Outlined in light blue, giant collections of galaxies can be divided up into superclusters. But our supercluster, along with many nearby ones, might still reside in an even larger cosmic void. Image credit: R. Brent Tully, Hélène Courtois, Yehuda Hoffman & Daniel Pomarède, Nature 513, 71–73 (04 September 2014).

We’re way below average! Astronomers say Milky Way resides in a great cosmic void

What we think of as our average region of the Universe might not be average at all.

“No matter what technique you use, you should get the same value for the expansion rate of the universe today.” -Ben Hoscheit

If you went to give our cosmic address, you might tell someone that we lived on planet Earth, orbiting our Sun, on the outskirts of a spur of the Milky Way’s spiral arms, in the second largest galaxy in our local group, about 50 million light years from the Virgo Cluster, embedded within the Laniakea supercluster. Well, you might have to add another line to that address, as Laniakia, along with dozens of other nearby giant clusters, is all embedded within a great cosmic void stretching a billion light years from end-to-end. This below-average region of space is consistent with everything we observe, supported by new observations presented at this week’s American Astronomical Society meeting, and just might provide the solution to one of the Universe’s greatest discrepancies.

The simulated large-scale structure of the Universe shows intricate patterns of clustering that never repeat. But from our perspective, we can only see a finite volume of the Universe, which appears uniform on the largest scales. Image credit: V. Springel et al., MPA Garching, and the Millenium Simulation.