Astro-quark matter: a challenge facing astroparticle physics

Quark matter both in terrestrial experiment and in astrophysics is briefly reviewed. Astrophysical quark matter could appear in the early Universe, in compact stars, and as cosmic rays. Emphasis is put on quark star as the nature of pulsars. Possible astrophysical implications of experiment-discovered sQGP are also concisely discussed.Comment: 14 pages, 4 figures and 1 table; talk presented at CosPA2007 (International Symposium on Cosmology and Particle Astrophysics, Taipei, Nov. 13-15, 2007

Trinity of Strangeon Matter

Strangeon is proposed to be the constituent of bulk strong matter, as an analogy of nucleon for an atomic nucleus. The nature of both nucleon matter (2 quark flavors, u and d) and strangeon matter (3 flavors, u, d and s) is controlled by the strong-force, but the baryon number of the former is much smaller than that of the latter, to be separated by a critical number of $A_{\rm c}\sim 10^9$. While micro nucleon matter (i.e., nuclei) is focused by nuclear physicists, astrophysical/macro strangeon matter could be manifested in the form of compact stars (strangeon star), cosmic rays (strangeon cosmic ray), and even dark matter (strangeon dark matter). This trinity of strangeon matter is explained, that may impact dramatically on today's physics.Comment: Xiamen-CUSTIPEN whorkshop on the EoS of dense matter (3-7 January 2019

The magnetospheric activity of bare strange quark stars

In Ruderman & Sutherland (RS75) model, the normal neutron stars as pulsars bear a severe problem, namely the binding energy problem that both ions (e.g., ${}_{26}^{56}$Fe) and electrons on normal neutron star surface can be pulled out freely by the unipolar generator induced electric field so that sparking on polar cap can hardly occur. {\bf This problem could be solved within the Partially Screened Gap (PSG) model in the regime of neutron stars}. However, in this paper we extensively study this problem in a bare strange quark star (BSS) model. We find that the huge potential barrier built by the electric field in the vacuum gap above polar cap could usually prevent electrons from streaming into the magnetosphere unless the electric potential of a pulsar is sufficiently lower than that at infinite interstellar medium. Other processes, such as the diffusion and thermionic emission of electrons have also been included here. Our conclusions are as follows: both positive and negative particles on a BSS's surface would be bound strongly enough to form a vacuum gap above its polar cap as long as the BSS is not charged (or not highly negative charged), and multi-accelerators could occur in a BSS's magnetosphere. Our results would be helpful to distinguish normal neutron stars and bare quark stars through pulsar's magnetospheric activities.Comment: 6 pages, 4 figures, 3 tables; accepted for publication in MNRA

Thermal and Non-thermal radiation from pulsars: hints of physics

Thermal and non-thermal radiation from pulsars carries significant information from surface and would have profound implications on the state of dense matter in compact stars. For the non-thermal radio emission, subpulse drifting phenomena suggest the existence of Ruderman-Sutherland-like gap-sparking and strong binding of particles on pulsar polar caps. While conventional neutron star models can hardly provide such a high binding energy, the strong self-bound surface of quark-cluster stars can naturally solve this problem. As for the thermal one, the featureless X-ray spectra of pulsars may indicate a bare surface without atmosphere, and the ultrarelativistic fireball of gamma-ray bursts and supernovae would also require strong self-bound surfaces. Recent achievements in measuring pulsar mass and mass-radius relation further indicate a stiff equation of state and a self-bound surface. Therefore, we conjecture that matters inside pulsar-like compact stars could be in a quark-cluster phase. The surface of quark-cluster stars is chromatically confined and could initially be bare. Such a surface can not only explain above features, but may also promote a successful core-collapse supernova, and the hydro-cyclotron oscillation of the electron sea above the surface could be responsible for those absorption features detected in the X-ray spectrum.Comment: 4 pages, contribution to the ERPM conferences, Zielona Gora, April 201