L. M. Lin

The Spin Parameter of Uniformly Rotating Compact Stars

We study the dimensionless spin parameter j(=cJ/(GM 2)) of uniformly rotating neutron stars and quark stars in general relativity. We show numerically that the maximum value of the spin parameter of a neutron star rotating at the Keplerian frequency is j max ~ 0.7 for a wide class of realistic equations of state. This upper bound is insensitive to the mass of the neutron star if the mass of the star is larger than about 1 M ☉. On the other hand, the spin parameter of a quark star modeled by the MIT bag model can be larger than unity and does not have a universal upper bound. Its value also depends strongly on the bag constant and the mass of the star. Astrophysical implications of our finding will be discussed.

Gravitational Waves from Phase-Transition-Induced Collapse of Neutron Stars

We study the gravitational wave signals emitted from phase-transition induced collapses of rapidly rotating neutron stars to strange stars by performing 3D numerical simulations.

Testing universal relations of neutron stars with a nonlinear matter-gravity coupling theory

Due to our ignorance of the equation of state (EOS) beyond nuclear density, there is still no unique theoretical model for neutron stars (NSs). It is therefore surprising that universal EOS-independent relations connecting different physical quantities of neutron stars can exist. Lau et al. [ApJ, 714, 1234 (2010)] found that the frequency of the

Compact stars in Eddington-inspired Born-Infeld gravity: Anomalies associated with phase transitions

f

Radial oscillations and stability of compact stars in Eddington inspired Born-Infeld gravity

-mode oscillation, the mass, and the moment of inertia are connected by universal relations. More recently, Yagi and Yunes [Science, 341, 365 (2013)] discovered the I-Love-Q universal relations among the mass, the moment of inertia, the Love number, and the quadrupole moment. In this paper, we study these universal relations in the Eddington-inspired Born-Infeld (EiBI) gravity. This theory differs from general relativity (GR) significantly only at high densities due to the nonlinear coupling between matter and gravity. It thus provides us an ideal case to test how robust the universal relations of NSs are with respect to the change of the gravity theory. Thanks to the apparent EOS formulation of EiBI gravity developed recently by Delsate and Steinhoff [Phys. Rev. Lett., 109, 021101 (2012)], we are able to study the universal relations in EiBI gravity using the same techniques as those in GR. We find that the universal relations in EiBI gravity are essentially the same as those in GR. Our work shows that, within the currently viable coupling constant, there exists at least one modified gravity theory that is indistinguishable from GR in view of the unexpected universal relations.

COULD THE COMPACT REMNANT OF SN 1987A BE A QUARK STAR

We study how generic phase transitions taking place in compact stars constructed in the framework of the Eddington-inspired Born-Infeld (EiBI) gravity can lead to anomalous behavior of these stars. For the case with first-order phase transitions, compact stars in EiBI gravity with a positive coupling parameter

Dark-matter admixed neutron stars

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Constraining crystalline color superconducting quark matter with gravitational-wave data

exhibit a finite region with constant pressure, which is absent in general relativity. However, for the case with a negative

Inferring Physical Parameters of Compact Stars from their f-mode Gravitational Wave Signals

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Dark-matter admixed white dwarfs

, an equilibrium stellar configuration cannot be constructed. Hence, EiBI gravity seems to impose stricter constraints on the microphysics of stellar matter. Besides, in the presence of spatial discontinuities in the sound speed