Dark matter Dark matter The axion is a hypothetical exotic particle postulated by Peccei-Quinn theory to resolve the strong-CP problem in quantum chromodynamics (QCD). The naïve first principles formulation of QCD without axions predicts that some strong interactions will violate CP-symmetry. This is never observed in practice, and the axion was postulated to be a particle (specifically a pseudo-Goldstone boson) associated with a new broken symmetry of nature, whose conservation is constructed to exclude all CP-violating terms from QCD. ...more on Wikipedia about "Axion"
Baryonic dark matter is the dark matter (matter that doesn't emit light) composed of baryons, i.e. protons and neutrons. Candidates for ...more on Wikipedia about "Baryonic dark matter"
A black hole is a concentration of mass great enough that the force of gravity prevents anything from escaping it except through quantum tunnelling behaviour (known as Hawking Radiation). The gravitational field is so strong that the escape velocity near it exceeds the speed of light. This implies that nothing, not even light, can escape its gravity, hence the word "black". The term "black hole" is widespread, even though it does not refer to a hole in the usual sense, but rather a region of space from which nothing can return. ...more on Wikipedia about "Black hole"
Brown dwarfs are sub- stellar objects (~5 to 90 Jupiter masses) that do not fuse hydrogen-1 into helium and heavier elements in their cores, as do stars on the main sequence, but have fully convective surfaces and interiors, with no chemical differentiation by depth. There is some question as to whether brown dwarfs are required to have experienced fusion at some point in their history; in any event, brown dwarfs heavier than 13 Jupiter masses () do fuse deuterium. ...more on Wikipedia about "Brown dwarf"
Cold dark matter (or CDM) is a refinement of the big bang theory that contains the additional assumption that most of the matter in the Universe consists of material which cannot be observed by its electromagnetic radiation and hence is dark while at the same time the particles making up this matter are slowly moving and hence are cold. As of 2004, most cosmologists favor the cold dark matter theory as a description of how the universe went from a smooth initial state at early times (as shown by the cosmic microwave background radiation), to the lumpy distribution of galaxies and their clusters we see today — the large-scale structure of the universe. ...more on Wikipedia about "Cold dark matter"
The cuspy halo problem arises from cosmological simulations that seem to indicate cold dark matter would form cuspy distributions — that is, increasing sharply to a high value at a central point — in the most dense areas of the universe. This would imply that the center of our galaxy, for example, should exhibit a higher dark-matter density than other areas. However, it seems rather that the centers of these galaxies likely have no cusp in the dark-matter distribution at all. ...more on Wikipedia about "Cuspy halo problem"
A dark galaxy is a galaxy size object made out of dark matter. They also contain copious amounts of gas, but little or no stars. ...more on Wikipedia about "Dark galaxy (astronomy)"
In cosmology, dark matter refers to hypothetical matter particles, of unknown composition, that do not emit or reflect enough electromagnetic radiation to be detected directly, but whose presence can be inferred from gravitational effects on visible matter such as stars and galaxies. The dark matter hypothesis aims to explain several anomalous astronomical observations, such as anomalies in the rotational speed of galaxies (the galaxy rotation problem). Estimates of the amount of matter present in galaxies, based on gravitational effects, consistently suggest that there is far more matter than is directly observable. The existence of dark matter would also resolve a number of inconsistencies in the Big Bang theory, and is crucial for structure formation. ...more on Wikipedia about "Dark matter"
The dwarf galaxy problem is one that arises from numerical cosmological simulations that predict the evolution of the distribution of matter in the universe. Dark matter seems to cluster hierarchically and in ever increasing number counts for smaller and smaller sized halos. However, while there seems to be enough observed normal-sized galaxies to account for this distribution, the number of dwarf galaxies is orders of magnitude lower than expected from simulation. ...more on Wikipedia about "Dwarf galaxy problem"
An extrasolar planet (or exoplanet) is a planet which orbits a star other than the Sun, and therefore belongs to a planetary system other than our solar system. ...more on Wikipedia about "Extrasolar planet"
Hot dark matter is a form of dark matter, which consists of particles that travel with relativistic velocities. The best candidate for hot dark matter is the neutrino. Neutrinos have very small mass, and do not partake in two of the four fundamental forces, the electromagnetic interaction, and strong interaction. They do interact with the weak nuclear force, and gravity, and are extremely difficult to detect. A few projects, such as the Super-Kamiokande neutrino observatory, in Gifu, Japan are currently studying these neutrinos. ...more on Wikipedia about "Hot dark matter"
(Massive compact halo object) :For other uses of the term macho, see Macho. ...more on Wikipedia about "Massive compact halo object"
In particle physics, the neutralino is a hypothetical particle and part of the doubling of the menagerie of particles predicted by supersymmetric theories. ...more on Wikipedia about "Neutralino"
The neutrino is an elementary particle. It has half-integer spin () and is therefore a fermion. The neutrinos observed so far all have left-handed helicity (i.e., only one of the two possible spin states is realized). The masses of the neutrinos are very small compared to most other particles, although recent experiments (see Super-Kamiokande, Sudbury Neutrino Observatory and KamLAND) are widely believed to have shown them to be nonzero. As yet, no experiment has been able to directly measure neutrino mass. Since it is an electrically neutral lepton, the neutrino interacts neither by way of the strong nor the electromagnetic force, but only through the weak force and gravitation. ...more on Wikipedia about "Neutrino"
According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type. They comprise the vast majority of stars and have a diameter and mass of less than one-third that of the Sun (down to 0.08 solar masses, which are brown dwarfs) and a surface temperature of less than 3,500 K. They emit little light, sometimes as little as 1/10,000th that of the sun. Due to the slow rate at which they burn hydrogen, red dwarfs have an enormous estimated lifespan; estimates range from tens of billions up to trillions of years. Red dwarfs never initiate helium fusion and so cannot become red giants; the stars slowly contract and heat up until all the hydrogen is consumed. In any event, there has not been sufficient time since the Big Bang for red dwarfs to evolve off the main sequence. ...more on Wikipedia about "Red dwarf"
In astrophysics SIMP is an abbreviation of Strongly Interacting Massive Particle. SIMPs could form the inferred dark matter despite their strong interactions with ordinary matter [1]. ...more on Wikipedia about "SIMP"
VIRGOHI21 is a dark matter halo in the Virgo cluster. It is the size of a galaxy, but apparently contains no stars. It was detected through H-I emissions of neutral hydrogen (21 cm emissions) in the dark galaxy. This is the first discovery of the postulated dark matter clumps and galaxies anticipated by dark-matter theories. ...more on Wikipedia about "VIRGOHI21"
A white dwarf is an astronomical object which is produced when a low or medium mass star dies. These stars are not heavy enough to generate the core temperatures required to fuse carbon in nucleosynthesis reactions, and after they have become a red giant during their helium-burning phase, they will shed their outer layers to form a planetary nebula, leaving behind an inert core consisting mostly of carbon and oxygen. ...more on Wikipedia about "White dwarf"
In astrophysics, WIMPs, or weakly interacting massive particles, are hypothetical particles serving as one possible solution to the dark matter problem. These particles interact through the weak nuclear force and gravity, and possibly through other interactions no stronger than the weak force. Because they do not interact with electromagnetism they cannot be seen directly, and because they do not interact with the strong nuclear force they do not react strongly with atomic nuclei. ...more on Wikipedia about "WIMP"
This article is licensed under the GNU Free Documentation License.
It uses material from the Wikipedia . Direct links to the original articles are in the text.
If you use exact copy or modified of this article you should preserve above paragraph and put also : It uses material from
the Shortopedia article about "Dark matter".
| MAIN PAGE | MAIN INDEX | CONTACT US |