Please forward this error screen to sharedip-232292202. Not to be confused with antimatter, dark energy, dark fluid, or dark flow. Dark matter is a type of matter which has not yet been directly observed, but is thought to form a matter and interactions pdf part of the universe.
Very strong evidence suggests its existence, and a broad scientific consensus agrees that some form of dark matter is widely present in the universe and has shaped the universe’s structure. Dark matter plays a central role in the current understanding of the universe. The primary evidence for dark matter is that calculations show that many galaxies would fly apart instead of rotating, or would not have formed or move as they do, if they did not contain a large amount of matter beyond that which can be observed. The conclusion is that the universe contains far more matter in a form that cannot be currently detected. Composition of dark matter: baryonic vs.
This section needs additional citations to secondary or tertiary sources such as review articles, monographs, or textbooks. The hypothesis of dark matter has an elaborate history. The first to suggest the existence of dark matter, using stellar velocities, was Dutch astronomer Jacobus Kapteyn in 1922. In 1933, Swiss astrophysicist Fritz Zwicky, who studied galactic clusters while working at the California Institute of Technology, made a similar inference. The first robust indications that the mass to light ratio was anything other than unity came from measurements of galaxy rotation curves.
1970s provided further strong evidence, also using galaxy rotation curves. At the same time that Rubin and Ford were exploring optical rotation curves, radio astronomers were making use of new radio telescopes to map the 21 cm line of atomic hydrogen in nearby galaxies. In standard cosmology, matter is anything whose energy density scales with the inverse cube of the scale factor, i. This artist’s impression shows the expected distribution of dark matter in the Milky Way galaxy as a blue halo of material surrounding the galaxy. Dark matter can explain the ‘flat’ appearance of the velocity curve out to a large radius. The arms of spiral galaxies rotate around the galactic centre.
The luminous mass density of a spiral galaxy decreases as one goes from the centre to the outskirts. If luminous mass were all the matter, then we can model the galaxy as a point mass in the centre and test masses orbiting around it, similar to the solar system. If Kepler’s laws are correct, then the obvious way to resolve this discrepancy is to conclude that the mass distribution in spiral galaxies is not similar to that of the Solar System. Stars in bound systems must obey the virial theorem. The theorem, together with the measured velocity distribution, can be used to measure the mass distribution in a bound system, such as elliptical galaxies or globular clusters. As with galaxy rotation curves, the obvious way to resolve the discrepancy is to postulate the existence of non-luminous matter. Strong gravitational lensing as observed by the Hubble Space Telescope in Abell 1689 indicates the presence of dark matter—enlarge the image to see the lensing arcs.
From X-rays emitted by hot gas in the clusters. Generally, these three methods are in reasonable agreement that dark matter outweighs visible matter by approximately 5 to 1. Dark matter map for a patch of sky based on gravitational lensing analysis of a Kilo-Degree survey. The more massive an object, the more lensing is observed. Strong lensing is the observed distortion of background galaxies into arcs when their light passes through such a gravitational lens. It has been observed around many distant clusters including Abell 1689. By measuring the distortion geometry, the mass of the intervening cluster can be obtained.
Weak gravitational lensing investigates minute distortions of galaxies, using statistical analyses from vast galaxy surveys. By examining the apparent shear deformation of the adjacent background galaxies, the mean distribution of dark matter can be characterized. Estimated division of total energy in the universe into matter, dark matter and dark energy based on five years of WMAP data. Although both dark matter and ordinary matter are “matter”, they do not behave in the same way. In particular, in the early universe, ordinary matter was ionized and interacted strongly with radiation via Thomson scattering.
The cosmic microwave background is very close to a perfect blackbody, but contains very small temperature anisotropies of a few parts in 100,000. A sky map of anisotropies can be decomposed into an angular power spectrum, which is observed to contain a series of “acoustic peaks” at near-equal spacing but different heights. The CMB anisotropy was first discovered by COBE in 1992, though this had too coarse resolution to detect the acoustic peaks. The observed CMB angular power spectrum provides powerful evidence in support of dark matter, as its precise structure is well fitted by the Lambda-CDM model but difficult to reproduce with any competing model such as MOND. 3D map of the large-scale distribution of dark matter, reconstructed from measurements of weak gravitational lensing with the Hubble Space Telescope.
Structure formation refers to the period after the Big Bang when density perturbations collapsed to form stars, galaxies, and clusters. Prior to structure formation, the Friedmann solutions to general relativity describe a homogeneous universe. Later, small anisotropies gradually grew and condensed the homogeneous universe into stars, galaxies and larger structures. Dark matter provides a solution to this problem because it is unaffected by radiation. Therefore, its density perturbations can grow first. The resulting gravitational potential acts as an attractive potential well for ordinary matter collapsing later, speeding up the structure formation process. Type Ia supernovae can be used as “standard candles” to measure extragalactic distances, which can in turn be used to measure how fast the universe has expanded in the past.