Dark Matter
Recently, dwarf spheroidal galaxies have become key objects for the study of dark matter. The Draco Dwarf is one which has received specific attention. Radial velocity computations of Draco have revealed a large internal velocity dispersion giving a mass to luminosity ratio of up to 440 M☉/L☉, suggesting large amounts of dark matter. It has been hypothesized that large velocity dispersions could be explained as tidal dwarfs (virtually unbound stellar streams from dwarf galaxies tidally disrupted in the Milky Way potential). However, Draco Dwarf's narrow horizontal branch width does not support this model. This only leaves the dark matter explanation and makes Draco Dwarf the most dark matter dominated object known as of 2007. The dark matter distribution within Draco Dwarf is at least nearly isothermal.
At large radii, radial velocity dispersion exhibit strange behavior. One possible explanation for this would be the presence of more than one stellar population. This suggests the need for further study of Draco Dwarf population's metallicity and ages and of dwarf spheroidals in general.
Read more about this topic: Draco Dwarf
Famous quotes containing the words dark and/or matter:
“A shadow
not of a bird, not of a cloud,
draws a dark stroke over
the hills, the mind.
And another, another.
Our fears keep pace with us.”
—Denise Levertov (b. 1923)
“I am often mad, but I would hate to be nothing but mad: and I think I would lose what little value I may have as a writer if I were to refuse, as a matter of principle, to accept the warming rays of the sun, and to report them, whenever, and if ever, they happen to strike me.”
—E.B. (Elwyn Brooks)