Synopsis: Emptiness Constrains the Universe

The distribution of galaxies around regions of relatively empty space can be used to constrain cosmological parameters.
Synopsis figure
N. Hamaus/Ludwig Maximilian University of Munich

Viewed on the scale of hundreds of millions of light years, galaxies in the Universe are clustered into sheets, filaments, and groups that are separated by relatively empty space known as cosmic voids. Now, a team led by Nico Hamaus at the Ludwig Maximilian University of Munich has studied the statistical distribution of galaxies around cosmic voids to constrain two key cosmological parameters that describe the Universe. Cosmological studies have largely neglected to collect such data from low-density regions like voids. But because galactic motion in these regions is less chaotic than in denser parts of the Universe, it can be more reliably modeled.

The team analyzed a galaxy map from the Sloan Digital Sky Survey to determine the spatial distributions of galaxies near cosmic voids. If the Universe is homogenous and isotropic (as physicists believe it to be), then the distribution of galaxies located parallel and perpendicular to the line of sight should be the same. But the researchers found differences between the two groups, even after correcting for the effects of galaxy motion. Knowing that such apparent distortions depend on the Universe’s history and geometry, they iteratively tested parameters in a model of the Universe’s expansion until the model described the observations.

Using this approach, Hamaus and his colleagues estimated the Universe’s average matter fraction and the growth rate of structure. They determined that the value of this latter parameter, which quantifies the strength of the gravitational force, agrees with expectations from general relativity. Their analysis provides a robust test of Einstein’s theory since deviations predicted by alternative models would be most pronounced in low-density environments.

This research is published in Physical Review Letters.

–Katherine Kornei

Katherine Kornei is a freelance writer based in Portland, Oregon.


More Features »


More Announcements »

Subject Areas


Previous Synopsis

Next Synopsis

Industrial Physics

Get the Hydrogen Out

Read More »

Related Articles

Viewpoint: Neutron-Star Implosions as Heavy-Element Sources

Viewpoint: Neutron-Star Implosions as Heavy-Element Sources

A dramatic scenario in which a compact black hole eats a spinning neutron star from inside might explain a nearby galaxy’s unexpectedly high abundance of heavy elements. Read More »

Viewpoint: Spinning Black Holes May Grow Hair

Viewpoint: Spinning Black Holes May Grow Hair

A spinning black hole may lose up to 9% of its mass by spontaneously growing “hair” in the form of excitations of a hypothetical particle field with a tiny mass. Read More »

Synopsis: A Reionization Filter for the Cosmic Microwave Background

Synopsis: A Reionization Filter for the Cosmic Microwave Background

A new method of analyzing cosmic microwave background data could isolate signatures from the so-called reionization period that occurred a few hundred million years after the big bang. Read More »

More Articles