Edge of the Observable Universe
Edge of the Observable Universe
Goals: View the cosmic microwave background radiation in context with the quasars.
Before starting, turn on: galaxy, local, SloanQSOs, 20Gly
You will be using: wmap
The Cosmic Microwave Background Radiation
Astronomers believe that the Universe was born from the Big Bang, when space expanded from an extremely hot and dense condition. You might imagine that this event was spectacular in its energy and luminosity output. If we think quasars are bright, the creation of the Universe must have been incredible. Given that, wouldn't you expect to see something from this energetic event?
In fact, astronomers do see the light from the Big Bang. Just after the Big Bang, the Universe was very hot, so hot that atoms could not form. Instead, there were free electrons and protons and neutrons that made up the primordial Universe. Light could not travel very far before it collided with a free electron. Thus we say the Universe was opaque, as radiation and matter were constantly interacting. As the Universe expanded, the temperature of the plasma dropped and, after 379,000 years, the Universe was cool enough to allow electrons and protons to combine, forming hydrogen atoms. Once this occurred, the light from the Big Bang was free to traverse the Universe, since the free electrons were captured by atomic nuclei.
Bring up the Extragalactic Atlas and load the Galaxy image, local galaxies, Sloan quasars, and the 20 billion-light-year grid. Now fly away from the Milky Way but remain within the quasar data, somewhere around 15 billion light-years away.
The WMAP All-Sky Survey
From this perspective, turn on the wmap group and begin orbiting the Milky Way [see “Microwave (WMAP) All-Sky Survey” for information on the WMAP image]. The image is a false-color mapping of the tiny temperature fluctuations in the microwave light: red for the warmer regions, blue for the cooler regions. These minute differences represent temperature fluctuations in the primordial Universe. While the Universe was remarkably uniform in temperature at 379,000 years old, the seeds of structure were present. These seeds would one day grow to become the galaxy clusters and large-scale structure we see in the nearby Universe.
Astronomers do not yet understand what happened in the Universe between that point and now. How structure formed remains a topic at the forefront of science.
Our Observable Universe
This is the entire observable Universe for Earthlings. We have seen in these tutorials that the local Universe consists of galaxies, galaxy clusters, and superclusters of galaxies. These elements are the wave crests in the large-scale structure of the Universe. Between these galaxy-capped waves are the voids, where we see a lack of bright objects. Deeper into space, we look to earlier epochs in the Universe where we see quasars, early forms of galaxies with active cores perhaps from the continual interaction between galaxies in the early Universe. Beyond, we see the light left over from the Big Bang itself, this cosmic microwave background.
© 2002-2005 American Museum of Natural History
Last Modified: 2007-12-19 by Brian Abbott