Dark flow
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Dark Flow is a name given to a net motion of galaxy clusters with respect to the cosmic microwave background radiation which was found in a 2008 study. According to standard cosmological models, the motion of galaxy clusters with respect to the cosmic microwave background should be randomly distributed in all directions. However, analyzing the three-year WMAP data using the kinematic Sunyaev-Zel'dovich effect, the authors of the study found evidence of a common motion of at least 600 km/s toward a 20-degree patch of sky between the constellations of Centaurus and Vela.
The authors (A. Kashlinsky, F. Atrio-Barandela, D. Kocevski, and H. Ebeling) suggest that the motion may be a remnant of the influence of no-longer-visible regions of the universe prior to inflation. Telescopes cannot see events earlier than about 380,000 years after the big bang, when the universe became transparent (the Cosmic Microwave Background); this corresponds to the particle horizon at a distance of about 46 billion (4.6×1010) light years. Since the matter causing the net motion in this proposal is outside this range, it would in a certain sense be outside our visible universe; however, it would still be in our past light cone.
The results appear in the October 20, 2008, issue of Astrophysical Journal Letters, which is available online. The authors state that they plan to extend their analysis to additional clusters and the recently released WMAP five-year data.[1][2][3][4]
Criticisms
Astrophysicist Ned Wright posted an online response to the study arguing that its methods are flawed.[5] The authors of the "dark flow" study released a statement in return, refuting three of Wright's five arguments and identifying the remaining two as a typo and a technicality that do not affect the measurements and their interpretation.[6]
A more recent statistical work done by Ryan Keisler [7] claims to rule out the possibility that the dark flow is a physical phenomenon because Kashlinsky et al. do not consider primary CMB anisotropies as important as they are.
In March of 2010 it was reported by Discovery News that NASA's Goddard Space Center confirmed this could be the effects of a sibling universe or a region of space-time fundamentally different from the observable universe. Data on more than 1,000 galaxy clusters have been measured, including some as distant as 3 billion light-years. Alexander Kashlinksy claims these measurements show the universe's steady flow is clearly not a statistical fluke. Said Kashlinsky: "At this point we don't have enough information to see what it is, or to constrain it. We can only say with certainty that somewhere very far away the world is very different than what we see locally. Whether it's 'another universe' or a different fabric of space-time we don't know."[8]
See also
References
- ^ A. Kashlinsky, F. Atrio-Barandela, D. Kocevski, and H. Ebeling, A measurement of large-scale peculiar velocities of clusters of galaxies: results and cosmological implications (same paper at nasa.gov)
- ^ A. Kashlinsky, F. Atrio-Barandela, D. Kocevski, and H. Ebeling, A measurement of large-scale peculiar velocities of clusters of galaxies: technical details (same paper at nasa.gov)
- ^ Press release from Goddard Space Center
- ^ Press release by the University of Hawai`i
- ^ Item in Ned Wright's News of the Universe
- ^ Refutation of Wright's remarks
- ^ The Statistical Significance of the "Dark Flow" 22 Oct 2009
- ^ Mysterious 'Dark Flow' May Be Tug Of Other Universe
External links
- "Mysterious New 'Dark Flow' Discovered in Space", Space.com
- "Hints of structure beyond the visible universe", New Scientist, 10 Jun 2008
- "Galaxies on the move: Scientists detect a mysterious flow of galactic clusters", Science News, Vol.174, p. 12, Oct. 25, 2008.
- "Dark flow: Proof of another universe? - Subscription required" New Scientist, 23 January 2009
- "New Proof Unknown "Structures" Tug at Our Universe", National Geographic, 22 Mar 2010