The Milky Way—and everything in it—exists in an enormous void in space that is largely lacking stars, galaxies and planets.
This is according to new evidence presented by scientists from the University of Wisconsin-Madison, who say our presence within one of these empty regions would help explain a lot of problems relating to astronomy—specifically the rate at which the universe appears to be expanding.
In 2013, the scientists, led by astronomer Amy Barger, discovered that the Milky Way appears to be located in a large void in space. These voids look a bit like the holes in Swiss cheese. They have fewer stars and galaxies than other regions—and because there is less matter, they exert a smaller gravitational pull on the surrounding space.
The team has now presented its latest findings relating to the void at the meeting of the American Astronomical Society in Austin, Texas.
In their presentation, they showed how our existence inside a void helps explain discrepancies within various measurements of the Hubble Constant—the unit scientists use to describe the rate the universe is expanding. It is done by measuring the distance between supernova (exploding stars) or by measuring light from just after the Big Bang—the cosmic microwave background (CMB).
At present, the rate is estimated to be 70.4 kilometres (43.7 miles) per second per megaparsec. A megaparsec is a million parsecs, and one parsec is about 3.26 light years. So the Hubble Constant is very fast.
However, different techniques used to make accurate measurements of it produce slightly differing results.
“No matter what technique you use, you should get the same value for the expansion rate of the universe today,” Ben Hoscheit, who presented the research, said in a statement. “Fortunately, living in a void helps resolve this tension.”
The void helps because the gravitational pull would lead to slightly different results when taking measurements of the light from supernova. However, it would have no effect on the value we get from the CMB.
Researchers say the void in which we reside—the KBC void—is seven times bigger than normal voids, with a radius of around one billion light years. It is spherical and has a shell of galaxies, stars and other matter. The initial measurements of the void from 2013 match up with discrepancies within the Hubble Constant.
The team concludes there are no observational obstacles to say the Milky Way does not exist in a huge void.
“It is often really hard to find consistent solutions between many different observations,” Barger said. “What Ben has shown is that the density profile [of the void] is consistent with cosmological observables. One always wants to find consistency, or else there is a problem somewhere that needs to be resolved.”