Observability of sharp phase transitions in neutron stars

With central densities as high as 5-10 times the nuclear saturation density, neutron stars exhibit extreme conditions that cannot be observed elsewhere. They are ideal astrophysical laboratories for probing the composition and properties of cold, ultra-dense matter. We shall discuss taking into account currently available data from observation, how to reveal possible sharp phase transitions in dense neutron star cores.Comment: 8 pages, 4 figures; contribution to the AIP Proceedings of the Xiamen-CUSTIPEN Workshop on the EOS of Dense Neutron-Rich Matter in the Era of Gravitational Wave Astronomy, Jan. 3-7, 2019, Xiamen, Chin

Tidal deformability with sharp phase transitions in (binary) neutron stars

The neutron star tidal deformability is a critical parameter which determines the pre-merger gravitational-wave signal in a neutron star merger. In this article, we show how neutron star tidal deformabilities behave in the presence of one or two sharp phase transition(s). We characterize how the tidal deformability changes when the properties of these phase transitions are modified in dense matter equation of state (EoS). Sharp phase transitions lead to the smallest possible tidal deformabilities and also induce discontinuities in the relation between tidal deformability and gravitational mass. These results are qualitatively unmodified by a modest softening of the phase transition. Finally, we test two universal relations involving the tidal deformability and show that their accuracy is limited by sharp phase transitions.Comment: 20 pages, 18 figures; accepted for publication in PR

Generic conditions for stable hybrid stars

We study the mass-radius curve of hybrid stars, assuming a single first-order phase transition between nuclear and quark matter, with a sharp interface between the quark matter core and nuclear matter mantle. We use a generic parameterization of the quark matter equation of state, which has a constant, i.e. density-independent, speed of sound ("CSS"). We argue that this parameterization provides a framework for comparison and empirical testing of models of quark matter. We obtain the phase diagram of possible forms of the hybrid star mass-radius relation, where the control parameters are the transition pressure, energy density discontinuity, and the quark matter speed of sound. We find that this diagram is sensitive to the quark matter parameters but fairly insensitive to details of the nuclear matter equation of state. We calculate the maximum hybrid star mass as a function of the parameters of the quark matter EoS, and find that there are reasonable values of those parameters that give rise to hybrid stars with mass above $2\,M_\odot$.Comment: 11 pages, 8 figures. Changes to nomenclature, references adde

Phase conversion dissipation in multicomponent compact stars

We propose a mechanism for the damping of density oscillations in multicomponent compact stars. The mechanism is the periodic conversion between different phases, i.e., the movement of the interface between them, induced by pressure oscillations in the star. The damping grows nonlinearly with the amplitude of the oscillation. We study in detail the case of r-modes in a hybrid star with a sharp interface, and we find that this mechanism is powerful enough to saturate the r-mode at very low saturation amplitude, of order $10^{-10}$, and is therefore likely to be the dominant r-mode saturation mechanism in hybrid stars with a sharp interface.Comment: 17 pages, 8 figures. Typos in Eq. (15), Eqs. (64)-(65) and Eqs. (B4)-(B5) correcte

Effects of Quark Matter on the Structural and Observational Properties of Compact Stars

In the interior of a neutron star, matter is ultra-dense with its density as high as a few times the nuclear saturation density, and extremely cold compared to its chemical potential. As a result, it is the most likely place where the theoretically-predicted strange quark matter might exist. The aim of this thesis is to reveal how the strange quark matter could influence the static properties and dynamic behaviors of compact stars. This is of great importance because it allows us to draw conclusions about the phase diagram of matter at extreme density, by investigating observable properties of compact stars despite uncertainties in their detailed structures. By studying the microscopic physics of dense matter such as charge-separation phase, hadron-quark conversion and strangeness diffusion process, and applying a generic parametrization of high-density equation of states, we explore implications about mass-radius relationship, r-mode damping and spin evolution etc. of the star. In the first part of this thesis we calculate the equation of state (EoS) of the mixed phase in strangelet dwarfs, and obtain the mass-radius relation by solving Tolman-Oppenheimer-Volkoff (TOV) equation. In the second and third parts, we first study the mass-radius relation of hybrid stars with a sharp interface between nuclear and quark matter by using the generic constant speed of sound (CSS) parameterization, and obtain the phase diagram of possible forms of the mass-radius relation. We then apply the parametrization to the Field Correlator Method (FCM) model of quark matter and express observational constraints as constraints on the CSS parameters. In the fourth part, we propose a novel mechanism for the saturation of unstable oscillation modes in multi-component compact stars based on the periodic conversion between different phases, and study in detail the case of r-modes in a hybrid star with a sharp interface, giving the saturation amplitude and its range of validity to predict observational outcomes

Signatures for quark matter from multi-messenger observations

We review the prospects for detecting quark matter in neutron star cores. We survey the proposed signatures and emphasize the importance of data from neutron star mergers, which provide access to dynamical properties that operate on short timescales that are not probed by other neutron star observables.Comment: 23 pages, 4 figures; refs. added, accepted for publicatio

The Near and The Related: Positioning and Bounding Knowledge Spheres

In his keynote lecture for the inaugural event of SFU's Institute for Transpacific Cultural Research, Chua Beng Huat spoke of the difficulty of using Western benchmarks to demarcate a new area of Asian studies. A concept like transnational comes with questions already attached regarding the flow of resources or capital between nations. But which nations? From or towards the Global North or the Global South? Westwards towards the US? Or further East towards China? For Huat and the founders of the Institute, if they were to open up new areas of research and discussion, it would be necessary to create a new term, inter-Asian, as well as a new methodology, Asia as Method

Studying strong phase transitions in neutron stars with gravitational waves

The composition of neutron stars at the extreme densities reached in their cores is currently unknown. Besides nuclear matter of normal neutrons and protons, the cores of neutron stars might harbor exotic matter such as deconfined quarks. In this paper we study strong hadron-quark phase transitions in the context of gravitational wave observations of inspiraling neutron stars. We consider upcoming detections of neutron star coalescences and model the neutron star equations of state with phase transitions through the Constant-Speed-of-Sound parametrization. We use the fact that neutron star binaries with one or more hadron-quark hybrid stars can exhibit qualitatively different tidal properties than binaries with hadronic stars of the same mass, and hierarchically model the masses and tidal properties of simulated populations of binary neutron star inspiral signals. We explore the parameter space of phase transitions and discuss under which conditions future observations of binary neutron star inspirals can identify this effect and constrain its properties, in particular the threshold density at which the transition happens and the strength of the transition. We find that if the detected population of binary neutron stars contains both hadronic and hybrid stars, the onset mass and strength of a sufficiently strong phase transition can be constrained with 50–100 detections. If the detected neutron stars are exclusively hadronic or hybrid, then it is possible to place lower or upper limits on the transition density and strength