Luo Xin-Lian

Disk Stability of the Milky Way Near the Sun

By solving Poissons equation for logarithmic density disturbance in three-dimensional (3D) spiral galaxies, the disturbed potential can be given on the disk. Combining it with the corresponding dispersion relation, the local gravitational stability of our galaxy is discussed here. We have generalized the Toomres stability criterion to the more realistic 3D galaxy models. The generalized Toomres parameter Q near the sun is 2.08 or 2.20 for two or four armed spiral galaxy models, respectively.

Quark Stars Investigated using an Improved Quasi-Particle Model

The equation of state (EOS) of cold and dense strongly interacting matter is crucial for better research of compact stars, i.e., neutron stars and quark stars. We generalize our improved quasi-particle model from finite temperature and zero chemical potential [Phys. Lett. B 711 (2012) 65] to the case of zero temperature and finite chemical potential to obtain an EOS of our improved quasi-particle model and then apply this EOS to study the structure of a quark star. The results are consistent with the most recent astronomical observational data.

A Hybrid Spin-Down Model and its Application to the Radio Quiet X-Ray Pulsar 1E 1207.4-5209

A series of newly published papers are focusing on the formation of the absorption features discovered by Chandra and XMM-Newton from the young radio quiet x-ray pulsar 1E 1207.4-5209. We try to interpret it as cyclotron absorption lines since this possibility could not be ruled out. With new development and application of a hybrid model, i.e., the magnetic dipole spin-down model combined with the neutrino cyclotron radiation spin-down model, we can easily avoid the contradiction between the normal rotation energy loss rate and the relatively lower magnetic field, and then we obtain the possible initial spin period (~0.420 s). We suppose that the progenitor of 1E 1207.4-5209 may be a white dwarf.

A New Method to Determine the Thickness of Spiral Galaxies: Apply to M31

A new method is presented to determine the thickness of spiral galaxies. Based on the rigorous solution of the Poisson equation for logarithmic density disturbance in three-dimensional spiral galaxies, we have derived an accurate dispersion relation for the stellar and gaseous disk with a finite thickness. From this relation, a new method is put forward here for determining the thickness of galaxies. We apply this way to M31 and get the thickness of about 0.7 kpc, which is in good agreement with the previous results.

The Renormalized Equation of State and Quark Star

By means of the EOS of QCD at zero temperature and finite quark chemical potential we proposed [Phys. Rev. D 78(2008)054001] in the framework of rainbow-ladder approximation of Dyson-Schwinger approach, we investigate the structure of quark star and its property. It is found that the mass-radius relation in our model is very different from that of usual quark star models, but similar to neutron star models. The obtained mass of quark star is about 1.75M⊙ ~ 2.2M⊙. The obtained radius of quark star is 22 ~ 26 km, which is obviously larger than the results in other models. The reason for this discrepancy is analyzed.

A Possible Mechanism for the Origin of Ultrastrong Magnetic Field of Magnetars

Growing observations reveal that soft gamma-ray repeaters and anomalous x-ray pulsars are magnetars. Their magnetic fields may achieve 1014−1015 G. We explore the origin of the superstrong magnetic field by considering the magnetization of the 3P2 superfluid neutrons inside neutron stars (NSs). By solving the Tolman–Oppenheimer–Volkov equations together with the equation of state adopted by Elgaroy et al. [Phys. Rev. Lett. 77 (1996) 1428] in the calculation of the neutron pairing gap, we specifically calculate the NS internal structure, the permissible region for 3P2 superfluid neutrons inside the NS, and the total magnetic moment contributed by the orderly arranged neutron vortexes. The result shows that the induced magnetic field may cover a wide range, which is consistent with the magnetic field predicted by the standard magnetic dipole radiation for pulsar spindown.

Group Velocity of the Density Waves in Galactic Disks

This letter is emphasized on the discussion of the group velocity of disturbed galactic density waves (GDW), which is one of the two most insurmountable problems in the density waves theory. In our calculation, we find that the galactic thickness has an important effect on the GDW. The dynamic time scale of GDW in our three-dimensional model can be prominently prolonged, from 36% to 60% contrasting to that of two-dimensional galactic model. However, it is still less than the lifetime of our Galaxy, which means that it is necessary to seek some other physical mechanisms to excite and sustain the GDW.

On Three-Dimensional Spiral Galaxies

Density waves in 3D spiral galaxies are studied. In order to eliminate the forbidden region near the corotation in the grand-design galaxies, we assume that the perturbation satisfies the stable condition Q(r) > 1 over all the disk except that at the corotation. Then, a new method is put forward here to determine some basic parameters of spiral galaxies. We apply it to our Galaxy, and the results are in good agreement with the previous results.

Double Degenerate Stars

Regardless of the formation mechanism, an exotic object, Double Degenerate Star (DDS), is introduced and investigated, which is composed of baryonic matter and some unknown fermion dark matter. Different from the simple White Dwarfs (WDs), there are additional gravitational force provided by the unknown fermion component inside DDSs, which may strongly affect the structure and the stability of such kind of objects. Many possible and strange observational phenomena connecting with them are concisely discussed. Similar to the normal WD, this object can also experience thermonuclear explosion as type Ia supernova explosion when DDSs mass exceeds the maximum mass that can be supported by electron degeneracy pressure. However, since the total mass of baryonic matter can be much lower than that of WD at Chandrasekhar mass limit, the peak luminosity should be much dimmer than what we expect before, which may throw a slight shadow on the standard candle of SNIa in the research of cosmology.

Fusion Reaction of 16O+14N and Its Implication for the Production of 26Al in Explosive Oxygen Burning

We suggest that the fusion reaction 16O+14N may be a new way to produce 26Al in interstellar medium. Adopting different mixing modes, we investigate the impact on the production of 26Al in explosive oxygen burning and find that the result is extremely sensitive to mixing mechanisms. In some cases, we obtain an encouraging result, for example, the greatest final abundance of 26Al reaches 7.779×10−6, which means that the explosive oxygen burning may be a new origin of 26Al.