Caption: A map of the cosmic microwave background radiation (CMB) made by the Wilkinson Microwave Anisotropy Probe (WMAP).
Dark matter and dark energy are two of the most mind-boggling ingredients in the universe. Ever since these concepts were first proposed, some astronomers have worked feverishly to figure out what each thing is, while other astronomers have tried to prove they don't exist, in hopes of restoring the universe to the more understandable place many would like it to be.
A new look at the data from one of the telescopes used to establish the existence of this strange stuff is causing some scientists to question whether they really exist at all. Yet other experts are holding firm to the idea that, whether we like it or not, the "dark side" of the universe is here to stay.
Dark matter is a proposed form of matter that could make up 22 percent of the universe's mass-energy budget, vastly outweighing all the normal matter, like stars and galaxies. Astronomers can't observe dark matter directly, but they think it's there because of the gravitational pull it seems to exert on everything else. Without dark matter, the thinking goes, galaxies would fly apart.
As if that weren't weird enough, scientists think another 74 percent of the mass-energy budget could be made of some strange quantity called dark energy. This force is thought to be responsible for the accelerating pace of the expansion of the universe. (For those keeping track, that would leave only a measly 4 percent of the universe composed of normal matter.)
Some cosmic background
One of the prime ways researchers tally how much these components contribute to the overall makeup of the universe is by measuring a dim glow of light pervading space that is thought to be left over from the Big Bang. The most detailed measurements yet taken of this radiation, which is called the cosmic microwave background (CMB), come from a spacecraft dubbed the Wilkinson Microwave Anisotropy Probe (WMAP).
"It's such an important thing the microwave background," said astrophysicist Tom Shanks of Durham University in England. "All the results in dark energy and dark matter in cosmology hang on it, and that?s why I'm interested in checking the results."
Recently Shanks and his graduate student Utane Sawangwit went back to examine the WMAP data and used a different method to calibrate how much smoothing, or blurring, the telescope was causing to its images. This smoothing is an expected affect, akin to the way Earth's atmosphere blurs stars' light so they twinkle.
Instead of using Jupiter as a calibration source, the way the WMAP team did, Shanks and Sawangwit used distant astronomical objects in the WMAP data itself that were emitting radio light.
"When we checked radio sources in the WMAP background, we found more smoothing than the WMAP team expected," Shanks told SPACE.com. "That would have big implications for cosmology if we were proven right."
If this smoothing error is larger than thought, it could indicate that fluctuations measured in the intensity of the CMB radiation are actually smaller than they originally appeared. The size of these fluctuations is a key parameter used to support the existence of dark matter and dark energy.
With smaller ripples, there would be no need to invoke exotic concepts like dark matter and dark energy to explain the CMB observations, Shanks said. The researchers will report their findings in an upcoming issue of the journal Monthly Notices of the Royal Astronomical Society.
Others not so sure
Yet other astronomers, particularly those who first analyzed the WMAP results, remain unconvinced.
"The WMAP team has carried out extensive checks and we unequivocally stand by our results," said WMAP principal investigator Charles Bennett of Johns Hopkins University in Baltimore, Md.
The WMAP researchers take issue with Sawangwit and Shanks' use of dim, far-away radio sources to calculate the telescope's smoothing error.
"These are weak sources, so many of them must be averaged together to obtain useful measurements. None of them move with respect to the CMB," said WMAP team member Mark Halpern of the University of British Columbia. "This method is inferior to our main approach."
Plus, Halpern said he and his colleagues had identified an error the other team made in failing to account for the confusing contribution of the CMB ripples themselves.
"We can obtain the Shanks result by omitting the step that properly accounts for the background confusion, but this step is necessary," Bennett explained.
Back in this corner ?
Yet Shanks said he's aware of these objections and stands by his calculations. "We don't think that's an issue," he said.
Ultimately, Shanks hopes future measurements of the microwave background radiation from new telescopes will help clear up the issue.
The European Space Agency's Planck spacecraft, launched into orbit in 2009, is currently taking new, even more detailed observations of the CMB.
"I'm very interested to see what Planck gets in terms of its results," Shanks said. "And of course we will be there to try and keep everybody as honest as possible. We're hoping we can use our methods in the same way to check their beam profile that they ultimately come up with."
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