Dark Matter

Form of matter that does not emit light, absorb light, or otherwise interact with electromagnetic radiation. Its only interactions are gravitational and dark matter particles can clump under the force of gravityAttractive force between all matter - one of the four fundamental forces. Click on Term to Read More (unlike “dark energy” which is evenly distributed throughout space). The existence of dark matter has been inferred from its gravitational effects on the dynamics of luminous tracers in galaxies and galaxyConcentration of 10⁶ to 10¹² stars, dust and gas, that are gravitationally bound. Our galaxy contains ~2 × 10¹¹ stars. There are four main types of galaxies: • Elliptical
• Lenticular
• Spiral
• Irregular
Click on Term to Read More clusters and on the bending of light rays (gravitational lensing). Recent evidence indicates that dark matter contributes about 25% of the critical densityMass of an object divided by its volume. Density is a characteristic property of a substance (rock vs. ice, e.g.). Some substances (like gases) are easily compressible and have different densities depending on how much pressure is exerted upon them. The Sun is composed of compressible gases and is much Click on Term to Read More for a flat universeThat which contains and subsumes all the laws of nature, and everything subject to those laws; the sum of all that exists physically, including matter, energy, physical laws, space, and time. Also, a cosmological model of the universe., with the remainder, except ~5% ordinary matter, as dark energyForm of energy that is gravitationally repulsive, due to a negative effective pressure. Dark energy is spread almost uniformly throughout space and appears to contribute about 70% of the present energy density of the universe. Its existence was recently inferred from observations of distant Type Ia supernovae from combining CMBR Click on Term to Read More. Much of the dark matter resides in halos encompassing luminous galaxies and in clusters of galaxies where it appears to be distributed more smoothly. Evidence from Big Bang NucleosynthesisFormation of elements in the Big Bang. Calculated abundances of these isotopes (D (deuterium = 2H), 3H, 3He, 4He, 6Li, 7Li, and 7Be) and of protons (1H) and neutrons (n) vs. time are shown in the diagram. Note that the mass fraction scale is logarithmic and very little Li and Click on Term to Read More (BBN) and the cosmic microwave background radiation indicates that most dark matter is non-baryonic, that is, not composed of quarks. Particle physics theories predict the existence of exotic weakly interacting elementary particlesParticles considered basic, indivisible, building blocks of atoms and all forms of matter. These include stable leptons (electrons and neutrinos), and quarks and bosons. Also called "elementary particles." Click on Term to Read More (WIMPs), which are hypothetical candidates for non-baryonic dark matter. Dark matter plays a critical role in shaping the formation of large-scale structure. The bulk of baryons in the universe are also dark, perhaps in the form sub-stellar objects (MACHOs).