> Mysterious New 'Dark Flow' Discovered in Space
> By Clara Moskowitz
> Staff Writer
> posted: 23 September 2008
> 12:46 pm ET
>
>
> As if the mysteries of dark matter and dark energy weren't vexing
> enough, another baffling cosmic puzzle has been discovered.
>
> Patches of matter in the universe seem to be moving at very high
> speeds and in a uniform direction that can't be explained by any of
> the known gravitational forces in the observable universe.
> Astronomers are calling the phenomenon "dark flow."
>
> The stuff that's pulling this matter must be outside the observable
> universe, researchers conclude.
>
> When scientists talk about the observable universe, they don't just
> mean as far out as the eye, or even the most powerful telescope,
> can see. In fact there's a fundamental limit to how much of the
> universe we could ever observe, no matter how advanced our visual
> instruments. The universe is thought to have formed about 13.7
> billion years ago. So even if light started travelling toward us
> immediately after the Big Bang, the farthest it could ever get is
> 13.7 billion light-years in distance. There may be parts of the
> universe that are farther away (we can't know how big the whole
> universe is), but we can't see farther than light could travel over
> the entire age of the universe.
>
> Mysterious motions
>
> Scientists discovered the flow by studying some of the largest
> structures in the cosmos: giant clusters of galaxies. These
> clusters are conglomerations of about a thousand galaxies, as well
> as very hot gas which emits X-rays. By observing the interaction of
> the X-rays with the cosmic microwave background (CMB), which is
> leftover radiation from the Big Bang, scientists can study the
> movement of clusters.
>
> The X-rays scatter photons in the CMB, shifting its temperature in
> an effect known as the kinematic Sunyaev-Zel'dovich (SZ) effect.
> This effect had not been observed as a result of galaxy clusters
> before, but a team of researchers led by Alexander Kashlinsky, an
> astrophysicist at NASA's Goddard Space Flight Center in Greenbelt,
> Md., found it when they studied a huge catalogue of 700 clusters,
> reaching out up to 6 billion light-years, or half the universe
> away. They compared this catalogue to the map of the CMB taken by
> NASA's Wilkinson Microwave Anisotropy Probe (WMAP) satellite.
>
> They discovered that the clusters were moving nearly 2 million mph
> (3.2 million kph) toward a region in the sky between the
> constellations of Centaurus and Vela. This motion is different from
> the outward expansion of the universe (which is accelerated by the
> force called dark energy).
>
> "We found a very significant velocity, and furthermore, this
> velocity does not decrease with distance, as far as we can
> measure," Kashlinsky told SPACE.com. "The matter in the observable
> universe just cannot produce the flow we measure."
>
> Inflationary bubble
>
> The scientists deduced that whatever is driving the movements of
> the clusters must lie beyond the known universe.
>
> A theory called inflation posits that the universe we see is just a
> small bubble of space-time that got rapidly expanded after the Big
> Bang. There could be other parts of the cosmos beyond this bubble
> that we cannot see.
>
> In these regions, space-time might be very different, and likely
> doesn't contain stars and galaxies (which only formed because of
> the particular density pattern of mass in our bubble). It could
> include giant, massive structures much larger than anything in our
> own observable universe. These structures are what researchers
> suspect are tugging on the galaxy clusters, causing the dark flow.
>
> "The structures responsible for this motion have been pushed so far
> away by inflation, I would guesstimate they may be hundreds of
> billions of light years away, that we cannot see even with the
> deepest telescopes because the light emitted there could not have
> reached us in the age of the universe," Kashlinsky said in a
> telephone interview. "Most likely to create such a coherent flow
> they would have to be some very strange structures, maybe some
> warped space time. But this is just pure speculation."
>
> Surprising find
>
> Though inflation theory forecasts many odd facets of the distant
> universe, not many scientists predicted the dark flow.
>
> "It was greatly surprising to us and I suspect to everyone else,"
> Kashlinsky said. "For some particular models of inflation you would
> expect these kinds of structures, and there were some suggestions
> in the literature that were not taken seriously I think until now."
>
> The discovery could help scientists probe what happened to the
> universe before inflation, and what's going on in those
> inaccessible realms we cannot see.
>
> The researchers detail their findings in the Oct. 20 issue of the
> journal Astrophysical Journal Letters.
>
