Last year astrophysicists were shocked to discover that there was apparently a giant unexplained hole in the cosmos, which was going to force them to rewrite their theories about structure formation in the universe, since no current theory of cosmology could explain the gaping void. Some astrophysicists believed it was an imprint of another universe.
It was an exciting discovery that stirred up a lot of debate and questions about the nature of the universe, but now it turns out that the gaping hole may never really have existed. After re-examining the area, which supposedly contained far fewer stars and galaxies than it should, could be nothing more than a statistical artifact (a.k.a. coincidence).
The apparent hole was first spotted by Lawrence Rudnick and colleagues at the University of Minnesota in Minneapolis. Rudnick was intrigued by a different discovery: a cold spot in the cosmic microwave background measured by the WMAP spacecraft. Using data from the Very Large Array telescope at the National Radio Astronomy Observatory near Socorro, New Mexico, Rudnick studied the area and came to a startling conclusion: The mysterious cold spot coincided with a void almost 1 billion light years across, the largest ever heard of.
The story quickly made headlines such as “Gaping Hole in Outer Space”, which no one could explain. But the latest analysis of the area casts some doubt on Rudnick’s conclusion. It’s all a matter of interpretation, says Kendrick Smith, an astronomer at the University of Cambridge. Smith’s work with Dragan Huterer of the University of Michigan, Ann Arbor, suggests that Rudnick may have misjudged. They will submit a paper on the matter to the Monthly Notices of the Royal Astronomical Society.
They reason that since there will always be some stars in front of any cosmic hole, and others behind it, a void cannot actually be seen with the naked eye. Therefore it is all inferred statistically. Smith and Huterer question Rudnick’s assertions in two ways. The cold spot, they says, and the alleged void don’t actually coincide perfectly but have different centers. Secondly, Smith claims that the Minnesota group made choices that allowed them to “see” the void by focusing only on the portion of the cold spot with the fewest galaxies and by including only galaxies above a certain luminosity in their count.
Smith and Huterer claim that by making equally valid (though different) choices regarding the luminosity cut-off and the area of the cold spot to concentrate on, you can make the void disappear. Smith says, you can even find a region with an unusually high number of galaxies within the cold spot with the same degree of statistical significance. Since Rudnick’s paper did acknowledge certain “statistical uncertainties”, this news doesn’t come as a huge surprise for some.
“I think Smith and Huterer have made a good case that there is no void in the radio data at this location,” says WMAP theorist David Spergel of Princeton University.
Astronomer Eiichiro Komatsu, at the University of Texas at Austin, says there is a way to settle the matter by pointing an optical telescope at the cold spot and counting the number of galaxies at different distances you could then construct a 3D map and see more clearly whether there is a large empty patch or not.
But whether or not the void itself is real, Komatsu says, “there is still this mysterious cold spot that we’d like to learn more about”.
Posted by Rebecca Sato
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