* Astronomy

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Quark Stars

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Strangelet dwarfs

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Quark stars

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Cold Quark Matter

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Title: Cold Quark Matter
Authors: Aleksi Kurkela, Paul Romatschke, Aleksi Vuorinen
(10 Dec 2009)

We perform an O(alpha_s²) perturbative calculation of the equation of state of cold but dense QCD matter with two massless and one massive quark flavour, finding that perturbation theory converges reasonably well for quark chemical potentials above 1 GeV. Using a running coupling constant and strange quark mass, and allowing for further non-perturbative effects, our results point to a narrow range where absolutely stable strange quark matter may exist. Absent stable strange quark matter, our findings suggest that quark matter in compact star cores becomes confined to hadrons only slightly above the density of atomic nuclei. Finally, we show that equations of state including quark matter lead to hybrid star masses up to M~2M_solar, in agreement with current observations. For strange stars, we find maximal masses of M~2.75M_solar and conclude that confirmed observations of compact stars with M>2M_solar would strongly favour the existence of stable strange quark matter.

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Quark stars

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Title: Strange stars with different quark mass scalings
Authors: Ang Li, Ren-Xin Xu, Ju-Fu Lu

We investigate the stability of strange quark matter and the properties of the corresponding strange stars, within a wide range of quark mass scaling. The calculation shows that the resulting maximum mass always lies between 1.5 solar mass and 1.8 solar mass for all the scalings chosen here. Strange star sequences with a linear scaling would support less gravitational mass, and a change (increase or decrease) of the scaling around the linear scaling would lead to a larger maximum mass. Radii invariably decrease with the mass scaling. While the larger the scaling, the faster the star might spin. In addition, the variation of the scaling would cause an order of magnitude change of the strong electric field on quark surface, which is essential to support possible crusts of strange stars against gravity and may then have some astrophysical implications.

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Title: Quark stars composed of Lennard-Jones matter
Authors: Xiaoyu Lai, Renxin Xu

Quark clustering, rather than colour super-conducting, could occur in cold quark matter because of the strongly coupling between quarks at realistic baryon densities of compact stars. Although one may still not be able to calculate this conjectured matter from first principles, the inter-cluster interaction might be analogised to the interaction between inert molecules. Cold quark matter would then crystallise in a solid state if the inter-cluster potential is deep enough to trap the clusters in the wells. We apply the Lennard-Jones potential to describe the inter-cluster potential, and derive the equations of state, which are stiffer than that derived in conventional realistic models (e.g., MIT bag model). If quark stars are composed of Lennard-Jones matter, they could have high maximum masses (>2 solar masses) as well as very low masses. These features could be tested by observations.

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Recently astronomers from the University of Calgary proposed an explanation for the two brightest supernovas ever observed, designated SN 2005ap and SN 2006gy. The proposed explanation is that they happened when an extremely dense neutron star exploded and became a hypothesized object called a "quark star." SN 2006gy occurred about 240 million light-years away, and thus 240 million years in the past; SN 2005ap was nearly 5 billion light-years away, thus 5 billion years ago. Each shone 100 times brighter than the brightest regular supernova, and regular supernovae can themselves shine hundreds of times brighter than regular suns. If quark stars exist, they may hold about twice as much mass as our sun, but in an area only a few miles across. Our sun is 109 times larger than Earth, so the quark star would hold more mass than our sun in a thimble, compared to our sun's size. The stress of such confinement may cause neutrons to break down into quarks, the building block of matter. In theory a quark star could behave like one enormous subatomic particle, calling into question all manner of theories about the nature of matter, causation and space-time.

Source

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Quark stars, exotic objects that have yet to be directly observed, are part of a new theory to explain some of the brightest stellar explosions recorded in the universe.
Super-luminous supernovae, which produce more than 100 times more light energy than normal supernovae and occur in about one out of every 1,000 supernovae explosions, have long baffled astrophysicists. The problem has been finding a source for all of that extra energy.
University of Calgary astrophysicists Denis Leahy and Rachid Ouyed think they have a possible source the explosive conversion of a neutron star into a quark star.

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