Quark-Cluster Stars: Hints From the Surface

Abstract

The matter inside pulsar-like compact stars could be in a quark-cluster phase since in cold dense matter at a few nuclear densities (ρ ∼ 2 − 10ρ 0 ), quarks could be coupled still very strongly and condensate in position space to form quark clusters. Quark-cluster stars are chromatically confined and could initially be bare, therefore the surface properties of quark-cluster stars would be quite different from that of conventional neutron stars. Some facts indicate that a bare and self-confined surface of pulsar-like compact stars might be necessary in order to naturally understand different observational manifestations. On one hand, as for explaining the drifting sub-pulse phenomena, the binding energy of particles on pulsar surface should be high enough to produce vacuum gaps, which indicates that pulsar's surface might be strongly self-confined. On the other hand, a bare surface of quark-cluster star can overcome the baryon contamination problem of γ-ray burst as well as promote a successful core-collapse supernova. What is more, the non-atomic thermal spectra of dead pulsars may indicate also a bare surface without atmosphere, and the hydro-cyclotron oscillation of the electron sea above the quark-cluster star surface could be responsible for those absorption features detected. These hints could reflect the property of compact star's surface and possibly the state of condensed matter inside, and then might finally result in identifying quark-cluster stars.

A corresponding-state approach to quark-cluster matter

“…We find that the maximum mass of quark-cluster stars can be well above 2M . Although, in principle, one may obtain a maximum mass high enough to explain observations in any kinds of unphysical models, we call attention to the point that the quark-cluster star model has meaningful implications for one to understand different manifestations, such as of the surface [17]. Additionally, the melting heat is also discussed, and it is shown that the solidification of newly born quark-cluster stars might explain the plateau of γ-ray bursts.…”

Compressed baryonic matter: from nuclei to pulsars

“…随着核反应实验的进展, Bethe 提出了 氢核聚变成氦核的 CNO 循环机制 [7] . 由此看来, 关 于恒星能源问题, Landau(1932) [26][27][28][29] . 过去一些相关研究归纳如下.…”

Differentiating Neutron Star Models by X-Ray Polarimetry

“…Phenomenologically, some observations may hint that a bare and self-confined surface might exist in order to naturally understand different observational manifestations (e.g., sub-pulse drifting, a non-atomic spectrum, and clean fireballs for supernova/𝛾-ray bursts). [2] It is expected that because of the low temperature gradient of a surface with degenerate electrons, the linear polarization of thermal x-ray emissions from quark-cluster stars will be very low, [3] however, a quantitative calculation has never been presented. In this Letter, we calculate the polarization behavior of quark-cluster stars and compare our results to the pre-existing conclusion of neutron stars [4] in order to test pulsar structure models by future advanced x-ray polarimetries.…”