Exotic star
Encyclopedia
An exotic star is a compact star
composed of something other than electron
s, proton
s, and neutron
s balanced against gravitational collapse
by degeneracy pressure or other quantum properties. These include quark
and strange stars (composed of quark or strange matter
) and the more speculative preon stars (composed of preons).
Exotic stars are largely theoretical, but observations released by the Chandra X-Ray Observatory
on April 10, 2002 detected two candidate quark stars, designated RX J1856.5-3754
and 3C58
, which had previously been thought to be neutron star
s. Based on the known laws of physics
, the former appeared much smaller and the latter much colder than they should, suggesting that they are composed of material denser than neutronium
. However, these observations are met with skepticism by researchers who say the results were not conclusive.
s will decompose into their component up and down quark
s when sufficient gravitational pressure is applied. In this case, the star
will shrink further and become denser, but it may survive in this new state indefinitely if no extra mass is added. It has become a very large nucleon
. A star in this hypothetical state is called a quark star. If quark stars contain strange matter
, then they are called strange stars. The pulsars RX J1856.5-3754
and 3C58
have been suggested as possible quark stars.
resulting from electroweak burning, that is, the energy released by conversion of quark
s to lepton
s through the electroweak force. This process occurs in a volume at the star's core approximately the size of an apple
, containing about two Earth masses.
The stage of life of a star that produces an electroweak star is theorized to occur after a supernova
collapse. Electroweak stars are denser than quark stars, and may form when quark degeneracy pressure is no longer able to withstand gravitational attraction, but may still be withstood by electroweak burning radiation pressure. This phase of a star's life may last upwards of 10 million years.
s, a group of hypothetical subatomic particle
s. Preon stars would be expected to have huge densities
, exceeding 1023 kilogram
per cubic meter—intermediate between quark stars and black hole
s. They may have greater densities than quark stars and neutron stars although they are smaller and lighter than white dwarfs and neutron stars. Preon stars could originate from supernova
explosions or the big bang
. Such objects could be detected in principle through gravitational lensing of gamma ray
s. Preon stars are a potential candidate for dark matter
. However, current observations from particle accelerator
s speak against the existence of preons.
In general relativity, if the star collapses to a size smaller than its Schwarzschild radius
, an event horizon
will appear at that radius and the star will become a black hole. For a one solar mass
object, the Schwarzschild radius is 3 km; so, to be consistent with general relativity, any Solar mass preon star would have to have a radius larger than this. A preon star having the same mass
as Earth
would be about the size of a tennis ball
.
that is formed out of particles called boson
s (conventional star
s are formed out of fermion
s). For this type of star to exist, there must be a stable type of boson that possesses a small mass. As of 2002 there is no significant evidence that such a star exists. However, it may become possible to detect them by the gravitational radiation emitted by a pair of co-orbiting boson stars.
Boson stars may have been formed through gravitational collapse during the primordial stages of the big bang. At least in theory, a supermassive boson star could exist at the core of a galaxy, which might explain many of the observed properties of active galactic cores
. Boson stars have also been proposed as a candidate dark matter
object.
Compact star
In astronomy, the term compact star is used to refer collectively to white dwarfs, neutron stars, other exotic dense stars, and black holes. These objects are all small for their mass...
composed of something other than electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s, proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
s, and neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
s balanced against gravitational collapse
Gravitational collapse
Gravitational collapse is the inward fall of a body due to the influence of its own gravity. In any stable body, this gravitational force is counterbalanced by the internal pressure of the body, in the opposite direction to the force of gravity...
by degeneracy pressure or other quantum properties. These include quark
Quark star
A quark star or strange star is a hypothetical type of exotic star composed of quark matter, or strange matter. These are ultra-dense phases of degenerate matter theorized to form inside particularly massive neutron stars....
and strange stars (composed of quark or strange matter
Strange matter
Strange matter is a particular form of quark matter, usually thought of as a "liquid" of up, down, and strange quarks. It is to be contrasted with nuclear matter, which is a liquid of neutrons and protons , and with non-strange quark matter, which is a quark liquid containing only up and down quarks...
) and the more speculative preon stars (composed of preons).
Exotic stars are largely theoretical, but observations released by the Chandra X-Ray Observatory
Chandra X-ray Observatory
The Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. It was named in honor of Indian-American physicist Subrahmanyan Chandrasekhar who is known for determining the maximum mass for white dwarfs. "Chandra" also means "moon" or "luminous" in Sanskrit.Chandra...
on April 10, 2002 detected two candidate quark stars, designated RX J1856.5-3754
RX J1856.5-3754
RX J1856.5-3754 is a nearby neutron star in Corona Australis. It is believed to have been created by a supernova explosion of its companion star about one million years ago and is moving 108 km/s across the sky...
and 3C58
3C58
3C58 or 3C 58 is a pulsar and surrounding synchrotron nebula within the Milky Way that is possibly associated with the supernova SN 1181. There are, however, signs that indicate that it could be several thousand years old, and thus not associated with that supernova...
, which had previously been thought to be neutron star
Neutron star
A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...
s. Based on the known laws of physics
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
, the former appeared much smaller and the latter much colder than they should, suggesting that they are composed of material denser than neutronium
Neutronium
Neutronium is a proposed name for a substance composed purely of neutrons. The word was coined by scientist Andreas von Antropoff in 1926 for the conjectured "element of atomic number zero" that he placed at the head of the periodic table...
. However, these observations are met with skepticism by researchers who say the results were not conclusive.
Quark stars and strange stars
It is possible that the neutronNeutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
s will decompose into their component up and down quark
Quark
A quark is an elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. Due to a phenomenon known as color confinement, quarks are never directly...
s when sufficient gravitational pressure is applied. In this case, the star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
will shrink further and become denser, but it may survive in this new state indefinitely if no extra mass is added. It has become a very large nucleon
Nucleon
In physics, a nucleon is a collective name for two particles: the neutron and the proton. These are the two constituents of the atomic nucleus. Until the 1960s, the nucleons were thought to be elementary particles...
. A star in this hypothetical state is called a quark star. If quark stars contain strange matter
Strange matter
Strange matter is a particular form of quark matter, usually thought of as a "liquid" of up, down, and strange quarks. It is to be contrasted with nuclear matter, which is a liquid of neutrons and protons , and with non-strange quark matter, which is a quark liquid containing only up and down quarks...
, then they are called strange stars. The pulsars RX J1856.5-3754
RX J1856.5-3754
RX J1856.5-3754 is a nearby neutron star in Corona Australis. It is believed to have been created by a supernova explosion of its companion star about one million years ago and is moving 108 km/s across the sky...
and 3C58
3C58
3C58 or 3C 58 is a pulsar and surrounding synchrotron nebula within the Milky Way that is possibly associated with the supernova SN 1181. There are, however, signs that indicate that it could be several thousand years old, and thus not associated with that supernova...
have been suggested as possible quark stars.
Electroweak stars
An electroweak star is a theoretical type of exotic star, whereby the gravitational collapse of the star is prevented by radiation pressureRadiation pressure
Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. If absorbed, the pressure is the power flux density divided by the speed of light...
resulting from electroweak burning, that is, the energy released by conversion of quark
Quark
A quark is an elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. Due to a phenomenon known as color confinement, quarks are never directly...
s to lepton
Lepton
A lepton is an elementary particle and a fundamental constituent of matter. The best known of all leptons is the electron which governs nearly all of chemistry as it is found in atoms and is directly tied to all chemical properties. Two main classes of leptons exist: charged leptons , and neutral...
s through the electroweak force. This process occurs in a volume at the star's core approximately the size of an apple
Apple
The apple is the pomaceous fruit of the apple tree, species Malus domestica in the rose family . It is one of the most widely cultivated tree fruits, and the most widely known of the many members of genus Malus that are used by humans. Apple grow on small, deciduous trees that blossom in the spring...
, containing about two Earth masses.
The stage of life of a star that produces an electroweak star is theorized to occur after a supernova
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
collapse. Electroweak stars are denser than quark stars, and may form when quark degeneracy pressure is no longer able to withstand gravitational attraction, but may still be withstood by electroweak burning radiation pressure. This phase of a star's life may last upwards of 10 million years.
Preon stars
A preon star is a proposed type of compact star made of preonPreon
In particle physics, preons are postulated "point-like" particles, conceived to be subcomponents of quarks and leptons. The word was coined by Jogesh Pati and Abdus Salam in 1974...
s, a group of hypothetical subatomic particle
Subatomic particle
In physics or chemistry, subatomic particles are the smaller particles composing nucleons and atoms. There are two types of subatomic particles: elementary particles, which are not made of other particles, and composite particles...
s. Preon stars would be expected to have huge densities
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
, exceeding 1023 kilogram
Kilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...
per cubic meter—intermediate between quark stars and black hole
Black hole
A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...
s. They may have greater densities than quark stars and neutron stars although they are smaller and lighter than white dwarfs and neutron stars. Preon stars could originate from supernova
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
explosions or the big bang
Big Bang
The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...
. Such objects could be detected in principle through gravitational lensing of gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
s. Preon stars are a potential candidate for dark matter
Dark matter
In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...
. However, current observations from particle accelerator
Particle accelerator
A particle accelerator is a device that uses electromagnetic fields to propel charged particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator. There are two basic types: electrostatic and oscillating field accelerators.In...
s speak against the existence of preons.
In general relativity, if the star collapses to a size smaller than its Schwarzschild radius
Schwarzschild radius
The Schwarzschild radius is the distance from the center of an object such that, if all the mass of the object were compressed within that sphere, the escape speed from the surface would equal the speed of light...
, an event horizon
Event horizon
In general relativity, an event horizon is a boundary in spacetime beyond which events cannot affect an outside observer. In layman's terms it is defined as "the point of no return" i.e. the point at which the gravitational pull becomes so great as to make escape impossible. The most common case...
will appear at that radius and the star will become a black hole. For a one solar mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
object, the Schwarzschild radius is 3 km; so, to be consistent with general relativity, any Solar mass preon star would have to have a radius larger than this. A preon star having the same mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
as Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
would be about the size of a tennis ball
Tennis ball
A tennis ball is a ball designed for the sport of tennis,approximately 6.7 cm in diameter. Tennis balls are generally bright green, but in recreational play can be virtually any color. Tennis balls are covered in a fibrous fluffy felt which modifies their aerodynamic properties...
.
Boson stars
A boson star is a hypothetical astronomical objectAstronomical object
Astronomical objects or celestial objects are naturally occurring physical entities, associations or structures that current science has demonstrated to exist in the observable universe. The term astronomical object is sometimes used interchangeably with astronomical body...
that is formed out of particles called boson
Boson
In particle physics, bosons are subatomic particles that obey Bose–Einstein statistics. Several bosons can occupy the same quantum state. The word boson derives from the name of Satyendra Nath Bose....
s (conventional star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s are formed out of fermion
Fermion
In particle physics, a fermion is any particle which obeys the Fermi–Dirac statistics . Fermions contrast with bosons which obey Bose–Einstein statistics....
s). For this type of star to exist, there must be a stable type of boson that possesses a small mass. As of 2002 there is no significant evidence that such a star exists. However, it may become possible to detect them by the gravitational radiation emitted by a pair of co-orbiting boson stars.
Boson stars may have been formed through gravitational collapse during the primordial stages of the big bang. At least in theory, a supermassive boson star could exist at the core of a galaxy, which might explain many of the observed properties of active galactic cores
Active galactic nucleus
An active galactic nucleus is a compact region at the centre of a galaxy that has a much higher than normal luminosity over at least some portion, and possibly all, of the electromagnetic spectrum. Such excess emission has been observed in the radio, infrared, optical, ultra-violet, X-ray and...
. Boson stars have also been proposed as a candidate dark matter
Dark matter
In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...
object.
External links
- Abstract, Are Q-stars a serious threat for stellar-mass black hole candidates?, Miller J.C., Shahbaz T., Nolan L.A, 1997
- Abstract, No observational proof of the black-hole event-horizon, Marek A. Abramowicz, Wlodek Kluzniak, Jean-Pierre Lasota, 2002
- New ScientistNew ScientistNew Scientist is a weekly non-peer-reviewed English-language international science magazine, which since 1996 has also run a website, covering recent developments in science and technology for a general audience. Founded in 1956, it is published by Reed Business Information Ltd, a subsidiary of...
issue 2643, "Could preon stars reveal a hidden reality?", 6 February 2008 - New ScientistNew ScientistNew Scientist is a weekly non-peer-reviewed English-language international science magazine, which since 1996 has also run a website, covering recent developments in science and technology for a general audience. Founded in 1956, it is published by Reed Business Information Ltd, a subsidiary of...
issue 2472, "Micro-stars may manage to avoid black-hole fate", 6 November 2008