25 research outputs found
Strangeons constitute bulk strong matter-- To test using GW170817
The fundamental strong interaction determines the nature of pulsar-like
compact stars which are essentially in the form of bulk strong matter. From an
observational point of view, it is proposed that bulk strong matter could be
composed of strangeons, i.e. quark-clusters with there-light-flavor symmetry of
quarks, and therefore pulsar-like compact objects could actually be strangeon
stars. The equation of state (EOS) of strangeon stars is described in a
Lennard-Jones model for the purpose of constraining the EOS by both the tidal
deformability of GW170817 and . It is found that the
allowed parameter space is quite large as most of the Lennard-Jones EOS models
satisfy the tidal deformability constraint by GW170817. The future GW
detections for smaller values of and mass measurement for larger
values of will help a better constraint on the strangeon star
model.Comment: Accepted by the EPJA Topical Issue "The first Neutron Star Merger
Observation - Implications for Nuclear Physics
Constraining the Equation of State of Neutron Stars through GRB X-Ray Plateaus
The unknown equation of state (EoS) of neutron stars (NSs) is puzzling
because of rich non-perturbative effects of strong interaction there. A method
to constrain the EoS by using the detected X-ray plateaus of gamma-ray bursts
(GRBs) is proposed in this paper. Observations show some GRB X-ray plateaus may
be powered by strongly magnetized millisecond NSs. The properties of these NSs
should then satisfy: (i) the spin-down luminosity of these NSs should be
brighter than the observed luminosity of the X-ray plateaus; (ii) the total
rotational energy of these NSs should be larger than the total energy of the
X-ray plateaus. Through the case study of GRB 170714A, the moment of inertia of
NSs is constrained as , where is the critical
rotational period that an NS can achieve. The constraint of the radii of NSs
according to GRB 080607 is shown in Table 1.Comment: 6 pages, 2 figute, The Astrophysical Journal, 886:87, 2019 December
1, https://doi.org/10.3847/1538-4357/ab490
Constraint on the maximum mass of neutron stars using GW170817 event
We revisit the constraint on the maximum mass of cold spherical neutron stars
coming from the observational results of GW170817. We develop a new framework
for the analysis by employing both energy and angular momentum conservation
laws as well as solid results of latest numerical-relativity simulations and of
neutron stars in equilibrium. The new analysis shows that the maximum mass of
cold spherical neutron stars can be only weakly constrained as M_{\rm max}
\alt 2.3M_\odot. Our present result illustrates that the merger remnant
neutron star at the onset of collapse to a black hole is not necessarily
rapidly rotating and shows that we have to take into account the angular
momentum conservation law to impose the constraint on the maximum mass of
neutron stars.Comment: 14 pages, 5 figures, matches the version accepted by PRD for
publicatio
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
Free Energy of Anisotropic Strangeon Stars
Can pulsar-like compact objects release further huge free energy besides the
kinematic energy of rotation? This is actually relevant to the equation of
states of cold supra-nuclear matter, which is still under hot debate. Enormous
energy is surely needed to understand various observations, such as
ray bursts, fast radio bursts and soft ray repeaters. The
elastic/gravitational-free energy of solid strangeon star is revisited, with
two approaches to calculate in general relativity. It is found that huge free
energy (> erg) could be released via starquakes, given an extremely
small anisotropy (, with / the tangential/radial pressures)