May 8, 2006

Two dim dwarf galaxies found around Milky Way

WASHINGTON (Reuters) - Two dim dwarf galaxies are the Milky
Way's newest-known galactic companions, astronomers studying a
vast swath of the sky reported on Monday.

This brings the total number of dwarf galaxies in the Milky
Way's cosmic neighborhood to 14. But theorists believe there
could conceivably be hundreds more.

The two newly detected dwarfs were found in the direction
of the constellations Canes Venatici (the hunting dogs) and
Bootes (the herdsman), scientists studying the Sloan Digital
Sky Survey said in a statement.

The little galaxy found in Canes Venatici is about 640,000
light-years from the Sun, a stone's throw in cosmic terms. A
light-year is about 6 trillion miles, the distance light
travels in a year. The dwarf found in Bootes is about the same
distance from the Sun.

Even though they are close, these galaxies were hard to
spot because they were so dim, a defining characteristic of
dwarf galaxies. The new galaxy in Bootes is the faintest
discovered, with a total luminosity of 100,000 Suns.

Some astronomers theorize that there should be hundreds of
clumps of so-called cold dark matter -- slow-moving subatomic
particles left over from the earliest period of the universe --
orbiting the Milky Way, which contains Earth.

Each of these clumps should be massive enough to host a
dwarf galaxy, but so far only 14 have been found.

The two newest discoveries are among 12 spheroidal dwarf
galaxies; two more are the Large Magellanic Cloud and the Small
Magellanic Cloud, a pair of irregular dwarfs.

A galaxy is considered a dwarf if it is less than 10
percent as luminous as the Milky Way, since luminosity is
mostly a matter of the total number of stars.

The Sloan Digital Sky Survey, which is managed by a global
consortium of museums, universities and other astronomical
institutions, aims to ultimately provide detailed images of
more than one-quarter of the sky for use by the scientists.