Beyond the visible, inner portion of the galactic halo lies a much larger region, known as the dark matter halo which contains large amounts of dark matter. // This refers to the cosmological use of the term. ...

The presence of dark matter in the halo is demonstrated by its gravitational effect on a spiral galaxy's rotation curve. Without large amounts of mass in the extended halo, the rotational velocity of the galaxy should decrease at large distance from the galactic core. However, observations of spiral galaxies, particularly radio observations of line emission from neutral atomic hydrogen (known, in astronomical parlance, as HI), show that the rotation curve of most spiral galaxies remains flat far beyond the visible matter. The absence of any visible matter to account for these observations implies the presence of unobserved (i.e. dark) matter. Asserting that this dark matter does not exist would mean that the accepted theory of gravitation (General Relativity) is wrong, something that could be possible but most scientists would require extensive amounts of compelling evidence before considering it. Gravity is a force of attraction that acts between bodies that have mass. ... The rotation curve of a galaxy; that is, the orbital velocity as a function of distance from the centre of the galaxy. ... Mass is a property of a physical object that quantifies the amount of matter it contains. ... Observational astronomy is a division of astronomy concerned with getting data, in contrast with theoretical astrophysics which is mainly concerned with finding out the visional implications of physical models. ... Microwave image of 3C353 galaxy at 8. ... A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... General relativity (GR) is the geometrical theory of gravitation published by Albert Einstein in 1915. ...

The nature of dark matter in the galactic halo of spiral galaxies is still undetermined, but the most popular theories are that the dark halo is home to vast numbers of small bodies known as MACHOs and/or weakly-interacting particles known as WIMPs. Observations of the halo of the Milky Way, in search of gravitational microlensing events, show that the number of MACHOs is not likely to be sufficient to account for the required mass. Look up Macho in Wiktionary, the free dictionary This is a disambiguation page: a list of articles associated with the same title. ... This article is about the hypothetical class of particles. ... Gravitational microlensing is an astronomical technique used to find planet-sized bodies indirectly by means of their gravitational interaction with light. ... Mass is a property of a physical object that quantifies the amount of matter it contains. ...

Milky Way dark matter halo

The dark matter halo is the single largest part of the Galaxy as it covers the space between 100,000 light-years to 300,000 light-years from the galactic center. It is also the most mysterious part of the Galaxy. It is now believed that about 70% of the Galaxy is composed of dark matter, a type of matter that does not seem to interact with the rest of the Galaxy's matter and energy in anyway except through gravity. The dark matter halo is the location of nearly all of the Galaxy's dark matter, which is more than ten times as much mass as all of the visible stars, gas, and dust in the rest of the Galaxy. The dark matter halo is likely to include around 600,000,000,000 to 3,000,000,000,000 solar masses of dark matter.^[1] Note: This article contains special characters. ... Note: This article contains special characters. ... Light Years is also the American name of the Rene Laloux animated film Gandahar. ... The Galactic Center is the rotational center of the Milky Way galaxy. ... // This refers to the cosmological use of the term. ... Gravity is a force of attraction that acts between bodies that have mass. ... For alternate meanings see star (disambiguation) Hundreds of stars are visible in this image taken by the Hubble Space Telescope of the Sagittarius Star Cloud in the Milky Way Galaxy. ... Space Dust Space Dust is the dust thats floating in space. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ...

See also

• Galaxy formation and evolution
• Galactic coordinate system
• disc (galaxy)
• bulge (astronomy)
• galactic halo
• spiral arm

REDIRECT [[ --68. ... Many galaxies, including the Milky Way in which our Sun and Earth are located, are disk-shaped: the majority of their visible mass (excluding possible dark matter) lies very close to a plane. ... The most common form of galxy is the butt plug of doom A disc is a component of disc galaxies, such as spiral galaxies, or lenticular galaxies. ... It has been proposed below that Bulge (astronomy) be renamed and moved to galactic bulge. ... The galactic halo is a region of space surrounding spiral galaxies, including our galaxy, the Milky Way. ... A spiral galaxy presents a face-on view of its spiral arms. ...

External links

1. ^a  The radial velocity dispersion profile of the Galactic halo: Constraining the density profile of the dark halo of the Milky Way, Battagli et al. 2005, MNRAS, 364 (2005) 433