dwarf galaxy

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dwarf galaxy

A galaxy that is unusually faint either because of its very small size, its very low surface brightness, or both. Since galaxies exist in a continuous range of sizes from the giant ellipticals downward, the dividing line between average and dwarf is somewhat arbitrary. Since no spiral or S0 galaxies have been observed with total magnitudes below –16, this is often used as a convenient demarcation line. They contain only a few million stars and are very difficult to observe against foreground stars because they are almost completely transparent. Dwarf galaxies may make up the bulk of the cosmic population and occur in all morphologies except as spiral galaxies.

The dwarf irregulars (dI) are the most numerous of these galaxies, and contain a significant fraction of their mass as neutral hydrogen gas in a dark halo (see also LSB galaxies). Dwarf ellipticals (dE) are dominated by metal-poor halo stars, and their lack of gas or dust suggests that any star formation occurred a long time ago in these systems. In contrast, the gas-rich blue compact dwarf (BCD) galaxies are undergoing active star formation with sizes and spectra resembling giant H II regions. See also extragalactic H II region.

dwarf galaxy

[′dwȯrf ′gal·ik·sē]
(astronomy)
An elliptical galaxy with low mass and low luminosity, having at most a few tens of millions of stars.
References in periodicals archive ?
But it is a mystery why the newly found dwarf galaxies were making batches of stars at such a high rate.
Until recently, astronomers had only found a few cosmic heavyweights in dwarf galaxies, such as the one in NGC 4395, which is a few hundred thousand times the mass of the Sun.
The study reveals almost 30 dwarf galaxies orbiting the larger Andromeda Galaxy in this regular, solar system-like plane.
Dwarf galaxies are known to be far more numerous than larger galaxies.
But if they're just making their first pass, then the effects of traveling through the Milky Way's halo will only be seen in the youngest portions of the stream--the regions closest to the dwarf galaxies.
Ironically, the same radiation that sparked universal reionization appears to have squelched star-making activities in dwarf galaxies, such as those in Brown's study.
Crossing the border into Cassiopeia, we come to two easier dwarf galaxies.
Astronomers have discovered an unexpected explanation for why they can only find a small fraction of the dwarf galaxies that are supposed to swarm around the Milky Way: cosmic friction.
Several of the young, massive star clusters -- marked by arrows -- rival entire dwarf galaxies in size.
Dwarf galaxies may not look like much, but don't be fooled.
Stars in dwarf galaxies and the Milky Way apparently started out with the same chemical compositions and a similar range of masses.
Astronomers can see many examples of mergers involving massive galaxies, but mergers of two dwarf galaxies have been hard to find.