Galaxies
Artist's Conception - The Milky Way
Where are we?
We live in a somewhat remote arm of the Milky Way. This video shows you the way from our home to a vantage point outside the Local Group.
Animation (Quicktime, 3MB)
Hubble Ultra Deep Field galaxies: Credit: NASA, ESA, S. Beckwith (STScI) and the HUDF Team
Our galaxy, the Milky Way, is typical: it has hundreds of billions of stars, enough gas and dust to make billions more stars, and at least ten times as much dark matter as all the stars and gas put together. And it’s all held together by gravity.
Like more than two-thirds of the known galaxies, the Milky Way has a spiral shape. At the center of the spiral, a lot of energy and, occasionally, vivid flares. are being generated. Based on the immense gravity that would be required explain the movement of stars and the energy expelled, the astronomers conclude that the center of the Milky Way is a supermassive black hole.
Other galaxies have elliptical shapes, and a few have unusual shapes like toothpicks or rings. The Hubble Ultra Deep Field (HUDF) shows this diversity. Hubble observed a tiny patch of sky (one-tenth the diameter of the moon) for one million seconds (11.6 days) and found approximately 10,000 galaxies, of all sizes, shapes, and colors. From the ground, we see very little in this spot, which is in the constellation Fornax.
Formation
After the Big Bang, the Universe was composed of radiation and subatomic particles. What happened next is up for debate - did small particles slowly team up and gradually form stars, star clusters, and eventually galaxies? Or did the Universe first organize as immense clumps of matter that later subdivided into galaxies?
Collisions
The shapes of galaxies are influenced by their neighbors, and, often, galaxies collide. The Milky Way is itself on a collision course with our nearest neighbor, the Andromeda galaxy. Even though it is the same age as the Milky Way, Hubble observations reveal that the stars in Andromeda's halo are much younger than those in the Milky Way. From this and other evidence, astronomers infer that Andromeda has already smashed into at least one and maybe several other galaxies.
Recent Discoveries
| September 24, 2012 | Galactic Halo Around Milky Way |
| September 19, 2012 | Ultra-Distant Galaxy Amidst Cosmic 'Dark Ages' (most distant galaxy yet?) |
| September 17, 2012 | Glowing Gas and Dark Dust in a Side-on Spiral (NGC 4634) |
| September 10, 2012 | An Actively Star-forming Galaxy (NGC 7090) |
| September 6, 2012 | Odd Galaxy Couple on Space Voyage (M60) |
| August 30, 2012 | A Surprisingly Bright Superbubble (NGC 1929 in N44) |
| July 10, 2012 | Ghost Galaxies |
| June 26, 2012 | Galaxy Cluster IDCS J1426.5+3508 and Giant Arc |
| May 31, 2012 | Milky Way is Destined for Head-on Collision with Andromeda Galaxy |
| May 17, 2012 | Intergalactic Bridge Aglow with Stars (RCS2319) |
| April 24, 2012 | The Sombrero Galaxy's Split Personality |
| April 4, 2012 | Dark Heart of a Cosmic Collision (Centaurus A) |
| March 15, 2012 | Quasars Acting as Gravitational Lenses |
| February 10, 2012 | Transforming Galaxies |
| January 11, 2012 | Double Nucleus in the Andromeda Galaxy |
| January 10, 2012 | Fireworks in the Milky Way |