May 23, 2011

The Milky Way Is A Rare Type Of Galaxy

Stanford University astrophysicist Risa Wechsler andother researchers have found that only four percent of galaxies are similar to the Milky Way galaxy.

The team compared the Milky Way to similar galaxies in terms of luminosity and distance to other bright galaxies.  They found that galaxies with two satellites that are as bright and close by as the Milk Way's two closest satellites, the Large and Small Magellanic Clouds, are hard to come by.

According to a press release by the National Science Foundation (NSF), the team studied over 20,000 galaxies with properties similar to the Milky Way and investigated the galaxies surrounding these Milky Way "twins" to create a "census" of galaxies similar to the Milky Way in the universe.

"We are interested in how the Milky Way fits into the broader context of the universe", Wechsler said in an NSF press release. "This research helps us understand whether our galaxy is typical or not, and may provide clues to its formation history."

Wechsler and the other researchers performed computer simulations to try and recreate the universe from specific sets of starting conditions. 

They compared their simulations with data from the Sloan Digital Sky Survey (SDSS) in order to try and learn more about possible conditions in the early universe.  The team was able to test different theories of galaxy formation to determine whether or not each would result in a universe that matches what is in the sky today.

"This is an excellent example of data-enabled science," Nigel Sharp, of NSF's Division of Astronomical Sciences, said in the press release. "Comparing the 'fake' and 'real' Universes is how we discriminate between successful and unsuccessful theories. This work interconnects three of the four legs of science: theory, observation and simulation, for a powerful scientific result."

The researchers' results support a leading theory of galaxy formation known as the Cold Dark Matter (CDM) theory.  This theory assumes that most of the matter in the Universe consists of material that cannot be observed by its electromagnetic radiation and whose constituent particles move slowly. 

"Because the presence of two galaxies like the Magellanic Clouds is unusual, we can use them to learn more about our own galaxy," Wechsler said in the press release.

The team used their simulation to identify a number of simulated galaxies that had satellites matching the Milky Way's.

"Future surveys will allow us to extend this study to even dimmer satellite galaxies, to build a full picture of the formation of our galaxy," said Wechsler.

Results of the study were published in the May 20 issue of the Astrophysical Journal


Image Caption: This image, taken from a visualization created by the Advanced Visualization Laboratory at the National Center for Supercomputing Applications (NCSA), shows the formation of the Milky Way galaxy at 16 million to 13.7 billion years old. Brian O'Shea of Michigan State University (formerly of Los Alamos National Laboratory) and Michael Norman of the University of California at San Diego collaborated on this research. Credit: National Center for Supercomputing Applications


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