The Large Magellanic Cloud (LMC), a dwarf galaxy orbiting the Milky Way and visible to astronomers in the Southern Hemisphere.AURA/NOAO/NSF
— Dwarf galaxies contain a few billion stars, as opposed to the Milky Way that contains hundreds of billions of stars.
— Assuming clear skies, some dwarf galaxies — like M32, M110 and the Magellanic Clouds — can be spied through binoculars.
Think galaxies, think big!
That's what most people will conclude when it comes to talking about galaxies, yet within this family of Goliaths, there are the big ones and there are the tiny ones.
Among the smallest of galaxies are the so-called "dwarf galaxies" that typically provide a gravitational home for a few billion stars as opposed to several hundred billion stars — like the Milky Way or Andromeda Galaxy. This delineation is vague (at best) but there are a number of dwarf galaxies within the grasp of amateur astronomers, despite their feeble output of light.
Like most galaxies, dwarf galaxies formed out of the gentle variations in the distribution of matter in the early Universe. Studies have shown that, while the rate of galaxy formation has slowed dramatically since the boom just after the Big Bang, there are still a handful of new galaxies, including dwarfs, slowly forming. More specific to dwarf galaxy formation is the process around larger galaxies where dark matter and other "baryonic" material slowly coalesces over billions of years to form new satellite galaxies.
For the amateur astronomer, there are some great examples of dwarf galaxies that can be seen in the sky, some requiring a good pair of binoculars and a couple just the naked eye.
Northern Hemisphere observers can see two great examples of dwarf galaxies in orbit around the Andromeda Galaxy. With the catalog designations M32 (Messier 32) and M110 (Messier 110) they were both recorded by Charles Messier, the 18th Century comet hunter. Both dwarf galaxies shine at around 8th magnitude, which means a good pair of binoculars and dark skies can just about detect them.
M32 is the brighter of the two and is classed as a "dwarf elliptical galaxy," 2.65 million light-years from the Milky Way. Due to its structure — the presence of old red and yellow stars and a hint of stellar formation in its core — it is now believed it may have once been a spiral galaxy that had its outer spiral arms stripped off by the immense gravity of the mighty Andromeda Galaxy. M110, on the other hand, is a "dwarf spheroidal galaxy" meaning it's similar to M32 but has a more spherical shape but may have once also been a spiral and suffered a similar fate.
Southern Hemisphere observers have a much better view of what are arguably the best dwarf galaxies in the sky: the Magellanic Clouds. Both are classed as "irregular dwarf galaxies" and were once thought to be in orbit around the Milky Way.
Both are visible as what seems to be detached portions of the Milky Way glowing faintly to its west. The Large Magellanic Cloud is the more prominent and brightest of the two and sits on the border of the constellations Dorado and Mensa.
The aptly-named Small Magellanic Cloud is found a little farther to the west in the constellation of Tucana. Both galaxies are now thought to have once been "barred spiral galaxies" that had their shape distorted by the gravity of the Milky Way.
HOWSTUFFWORKS: The Milky Way and Other Galaxies
Further observations from the Hubble Space Telescope have showed that both galaxies are traveling too fast to be in orbit around the Milky Way and are just visitors to our galactic neighborhood and will one day, head back off into the depths of intergalactic space.
As we wait for the Discovery Channel Telescope (DCT) to return some fascinating dwarf galaxy science, see if you can spot M110, M32 and the Magellanic Clouds in the night sky!