Andromeda Galaxy
The Andromeda Galaxy is an unbarred spiral galaxy. At a distance of approximately 2.5 million light-years, it is the closest major galaxy to the Milky Way.
Andromeda may be the dominant galaxy in the Local group of galaxies, which consists of the Andromeda Galaxy, the Milky Way Galaxy, and the Triangulum Galaxy, and about 30 other smaller galaxies. This is debated however, as some galactic astronomers believe the Milky Way contains more dark matter and may therefore be the most massive in the grouping.
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General information
The Andromeda Galaxy is approaching the Milky Way galaxy at a speed of 100 to 140 kilometres per second. However, this does not mean it will collide with the Milky Way, since the galaxy's tangential velocity is unknown. If it is on a collision course, the impact is predicted to occur in about 3 billion years. In that case the two galaxies will merge to form a giant elliptical galaxy. Such events are frequent among the galaxies in galaxy groups.
This galaxy plays an important role in galactic studies, since it is the nearest giant spiral.
Structure
The Core
The core of the Andromeda Galaxy differs from the core of the Milky Way as it seems to be split in two distinctively separate nuclear systems located within a few light years of each other. Subsequent observations have led to speculation that indeed two nuclei exist, are moving with respect to each other, that one nucleus is slowly tidally disrupting the other, and that one nucleus may be the remnant of a smaller galaxy "eaten" by the Andromeda Galaxy. Like other galactic nuclei, the core of the Andromeda is quite a violent place, and the existence of a supermassive black hole is frequently postulated to explain its properties.
The Main Disk
The disk of the Andromeda Galaxy is in fact several times larger than how it first appears, as revealed by the presence a tenuous sprinkle of stars extending outward from the galaxy. This constitutes evidence that there is a vast, extended stellar disk that makes the galaxy more than 220,000 light-years in diameter. Ancient estimates of Andromeda's size ranged from 70,000 to 120,000 light-years across.
Satellites
- Full article: List of Andromeda's satellite galaxies
Like our Milky Way, Andromeda has satellite galaxies, consisting of 14 known dwarf galaxies. The best known and most readily observed satellite galaxies are M32 and M110. Nine of these galaxies lie along a plane that intersects the core of the Andromeda Galaxy, rather than being randomly generated; This may indicate a common origin for the satellites. See Andromeda system for a full listing of objects in Andromeda's gravitational system.
Related articles
- Mayall II - the largest globular cluster in the Local Group and part of the Andromeda Galaxy.
- NGC 206 - the brightest star cloud in the Andromeda Galaxy.
- Andromedan species - a list of known species inhabiting Andromeda.
