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The galactic halo is a region of space surrounding spiral galaxies, including our galaxy, the Milky Way. The galactic halo is believed to consist largely of stars, hot gas and dark matter. In an elliptical galaxy, there is no sharp transition between the body of the galaxy and the halo. A spiral galaxy is a type of galaxy in the Hubble sequence which is characterized by the following physical properties: Spiral Galaxy M74 presents a face-on view of its spiral arms. ...
NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 56,000 light years in diameter and approximately 60 million light years distant. ...
Note: This article contains special characters. ...
The Pleiades star cluster A star is a massive body of plasma in outer space that is currently producing or has produced energy through nuclear fusion. ...
The interstellar medium (or ISM) is a term used in astronomy to describe the rarefied gas and dust that exists between the stars (or their immediate circumstellar environment) within a galaxy. ...
This refers to the cosmological use of the term. ...
An elliptical galaxy is a type of galaxy in the Hubble sequence characterized by the following physical properties: The giant elliptical galaxy NGC 4881 (the spherical glow at upper left) lies at the edge of the Coma Cluster of Galaxies. ...
Halo stars
The bulk of the stars in a spiral galaxy are located either close to a single plane (the Galactic plane) in more or less conventional circular orbits around the center of the galaxy (the galactic core), or in a spheroidal galactic bulge around the galactic core. However, some stars inhabit a spheroidal halo surrounding the galaxy. The orbital behaviour of these stars is as yet disputed, but they may describe retrograde and/or highly inclined orbits, or not to move in regular orbits at all. Halo stars may be acquired from small galaxies which fall into and merge with the spiral galaxy—for example, the Sagittarius Dwarf Elliptical Galaxy is in the process of merging with the Milky Way and observations show that some stars in the halo of the Milky Way have been acquired from it. The galactic plane is the plane in which the majority of a flattened galaxys mass lies. ...
In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ...
A spheroid is a quadric surface in three dimensions obtained by rotating an ellipse about one of its principal axes. ...
It has been proposed below that Bulge (astronomy) be renamed and moved to galactic bulge. ...
This article is about retrograde motion. ...
Inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit and is the angular distance of the orbital plane from the plane of the reference (usually planets equator or the ecliptic), stated in degrees. ...
The Sagittarius Dwarf Elliptical Galaxy (Sag DEG) is a satellite galaxy of the Milky Way Galaxy. ...
Unlike the galactic disc, the halo seems to be free of dust, and in further contrast, stars in the galactic halo are of Population II, much older and with much lower metallicity than their Population I cousins in the galactic disc (but similar to those in the galactic bulge). The galactic halo also contains many globular clusters. Interstellar cloud is the generic name given to accumulations of gas and dust in our galaxy. ...
Stars can be grouped into two general types called Population I and Population II. The criteria for classification include space velocity, location in the galaxy, age, chemical composition, and differences in distribution on the Hertzsprung-Russell diagram. ...
In astronomy, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium. ...
A globular cluster is a spherical bundle of stars (star cluster) that orbits a galaxy as a satellite. ...
The motion of halo stars does bring them through the disc on occasion, and a number of small red dwarf stars close to the Sun are thought to belong to the galactic halo, for example Kapteyn's Star and Groombridge 1830. Due to their irregular movement around the centre of the galaxy—if they do so at all—these stars often display unusually high proper motion. This article describes the British science fiction comedy television series. ...
The Sun is the star at the center of our Solar system. ...
Kapteyns Star (also known as GJ 191, HD 33793 or CD -45 1841) is a class M0 subdwarf discovered by Jacobus Kapteyn in 1897. ...
Groombridge 1830 is a star. ...
The proper motion of a star is the motion of the position of the star in the sky (the change in direction in which we see it, as opposed to the radial velocity) after eliminating the improper motions of the stars, which affect their measured coordinates but are not real...
Halo dark matter Beyond the visible, inner portion of the galactic halo lies a much larger region, known as the dark halo, extended halo or galactic corona, which contains large amounts of dark matter. The Structure of the Galaxy The galactic corona (not to be confused with the suns corona), also called the dark matter halo, is a region of space surrounding the galactic halo of spiral galaxies, including the Milky Way Galaxy that consist mostly of dark matter. ...
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. It has been suggested that gravitation be merged into this article or section. ...
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. Being macho is overconforming to traditional male gender roles or hypermasculinity and often implies misogyny. ...
In English slang, a wimp is a pushover, or a wishy-washy person. ...
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. ...
See also In astrophysics, the questions of galaxy formation and evolution are: How, from a homogeneous universe, did we obtain the very inhomogeneous one we live in? How did galaxies form? How do galaxies change over time? The formation of galaxies is still one of the most active research areas in astrophysics...
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 Structure of the Galaxy The galactic corona (not to be confused with the suns corona), also called the dark matter halo, is a region of space surrounding the galactic halo of spiral galaxies, including the Milky Way Galaxy that consist mostly of dark matter. ...
A spiral galaxy presents a face-on view of its spiral arms. ...
References - Diemand, J. & Moore, B. & Stadel, J. (2005, January 27). Earth-mass dark-matter haloes as the first structures in the early universe. In Nature, 433, 389 – 391.
External links - http://chandra.harvard.edu/photo/2006/n5746/
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