Strange quark matter and compact stars

Abstract

Astrophysicists distinguish between three different types of compact stars. These are white dwarfs, neutron stars, and black holes. The former contain matter in one of the densest forms found in the Universe which, together with the unprecedented progress in observational astronomy, make such stars superb astrophysical laboratories for a broad range of most striking physical phenomena. These range from nuclear processes on the stellar surface to processes in electron degenerate matter at subnuclear densities to boson condensates and the existence of new states of baryonic matter-like color superconducting quark matter-at supernuclear densities. More than that, according to the strange matter hypothesis strange quark matter could be more stable than nuclear matter, in which case neutron stars should be largely composed of pure quark matter possibly enveloped in thin nuclear crusts. Another remarkable implication of the hypothesis is the possible existence of a new class of white dwarfs. This article aims at giving an overview of all these striking physical possibilities, with an emphasis on the astrophysical phenomenology of strange quark matter. Possible observational signatures associated with the theoretically proposed states of matter inside compact stars are discussed as well. They will provide most valuable information about the phase diagram of superdense nuclear matter at high baryon number density but low temperature, which is not accessible to relativistic heavy ion collision experiments.

Quark core impact on hybrid star cooling

“…For the quark matter description we use the MIT Bag Model, with first order corrections in the strong interaction coupling constant (α s ) [23][24][25][26]. In the framework of the MIT Bag Model, the quarks present at the relevant densities are the up, down and strange quarks.…”

Pulsar kicks by anisotropic neutrino emission from quark matter in strong magnetic fields

“…If strange quark matter is absolutely stable, it can form selfbound stars completely made of strange quark matter only covered by a thin hadronic or strangelet crust. The first pure quark star was calculated by Itoh (1970) followed up today by a large sample of approaches for quark matter (for an overview see Schaffner-Bielich 2007Weber 2005). Up to now, quark stars cannot be excluded by observation, because they are even compatible with pulsar masses up to two solar masses, as pointed out by Alford et al (2007).…”

Absorption features caused by oscillations of electrons on the surface of a quark star

“…In this paper, we re-investigate the physics of these absorption features. The key assumption that we make here is that these features originate from the electron seas on quarks stars rather than from neutron stars, whose surface properties are radically different from those of strange stars [8,9,12]. Of key importance is the magnetic field carried by a quark star, which critically affects the global properties (hydrodynamic surface fluctuations) of the electron sea at the surface of the star.…”

“…Strange stars are quark stars made of absolutely stable strange quark matter [3][4][5][6][7][8]. They consist of essentially equal numbers of up, down and strange quarks as well as of electrons [9][10][11].…”

“…Quark matter is bound by the strong interaction, while electrons are bound to quark matter by the electromagnetic interaction. Since the latter is long-range, some of the electrons in the surface region of a quark star reside outside of the quark matter boundary, leading to a quark matter core which is surrounded by a fairly thin (thousands of femtometer thick) sea of electrons [8,9,12]. Due to the enormous advances in X-ray astronomy, more and more so-called dead pulsars are discovered, whose thermal radiation dominates over a very weak or negligibly small magnetospheric activity.…”