An Isolated Dwarf

Some galaxies are comparatively isolated. One such galaxy is the dwarf galaxy known as DDO 190 (DDO stands for the David Dunlap Observatory where the DDO catalog was created). DDO 190 is classified as a dwarf irregular galaxy because of its relatively small size and amorphous structure with a mix of old and new stars. The older red stars are generally found in DDO 190’s outskirts, and the younger, blue ones are mostly in the interior.

DDO 190 is about 9 million light years away. It’s a member of the loosely associated Messier 94 group of galaxies. Although within the Messier 94 group, DDO 190 is fairly isolated. The galaxy’s nearest dwarf galaxy neighbor is thought to be at least 3 million light years away from DDO 190. Many of the Milky Way’s companion galaxies, including the Large and Small Magellanic Clouds, are within 20 percent of that distance. The Andromeda Galaxy is closer to the Milky Way than DDO 190 is to its nearest neighbor.

Image Credit: NASA

An Irregular Dwarf

content/uploads/2015/04/i_zwicky_18.jpg”>I_Zwicky_18I Zwicky 18 is a dwarf irregular galaxy located about 59 million light years away. Spectroscopic observations with ground-based telescopes showed that I Zwicky 18 to be almost completely made up of hydrogen and helium, the main ingredients created in the Big Bang, and galaxies with I Zwicky 18’s youthful appearance are typically found only in the early universe. Initial observations with the Hubble Space Telescope suggested an age of 500 million years, but later Hubble observations found faint, older stars in the galaxy, suggesting its star formation started at least one billion years ago and possibly as much as ten billion years ago. It’s possible that the galaxy may have formed around the same time as most other galaxies.

Image Credit: NASA / ESA

An Irregular Dwarf Galaxy

ngc-4214This is dwarf galaxy NGC 4214 which is forming clusters of new stars from its interstellar gas and dust. The young clusters of new stars are within glowing gas clouds. The gas glows because it is excited by the strong ultraviolet light emitted from the young stars forming in the gravitational collapse of the gas. These hot stars eject stellar winds moving at thousands of km/s which blow bubbles in the gas. Near the center of the galaxy, there is a cluster of hundreds of massive blue stars, each more than 10,000 X brighter than our Sun, and a huge bubble inflated by stellar winds and radiation pressure surrounds the cluster.

Image Credit: NASA / ESA