Is an Adjacent Universe Causing the Dark Flow of Hundred of Millions of Stars at the Edge of the Observable Universe? Or, Might It Be Something Else
Back in the Middle Ages, maps showed terrifying images of sea dragons at the boundaries of the known world. Today, scientists have observed strange new motion at the very limits of the known universe -- kind of where you'd expect to find new things, but they still didn't expect this. A huge swathe of galactic clusters seem to be heading to a cosmic hotspot and nobody knows why.
"The clusters show a small but measurable velocity that is independent of the universe's expansion and does not change as distances increase," says lead researcher Alexander Kashlinsky at NASA's Goddard Space Flight Center. "We never expected to find anything like this."
Kashlinsky calls this collective motion a "dark flow" in the vein of more familiar cosmological mysteries: dark energy and dark matter. "The distribution of matter in the observed universe cannot account for this motion," he says, keeping to the proven astrophysical strategy of calling anything we don't understand "dark."
Hot X-ray-emitting gas in a galaxy cluster scatters photons from the cosmic microwave background. Clusters don't precisely follow the expansion of space, so the wavelengths of scattered photons change in a way that reflects each cluster's individual motion.
This results in a minute shift of the microwave background's temperature in the cluster's direction. Astronomers refer to this change as the kinematic Sunyaev-Zel'dovich (SZ) effect.
A related distortion, known as the thermal SZ effect, has been observed in galaxy clusters since the 1980s. But the kinematic version is less than one-tenth as strong and has not been detected in any cluster.
A black hole can't explain the observations -- objects would accelerate into the hole, while the NASA scientists see constant motion over a vast expanse of a billion light-years. You have no idea how big that is. This is giant on a scale where it's not just that we can't see what's doing it, it's that the entire makeup of the universe as we understand it can't be right if this is happening.
Such discoveries force a whole new set of ideas onto the table which, even if they turn out to be wrong, are the greatest ways to advance science and our understanding of everything. One explanation that's already been offered is that our universe underwent a period of hyper-inflation early in its existence, and everything we think of as the vast and infinite universe is actually a small corner under the sofa of the real expanse of reality. Which would be an amazing, if humbling, discovery.
Now, a new study from the University at Buffalo contradicts the dark flow theory, showing that exploding stars in different parts of the universe do not appear to be moving in sync. Working with data on 557 such stars, called supernovae, UB scientists deduced that while the supernovae closest to Earth all shared a common motion in one direction, supernovae further out were heading somewhere else. An article announcing the research results will appear in a forthcoming edition of the peer-reviewed Journal of Cosmology and Astroparticle Physics.
In 2008, a research team led by a NASA scientist announced a startling discovery: Clusters of galaxies far apart from one another appeared to be traveling in the same direction, contradicting as we pointed out above, the standard model of the universe -- which predicts that, as a whole, mass within our universe should flow randomly in all directions, relative to the background radiation of the cosmos.
The one-way "dark flow" that the NASA-led group discovered created a mystery. What could account for the unexpected motion? Maybe another universe existed beyond the bounds of ours, dragging our stars ever closer through the pull of gravity.
Then again, maybe not. A new study from the University at Buffalo contradicts the dark flow theory, showing that exploding stars in different parts of the universe do not appear to be moving in sync.
Working with data on 557 such stars, called supernovae, UB scientists deduced that while the supernovae closest to Earth all shared a common motion in one direction, supernovae further out were heading somewhere else. The difference in motion became pronounced for stars 680 million or more light years away from Earth.
An article announcing the research results will appear in a forthcoming edition of the peer-reviewed Journal of Cosmology and Astroparticle Physics.
Though the findings disagree with the "dark flow" hypothesis, they coincide with the predictions of another model of the universe: Lambda-Cold Dark Matter, the standard model of cosmology.'
"Our result is boring, in a way, because it matches your expectation for the standard cosmological model," said UB physicist William Kinney. "If it turns out that the NASA team led by Alexander Kashlinsky is right, it would be exciting because there would be some crazy thing going on that nobody understood. There would have to be something very radical, like a big mass outside of our universe that's pulling on stuff inside our universe. That would be big news."
"But our data do not match theirs," Kinney continued. "With our study, we're muddying the water. It's not yet clear who is right. We have to do more figuring to build up a more detailed and accurate picture of the universe."
Kinney, an associate professor, completed the study on supernovae with De-Chang Dai, a UB postdoctoral researcher who has since joined the University of Cape Town, and Dejan Stojkovic, an assistant professor of physics at UB.
The supernova data the team used to complete their study came from the Union2 data set, which the Supernova Cosmology Project at the Lawrence Berkeley National Laboratory released in 2010. Though Union2 incorporates astronomical observations from different telescopes and different times, the data set controls carefully for systematic bias and serves as a useful check for the possible presence of systematic errors in the work of Kashlinsky and others, Kinney said.
The Daily Galaxy via University at Buffalo and sciencedaily.com