||A subtype of dwarf ellipticals (dwarf elliptical galaxy), which are companion to the
Milky Way and other similar galaxies. The first example of such objects was discovered
by Harlow Shapley (1938) in the constellation Sculptor. 22 such galaxies are known
currently to orbit the Milky Way and at least 36 exist in the Local Group of galaxies.
Nearby galaxy clusters such as the Virgo, Fornax, Centaurus, and Coma clusters contain
hundreds to thousands of individual dSph galaxies. These galaxies have very low surface
brightnesses, as low as only 1% that of the sky background. They are also among the
smallest, least luminous galaxies known. Most of the radiation from dSph galaxies
is emitted by stars in the optical portion of the electromagnetic spectrum. The lack
of strong emission lines, infrared, or radio emission suggests that these galaxies
are generally devoid of interstellar medium. The velocities of stars within dSph galaxies
are so high that them must be disrupting. However, the bulk of mass in these galaxies
might be undetected. Dynamical models that include dark matter do adequately explain
the velocity dispersion of the stars in all dSph systems. In the most extreme cases,
only 1% of the mass of the galaxy is visible. Many of the Local Group dSph galaxies
show evidence for star formation more recent than 10 Gyr.