Friday, December 21, 2007

Bullet Cluster

A purple haze shows dark matter flanking the "Bullet Cluster." Image Credit: X-ray: NASA/CXC/M.Markevitch et al. Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al. Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al

The amount of matter, or "mass," in a galaxy is made up mostly of the gas that surrounds it. Stars, planets, moons and other objects count too, but a majority of the mass still comes from the hot, glowing clouds of hydrogen and other gases.

When the Bullet Cluster's galaxies crossed and merged together, their stars easily continued on their way unscathed. This may seem a bit perplexing, because the bright light of stars makes them appear enormous and crowded together. It would be easy to expect them to smash into each other during their cosmic commute. But the truth is, stars are actually spaced widely apart and pass harmlessly like ships on an ocean.

The gas clouds from the merging galaxies, however, found the going much tougher. As the clouds ran together, the rubbing and bumping of their gas molecules caused friction to develop. The friction slowed the clouds down, while the stars they contained kept right on moving. Before long, the galaxies slipped out of the gas clouds and into clear space.

With the galaxies in open space, Chandra scientists found dark matter hiding.

We can make certain conclusion about our universe given some insight into the geometric way our universe as a whole exists now?

Lets first look at what Sean Carroll has to say and then we can go from here.

The Cosmological Constant

Sean M. Carroll
Enrico Fermi Institute and Department of Physics
University of Chicago
5640 S. Ellis Ave.
Chicago, IL 60637, U.S.A.


This is a review of the physics and cosmology of the cosmological constant. Focusing on recent developments, I present a pedagogical overview of cosmology in the presence of a cosmological constant, observational constraints on its magnitude, and the physics of a small (and potentially nonzero) vacuum energy.

What better way to speak to the content of the universe if you cannot look at the way it is now. It's current "geometric implication" as a result of the parameters we have deduced with WMAP, and resulting information on the content of the dark matter/energy within the universe?

See:The Cosmological Parameters

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