars (with masses larger than 2.5 solar masses) and mass twins in heavy (with masses larger than 2 solar masses) and ultra-heavy neutron stars. These stars pass all observational and theoretical constraints, including those imposed by recent LIGO/Virgo gravitational-wave observations and NICER X-ray observations. We thoroughly investigate other consequences of this structure in the speed of sound to develop an understanding of how non-smooth features affect astrophysical observables, such as stellar radii, tidal deformability, moment of inertia, and Love number. Our results have important implications for future gravitational wave and X-ray observations of neutron stars and their impact in nuclear astrophysics.

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Section: Executive Summarymentioning

confidence: 99%

Extreme Matter meets Extreme Gravity: Ultra-heavy neutron stars with crossovers and first-order phase transitions

Tan,

Dore,

Dexheimer

et al. 2021

Preprint

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“…Models for quarkyonic matter (see, e.g., [12]) typically show a peak at low densities similar to the one in our PDF. More recently, it was shown that such peaks naturally emerge in homogeneous matter that transitions from a phase with broken chiral symmetry to a phase with a gaped Fermi surface [58].…”

mentioning

confidence: 99%

On the Sound Speed in Neutron Stars

Altiparmak¹,

Ecker²,

Rezzolla³

2022

Preprint

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Determining the sound speed cs in compact stars is an important open question with numerous implications on the behaviour of matter at large densities and hence on gravitational-wave emission from neutron stars. To this scope, we construct more than 10 7 equations of state (EOSs) with continuous sound speed and build more than 10 8 nonrotating stellar models consistent not only with nuclear theory and perturbative QCD, but also with astronomical observations. In this way, we find that EOSs with sub-conformal sound speeds, i.e., with c 2 s < 1/3 within the stars, are possible in principle but very unlikely in practice, being only 0.03% of our sample. Hence, it is natural to expect that c 2 s > 1/3 somewhere in the stellar interior. Using our large sample, we obtain estimates at 95% credibility of neutron-star radii for representative stars with 1.4 and 2.0 solar masses, R1.4 = 12.42 +0.52 −0.99 km, R2.0 = 12.12 +1.11 −1.23 km, and for the binary tidal deformability of the GW170817 event, Λ1.186 = 485 +225 −211 . Interestingly, our lower-bounds on the radii are in very good agreement with the prediction derived from very different arguments, namely, the threshold mass. Finally, we provide simple analytic expressions to determine the minimum and maximum values of Λ as a function of the chirp mass.

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“…Such statements have been confirmed both by the model calculations [95] and statistical analysis [96]. However, we should emphasize that such kind of calculations are mostly done by assuming that the compact stars are neutron stars or hybrid stars undergoing a phase transition [97].…”

Section: Sound Velocitymentioning

confidence: 63%

Landau quantization and spin polarization of cold magnetized quark matter

Lu,

Xu,

Wen

et al. 2022

Preprint

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The magnetic field and density behaviors of various thermodynamic quantities of strange quark matter under compact star conditions are investigated in the framework of the thermodynamically self-consistent quasiparticle model. For individual species, a larger number density ni leads to a larger magnetic field strength threshold that align all particles parallel or antiparallel to the magnetic field. Accordingly, in contrast to the finite baryon density effect which reduces the spin polarization of magnetized strange quark matter, the magnetic field effect leads to an enhancement of it. We also compute the sound velocity as a function of the baryon density and find the sound velocity shows an obvious oscillation with increasing density. Except for the oscillation, similar to the zero-magnetic field case that the sound velocity grows with increasing density and approaches the conformal limit V 2 s = 1/3 at high densities from below.

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Insights on the peak in the speed of sound of ultradense matter

Cited by 6 publications

References 87 publications

Extreme Matter meets Extreme Gravity: Ultra-heavy neutron stars with crossovers and first-order phase transitions

Extreme Matter meets Extreme Gravity: Ultra-heavy neutron stars with crossovers and first-order phase transitions

On the Sound Speed in Neutron Stars

Landau quantization and spin polarization of cold magnetized quark matter

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