More than ten years ago, while taking the temperature of the universe, astronomers found something odd. They discovered that a patch of sky, spanning the width of 20 moons, was unusually cold.

The astronomers were measuring the microwave radiation that bathes the entire universe, a glowing relic of the big bang. To gaze at this cosmic microwave background, or CMB, is to glimpse the primordial universe, a time when it was less than 400,000 years old.

What's now emerging as the top hypothesis is a cosmic supervoid

The CMB blankets the sky, and looks pretty much the same everywhere, smoldering at a feebly cold temperature of 2.725 degrees Kelvin - just a couple degrees warmer than absolute zero. But armed with the newly launched WMAP satellite, the astronomers had set out to probe temperature variations as tiny as one part in 100,000. Born from the quantum froth that was the universe a half-moment after the big bang, those random fluctuations help scientists understand what the cosmos is made of and how it all came to be.

More data would help. For instance, more observations will allow astronomers to get more accurate measurements of the supervoid's size and properties. They might also reveal whether there's a smaller void in the foreground, which could help cool the CMB. Perhaps, the cold spot is so frigid because the supervoid also happens to be in front of a region of the CMB that's already a bit colder than normal.

Even though the numbers don't add up now, it's no reason to fret. "At this point, because the uncertainties are so large, one should not lose much sleep over this," says Carlos Frenk, an astrophysicist at the University of Durham in the UK. His hunch is that with more data and analysis, the supervoid will emerge as the correct answer. "It could very well be that it all falls into place quite neatly," he says.

How the creation of the universe produced the CMB (Credit: NASA/WMAP Science Team)

If so, the cold spot will represent the first measurement of an object - a supervoid - leaving an imprint on the CMB via the ISW effect. That's significant partly because the supervoid is simply so huge. The supervoid could be important in another way: "We have one more way to study dark energy, which is the weirdest thing in the universe," Szapudi says.

The ISW effect only works because the universe expands faster and faster, and the mysterious force pushing the cosmos apart is dark energy. By measuring the ISW effect from the supervoid, researchers can probe dark energy's influence - and better understand how it behaves and what it is.

But for now, the mystery of the cold spot continues. "We just don't know the end of the story," Frenk says. "I don't think anybody knows."

The full story and origin: BBC Bizarre Cosmic Objects