Astronomers observing a distant region of space say they have discovered something truly remarkable: a whole lot of nothing.

The enormous void, nearly a billion light years across, is empty of normal matter such as stars, gas and galaxies. It's even without dark matter — the mysterious unseen mass often inferred from observations of regions outside our solar system.

And while it's not the first void to be discovered in the universe, it is the largest, said Lawrence Rudnick of the University of Minnesota.

"Not only has no one ever found a void this big, but we never even expected to find one this size," said Rudnick, who reported his findings along with Shea Brown and Liliya Williams, also of the University of Minnesota, in a paper accepted for publication in the Astrophysical Journal.

"What we've found is not normal, based on either observational studies or on computer simulations of the large-scale evolution of the universe," Williams said.

"It looks like something to be taken seriously,” said Brent Tully, a University of Hawaii astronomer who wasn't part of this research but studies a smaller void closer to Earth. Tully said while astronomers may eventually find a few galaxies or structures in the void, it would still be mostly empty.

The astronomers were able to see the void in a region of sky in the constellation Eridanus first from measurements of the number of galaxies and then by comparing those results to the region's cosmic microwave background, the faint radiation left over from the Big Bang that gave birth to the Universe.

Since the photon particles that make up cosmic microwaves tend to gain energy (and thus heat up) when they pass through matter, the temperature of this background radiation can change ever so slightly depending on how much matter is present in a region.

Using the Very Large Array radio telescope in New Mexico, the astronomers were able to measure the drop in the number of galaxies in the region. Subsequent observations from a NASA satellite designed to measure cosmic microwave background temperature changes as small as a millionth of a degree confirmed the findings: the region was a "cold spot."

"Although our surprising results need independent confirmation, the slightly colder temperature of the CMB in this region appears to be caused by a huge hole devoid of nearly all matter roughly six to 10 billion light-years from Earth," Rudnick said in a statement.