Mysterious dance of dwarfs may force a cosmic rethink
- July 24, 2014
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A finding that many small galaxies don't “swarm” around larger ones like bees but rather circle them in disc-shaped orbits is creating a new conundrum for scientists.
Last year “we announced our startling discovery that half of the dwarf galaxies surrounding the Andromeda Galaxy are orbiting it in an immense plane,” said physicist Geraint Lewis from the University of Sydney in Australia. “This plane is more than a million light years in diameter, but is very thin, with a width of only 300,000 light years.”
Now, astronomers are extending the finding to other galaxies.
The universe contains billions of galaxies. Some, such as the Milky Way, are immense, containing hundreds of billions of stars. Most galaxies, however, are dwarfs, much smaller and with only a few billion stars. For decades astronomers have used computer models to predict how these dwarf galaxies should orbit large galaxies. They had always found that they should be scattered randomly.
“Our Andromeda discovery did not agree with expectations, and we felt compelled to explore if it was true of other galaxies throughout the universe,” said Lewis. Using the Sloan Digital Sky Survey, a resource of color images and 3-D maps covering more than a third of the sky, the researchers dissected the properties of thousands of nearby galaxies.
“We were surprised to find that a large proportion of pairs of satellite galaxies have oppositely directed velocities if they are situated on opposite sides of their giant galaxy hosts,” said Neil Ibata of the Lycée International in Strasbourg, France, lead author of a new study on the findings, published July 20 in the journal Nature.
“Everywhere we looked we saw this strangely coherent coordinated motion of dwarf galaxies. From this we can extrapolate that these circular planes of dancing dwarfs are universal, seen in about 50 percent of galaxies,” said Lewis. “This is a big problem that contradicts our standard cosmological models. It challenges our understanding of how the universe works including the nature of dark matter,” an unseen material that is detected through its gravity.
The researchers believe the answer may be hidden in some currently unknown physical process that governs how gas flows in the universe. Some experts have made more radical suggestions, including bending and twisting the laws of gravity and motion. “Throwing out seemingly established laws of physics is unpalatable,” said Professor Lewis, “but if our observations of nature are pointing us in this direction, we have to keep an open mind. That's what science is all about.”
source : http://www.world-science.net