Our universe is not uniform. Its matter is clumped up in various places, with some regions less dense than others. And it seems like we just might be in one of those places, a vast cosmic void.
A new study was presented today at the 230th meeting of the American Astronomical Society in Texas suggesting as much. It provides new evidence that our region of space has far fewer galaxies, stars, and planets than others. Two papers on the findings have been submitted to the Astrophysical Journal.
The idea that we live in a void neatly explains a problem in astrophysics. When we measure the expansion rate of the universe, the Hubble Constant, it should be the same everywhere we look. But as it’s not, this suggests the gravitational pull elsewhere in the universe is stronger.
“No matter what technique you use, you should get the same value for the expansion rate of the universe today,” said Ben Hoscheit from the University of Wisconsin-Madison, the study’s lead author, in a statement. “Fortunately, living in a void helps resolve this tension.”
According to the findings, the spherical void we reside in is seven times larger than the average void, spanning a huge 1 billion light-years. Named KBC after its discoverers (Keenan, Barger, and Cowie) in 2013, it is the largest void we’ve ever found.
That’s not to say it definitely exists, just that it seems plausible. Most of the evidence comes from discrepancies in the expansion of the universe on a local scale and on a cosmic scale. The former comes from supernova explosions in our vicinity, the latter from photons originating from the cosmic microwave background (CMB).
The void affects the value for the Hubble Constant measured on a local scale, but not a cosmic one. This gives rise to the discrepancy for the two readings, and provides some indirect evidence for the void’s existence.
Hoscheit told IFLScience the difference was about 73.24 kilometers (45.5 miles) per second per megaparsec at the local level, and 66.93 at a cosmic level.
“If one does not account for the effects associated with living in this void, one is biased to measure a higher value of this Hubble constant 'locally',” he said.
It’s no secret that our universe is inherently lumpy. Our galaxy resides in the vast Laniakea Supercluster, a gravitationally-bound web of 100,000 galaxies. Superclusters like this are the biggest structures in the universe. We appear to be pulled towards a dense region called the Great Attractor, and pushed away from an emptier region called the Dipole Repeller.
Whether we’re being pushed or pulled, it does look like we may now also be in a decidedly empty region of space. Fortunately for us on Earth, it’s not enough to make our observations of the universe any less impressive.