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Exotic star
An exotic star is a hypothetical compact star composed of exotic matter (something not made of electrons, protons, neutrons, or muons), and balanced against gravitational collapse by degeneracy pressure or other quantum properties.
Types of exotic stars include
Of the various types of exotic star proposed, the most well evidenced and understood is the quark star, although its existence is not confirmed.
A quark star is a hypothesized object that results from the decomposition of neutrons into their constituent quarks under extremely intense gravitational pressure balanced by electrical repulsion and degeneracy pressure. Such a star would be smaller and more dense than a neutron star, and may survive in this new state indefinitely, if no extra mass is added. Quark stars that contain strange matter are called strange stars. Such a star, first proposed by Edward Witten, would consist of confined quarks, essentialy a giant nucleon.
Based on observations released by the Chandra X-Ray Observatory on 10 April 2002, two objects, named RX J1856.5−3754 and 3C 58, were suggested as quark star candidates. The former appeared to be much smaller and the latter much colder than expected for a neutron star, suggesting that they were composed of material denser than neutronium. However, these observations were met with skepticism by researchers who said the results were not conclusive.[who?] After further analysis, RX J1856.5−3754 was excluded from the list of quark star candidates.
An electroweak star is a hypothetical type of exotic star in which the gravitational collapse of the star is prevented by radiation pressure resulting from electroweak burning; that is, the energy released by the conversion of quarks into leptons through the electroweak force. This proposed process might occur in a volume at the star's core approximately the size of an apple, containing about two Earth masses, and reaching temperatures on the order of 1015 K (1 PK). Electroweak stars could be identified through the equal number of neutrinos emitted of all three generations, taking into account neutrino oscillation.
A preon star is a proposed type of compact star made of preons, a group of hypothetical subatomic particles. Preon stars would be expected to have huge densities, exceeding 1023 kg/m3. They may have greater densities than quark stars, and they would be heavier but smaller than white dwarfs and neutron stars.
A boson star is a hypothetical astronomical object formed out of particles called bosons. Conventional stars are formed from mostly protons and electrons, which are fermions, but also contain a large proportion of helium-4 nuclei, which are bosons, and smaller amounts of various heavier nuclei, which can be either. For this type of star to exist, there must be a stable type of boson with self-repulsive interaction; one possible candidate particle is the still-hypothetical "axion" (which is also a candidate for the not-yet-detected "non-baryonic dark matter" particles, which appear to compose roughly 25% of the mass of the Universe). It is theorized that unlike normal stars (which emit radiation due to gravitational pressure and nuclear fusion), boson stars would be transparent and invisible. The immense gravity of a compact boson star would bend light around the object, creating an empty region resembling the shadow of a black hole's event horizon. Like a black hole, a boson star would absorb ordinary matter from its surroundings, but because of the transparency, matter (which would probably heat up and emit radiation) would be visible at its center. Rotating boson star models are also possible. Unlike black holes these have quantized angular momentum, and their energy density profiles are torus-shaped, which can be understood as a result of deformation due to centrifugal forces.
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Exotic star
An exotic star is a hypothetical compact star composed of exotic matter (something not made of electrons, protons, neutrons, or muons), and balanced against gravitational collapse by degeneracy pressure or other quantum properties.
Types of exotic stars include
Of the various types of exotic star proposed, the most well evidenced and understood is the quark star, although its existence is not confirmed.
A quark star is a hypothesized object that results from the decomposition of neutrons into their constituent quarks under extremely intense gravitational pressure balanced by electrical repulsion and degeneracy pressure. Such a star would be smaller and more dense than a neutron star, and may survive in this new state indefinitely, if no extra mass is added. Quark stars that contain strange matter are called strange stars. Such a star, first proposed by Edward Witten, would consist of confined quarks, essentialy a giant nucleon.
Based on observations released by the Chandra X-Ray Observatory on 10 April 2002, two objects, named RX J1856.5−3754 and 3C 58, were suggested as quark star candidates. The former appeared to be much smaller and the latter much colder than expected for a neutron star, suggesting that they were composed of material denser than neutronium. However, these observations were met with skepticism by researchers who said the results were not conclusive.[who?] After further analysis, RX J1856.5−3754 was excluded from the list of quark star candidates.
An electroweak star is a hypothetical type of exotic star in which the gravitational collapse of the star is prevented by radiation pressure resulting from electroweak burning; that is, the energy released by the conversion of quarks into leptons through the electroweak force. This proposed process might occur in a volume at the star's core approximately the size of an apple, containing about two Earth masses, and reaching temperatures on the order of 1015 K (1 PK). Electroweak stars could be identified through the equal number of neutrinos emitted of all three generations, taking into account neutrino oscillation.
A preon star is a proposed type of compact star made of preons, a group of hypothetical subatomic particles. Preon stars would be expected to have huge densities, exceeding 1023 kg/m3. They may have greater densities than quark stars, and they would be heavier but smaller than white dwarfs and neutron stars.
A boson star is a hypothetical astronomical object formed out of particles called bosons. Conventional stars are formed from mostly protons and electrons, which are fermions, but also contain a large proportion of helium-4 nuclei, which are bosons, and smaller amounts of various heavier nuclei, which can be either. For this type of star to exist, there must be a stable type of boson with self-repulsive interaction; one possible candidate particle is the still-hypothetical "axion" (which is also a candidate for the not-yet-detected "non-baryonic dark matter" particles, which appear to compose roughly 25% of the mass of the Universe). It is theorized that unlike normal stars (which emit radiation due to gravitational pressure and nuclear fusion), boson stars would be transparent and invisible. The immense gravity of a compact boson star would bend light around the object, creating an empty region resembling the shadow of a black hole's event horizon. Like a black hole, a boson star would absorb ordinary matter from its surroundings, but because of the transparency, matter (which would probably heat up and emit radiation) would be visible at its center. Rotating boson star models are also possible. Unlike black holes these have quantized angular momentum, and their energy density profiles are torus-shaped, which can be understood as a result of deformation due to centrifugal forces.