Island Universe (Andromeda Galaxy, M31)
For many years, philosophers and early astronomers looked into the heavens and believed that what they were seeing was the sum total of the universe… that our Galaxy defined the extent of the cosmos. Faint “fuzzies” that were observed in small aperture telescopes, we thought to be large gas clouds, or Nebulae within our own Galaxy. In 1917, astronomer Heber Curtis observed a Nova event within M31. He noticed that it was 10 times fainter than he would have expected it to be, had it taken place in our galaxy. This led him to hypothesize that M31 was not a nebulae, but an “Island Universe”, a distinct galaxy separate from our own, 500,000 light years away. It wasn’t until 1925 that Edwin Hubble discovered Cepheid variable stars within M31 (which are used to determine distances in space) and was able to confirm that M31 was indeed a galaxy some 2.5 million light years from our own! This discovery by Hubble opened our understanding and the doors to further galactic observations and the realization that our Universe is made of billions of these “Island Universes” or galaxies. Each one containing billions of stars and each galaxy moving away from each other at incredible speeds (about 71 kilometers per second per mega parsec, or 256,000 kilometers per hour for every 3 million light years of space) In other words, the further the galaxy is away from our own, the faster it is moving away from us. One exception to this rule is the relationship of our own Galaxy with Andromeda. We are actually moving towards each other at 140 kilometers per second! Before you look for another galaxy to live in, relax. It will be another 3 billion years before the galaxies collide.
The Andromeda Galaxy, along with our own Galaxy, the Milky Way, are the 2 largest Spiral Galaxies in our region of the Universe. They, along with about 30 other smaller galaxies comprise a small cluster of galaxies known as the Local Group. M31 contains about 1 trillion stars, whereas the Milky Way is estimated to contain about 200 billion. There is a slight warp observed in M31, which is believed to be caused by tidal or gravitational forces from nearby galaxies. The outer spiral arms contain many HII, or star forming Nebulae, which can be seen as small red areas in the image. The blue areas are concentrations of young hot blue stars that have had their embryonic gas coverings blown off by Supernova shock waves or interstellar winds. Dust lanes can be easily observed throughout the galaxy, winding their way toward the Galactic Nucleus. Recent observations with the WFPC camera on Hubble show stars orbiting the center of M31 at tremendous speeds… 2.2 million miles per hour!! The only thing massive enough to cause such speeds would be a black hole with a mass of about 140 million suns. It is currently believed that similar black holes lie at the center of most galaxies in the universe. The galaxy M110 can be seen above M31 (note the faint dust lanes near core), and M32, a dwarf elliptical companion galaxy, is observed on the lower right edge of Andromeda. A close up is included in order to see the core with more detail. The many stars seen surrounding M31 are in the foreground, and are part of our Milky Way Galaxy. They are like bugs on our windshield as we gaze deeper into the cosmos. Almost 10 hours of data acquisition was used for this image.
Date: September 2007
Location: Star Lodge Observatory
Telescope: Takahashi FSQ 106
Camera: SBIG STL 11000
LRGB 140:140:140:140 (Astrodon Filters)
(All images copyright © Kent V. Wood)