Strangeon Stars

Stable micro-nucleus is 2-flavored (u and d), whereas stable macro-nucleus could be 3-flavored (u, d and s) if the light flavor symmetry restores there. Nucleons are the constituent of a nucleus, while strangeons are named as the constituent of 3-flavored baryonic matter. Gravity-compressed baryonic object created after core-collapse supernova could be strangeon star if the energy scale (~0.5 GeV) cannot be high enough for quark deconfinement and if there occurs 3-flavor symmetry restoration. Strangeon stars are explained here, including their formation and manifestation/identification. Much work, coupled with effective {micro-model} of strangeon matter, is needed to take advantage of the unique opportunities advanced facilities will provide.Comment: submitted to Proceedings of QCS2017, 20-22 Feb 2017, YITP, Japa

To differentiate neutron star models by X-ray polarimetry

The nature of pulsar is still unknown because of non-perturbative effects of the fundamental strong interaction, and different models of pulsar inner structures are then suggested, either conventional neutron stars or quark stars. Additionally, a state of quark-cluster matter is conjectured for cold matter at supranuclear density, as a result pulsars could thus be quark-cluster stars. Besides understanding different manifestations, the most important issue is to find an effective way to observationally differentiate those models. X-ray polarimetry would play an important role here. In this letter, we focus on the thermal X-ray polarization of quark/quark-cluster stars. While the thermal X-ray linear polarization percentage is typically higher than ~10% in normal neutron star models, the percentage of quark/quark-cluster stars is almost zero. It could then be an effective method to identify quark/quark-cluster stars by soft X-ray polarimetry. We are therefore expecting to detect thermal X-ray polarization in the coming decades.Comment: 4 pages, 3 figures, submitte

Strangeon Matter in a Liquid Drop Model

The liquid drop model of 2-flavored ($u$ and $d$) nucleus is well known and successful, analogically, a similar drop model for 3-flavored ($u$, $d$ and $s$) nucleus is developed. A 3-flavored nucleus conjectured could be stable only if its baryon number is lager than a critical one, $A_{\rm c}$, in which strangeons are the constituent as an analogy of nucleons for nucleus. We try to model strangeon matter in a sense of phenomenological liquid drop, with two free parameters: the mass per bayron of a strangeon in vacuum, $M$, and potential deep between strangeons, $\epsilon$. It is found that, for $M\sim$ GeV and $\epsilon\sim 100$ MeV, strangeon matter could be stable and its critical number could be as low as $A_{\rm c}=300$.Comment: submitted to Proceedings of QCS2017, 20-22 Feb 2017, YITP, Japa

Two types of glitches in a solid quark star model

Glitch (sudden spinup) is a common phenomenon in pulsar observations. However, the physical mechanism of glitch is still a matter of debate because it depends on the puzzle of pulsar's inner structure, i.e., the equation of state of dense matter. Some pulsars (e.g., Vela-like) show large glitches ({\Delta}{\nu}/{\nu}~10^-6) but release negligible energy, whereas the large glitches of AXPs/SGRs (anomalous X-ray pulsars/soft gamma repeaters) are usually (but not always) accompanied with detectable energy releases manifesting as X-ray bursts or outbursts. We try to understand this aspect of glitches in a starquake model of solid quark stars. There are actually two kinds of glitches in this scenario: bulk-invariable (Type I) and bulk-variable (Type II) ones. The total stellar volume changes (and then energy releases) significantly for the latter but not for the former. Therefore, glitches accompanied with X-ray bursts (e.g., that of AXP/SGRs) could originate from Type II starquakes induced probably by accretion, while the others without evident energy release (e.g., that of Vela pulsar) would be the result of Type I starquakes due to, simply, a change of stellar ellipticity.Comment: 6 pages, 2 figures, accepted for publication in MNRA

Supernova Neutrino in a Strangeon Star Model

The neutrino burst detected during supernova SN1987A is explained in a strangeon star model, in which it is proposed that a pulsar-like compact object is composed of strangeons (strangeon: an abbreviation of "strange nucleon"). A nascent strangeon star's initial internal energy is calculated, with the inclusion of pion excitation (energy around 10^53 erg, comparable to the gravitational binding energy of a collapsed core). A liquid-solid phase transition at temperature ~ 1-2 MeV may occur only a few ten-seconds after core-collapse, and the thermal evolution of strangeon star is then modeled. It is found that the neutrino burst observed from SN 1987A could be re-produced in such a cooling model.Comment: 15 pages, 7 figures, 1 tabe