Bringing this over from the 'other bbs.' This subject has been raised on this board before, but the recent detection of strange quarks in atomic nuclei are a good pretext for raising it again. Ye olde strange-stars-versus-neutron-stars debate.

Physicists make strange matter

by Helen Briggs

Brookhaven National Laboratory has detected 30-40 nuclei with two strange quarks each after examining the results of a 100 million collisions. Neutron stars may contain super-dense lumps composed entirely of strange quarks: strange matter.

Theoretically, at least, there may even be strange stars.

Strange Star?

'Now X.-D. Li of Nanjing University, China, and colleagues suggest that J1808 [SAX J1808.4-3658] is odder still. They have used the X-ray observations to estimate the relationship between the radius and the mass of the pulsar. And they have found that it doesn’t match any of the relationships thought to hold for neutron stars -- hinting that J1808 is instead a ‘strange star’.'

Strangelets in Heavy Ion Collisions

'In essence, even though the consequences of the existence of strange quark matter are major, e.g. neutron stars are really strange quark matter stars (or perhaps have cores thereof), there is sufficient ambiguity in the parameters, and sufficiently limited data that the basic question remains open.'

Relativistic Strongly Magnetized Plasma

'In 1984 Witten proposed that strange matter made of quarks is the ground state. If this idea is true, at least some of the compact objects known to astronomers as radio pulsars, accreting X-ray sources, X-ray and gamma-ray bursters, etc. might be strange-quark-matter stars, not neutron stars as usually assumed.'

Lawrence Award: Dr. Alcock

'Another major contribution was Dr. Alcock's theory of strange matter stars. Particle theory indicates that there exists a matter instability at very high temperature and density which can create strange matter composed of strange quarks which form kaons, lambdas, and other particles that are observed in accelerator experiments. Dr. Alcock did the definitive work on the formation and structure of stars composed of strange matter that can exist in the universe at densities and temperatures above those found in now-confirmed neutron stars. He also predicted the details of how observers could detect such stars through the character of their surfaces and the interaction of baryons with these surfaces. Observers are seeking these strange matter stars by searching for very rapidly spinning pulsars (sub-millisecond) that, if they are found, can only be stable if their interiors are composed of this strange matter.'

Spin-down of Quark-core Neutron Stars, Phase Transitions and GRBs

'We study properties of an isolated quark-core neutron star in its spin-down process. We find that the central density of the star increases with time, and more neutron matter is converted into quark matter via continuous quark-hadron phase transition. As a result, the whole star contracts while its quark core increases in size and mass.... In the extreme case, catastrophic quark-hadron phase transition or pion condensation may happen to neutron stars at a rate of about 10^-6 yr^-1 per galaxy, with an energy release of about 10^52 ergs, and may be a good explanation of gamma-ray bursts (GRBs) at cosmological distances. If so, the detection of gravitational waves (GW) as counterparts of GRBs will be less likely than previously expected.... We also discuss an extremely strong magnetic field that may be formed via the dynamo process during collapse; the effects of this field on electromagnetic and gravitational radiation; and an initial high energy neutrino burst due to the production of strange quarks.'

Quadrupole Oscillations of Strange Quark Stars

'We found that whereas the general features of the w-mode spectra of quark stars and hybrid neutron stars are very similar to those of relativistic polytropes, they differ in the higher mode frequencies for both axial and polar oscillations.'

crust of rotating strange quark stars

'During the spin-down of a magnetized strange quark star with crust, the crust matter is absorbed in the equatorial region by the strange matter core. The deconfinement of absorbed crust matter is a strongly exothermic process, which would influence the cooling curve of this compact object.'

See-through stars

'If the CFL phase of quark--gluon plasma does lurk beneath every neutron star's mantle of neutrons, each should therefore have a clear and sparkling heart. But deducing what a cold, dense gobbet of quark matter really looks like will be extremely difficult.'

Strange star accreting from low-mass companion

'In December 1995, a special X-ray transient source, GRO J1744-28 was discovered. It possesses hard X-ray bursts the properties of which differ markedly from those of other known high-energy bursts. Study of the burst energy, duration, interval and spectrum suggested that this source could be a strange star accreting matter from its low-mass companion.'

Cosmological origins of strange matter

'From the models of bulk matter it is clear that this would be strange quark matter. The large mass contained in these objects makes them a good candidate for dark matter, and in fact they have certain properties consistent with many particle physics explanations of dark matter. This comes with the important caveat that it requires some conspiracy in many QCD parameters. It also assumes that the loss of energy from the hot bubbles proceeds primarily via neutrino emission and not evaporation, which is highly suspect.'

Dark Galaxies

'The Universe could have a mysterious dark side in the form of hidden "shadow galaxies" which contain no stars.... They noticed that a galaxy called UGC 10214 has a stream of material flowing out of it, as if it is being tugged away by another galaxy. But the stream of material is apparently flowing towards nothing.'