William Atkins
Monday, 03 November 2008 23:57
Science -
Space
Page 1 of 2
A peculiar movement of galaxy clusters through the universe is perplexing astronomers because it goes against the scientific assumption that the universe is homogeneous—that is, the universe is uniform throughout. It's being called: The Dark Flow!
The researchers studying this strangeness in the universe have been using x-ray radiation data provided in the early 1990s by the German space telescope
ROSAT (short for Röntgensatellit) and, later, from microwave radiation data taken from the NASA Wilkinson Microwave Anisotropy Probe (
WMAP).
What they found was about 700 galaxy clusters (a bunch of galaxies, which can number from around ten to thousands) all about one billion light-years away from Earth and all moving about 1,000 kilometers (600 miles) per second in the same direction.
These clusters, which the astronomers are calling "The Dark Flow," were all found moving in the general direction to a point in the southern sky.
A picture of the point, which was dubbed "the purple patch," is shown within the Science News article “
Galaxy on the move.”
The “purpose patch” is located between the constellations of Centaurus and Vela.
A article “
A Measurement of Large-Scale Peculiar Velocities of Clusters of Galaxies: Results and Cosmological Implications" published in
The Astrophysical Journal Letters, on October 20 2008, describes the “peculiar” action by these clusters.
Its authors--Alexander Kashlinsky, F. Atrio-Barandela, D. Kocevski, and H. Ebeling—state,
“Peculiar velocities of clusters of galaxies can be measured by studying the fluctuations in the cosmic microwave background (CMB) generated by the scattering of the microwave photons by the hot X-ray-emitting gas inside clusters. While for individual clusters such measurements result in large errors, a large statistical sample of clusters allows one to study cumulative quantities dominated by the overall bulk flow of the sample with the statistical errors integrating down."
And, added,
"We present results from such a measurement using the largest all-sky X-ray cluster catalog combined to date and the 3 yr WMAP CMB data. We find a strong and coherent bulk flow on scales out to at least 300 Mpc, the limit of our catalog. This flow is difficult to explain by gravitational evolution within the framework of the concordance ΛCDM model and may be indicative of the tilt exerted across the entire current horizon by far-away pre-inflationary inhomogeneities.”
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