OSU: Astronomers Use Empty Space to Study the Universe

[bystander]

Much Ado about Nothing: Astronomers Use Empty Space to Study the Universe
Ohio State University | 2016 Aug 11

A lot of information contained in cosmic voids, study suggests

[img3="This simulation of the large-scale structure of the universe reveals the cosmic web of galaxies and the vast, empty regions known as voids. Image by Nico Hamaus, Universitäts-Sternwarte München, courtesy of The Ohio State University."]https://news.osu.edu/assets/image-cache ... 24d4b5.jpg[/img3][hr][/hr]

Researchers who are looking for new ways to probe the nature of gravity and dark energy in the universe have adopted a new strategy: looking at what’s not there.

In a paper to appear in upcoming issue of Physical Review Letters, the international team of astronomers reports that they were able to achieve four times better precision in measurements of how the universe’s visible matter is clustered together by studying the empty spaces in between.

Paul Sutter, study co-author and staff researcher at The Ohio State University, said that the new measurements can help bring astronomers closer to testing Einstein’s general theory of relativity, which describes how gravity works.

Sutter likened the new technique to “learning more about Swiss cheese by studying the holes,” and offered another analogy to explain why astronomers would be interested in the voids of space.

“Voids are empty. They’re boring, right? Galaxies are like the cities of the universe, full of bright lights and activity, and voids are like the miles and miles of quiet farmland in between,” Sutter explained.

“But we’re looking for bits of evidence that general relativity might be wrong, and it turns out that all the activity in galaxies makes those tiny effects harder to see. It’s easier to pick up on effects in the voids, where there’s less distraction—like it’s easier to spot the glimmer of a firefly in a dark cornfield than in a lit-up city bustling with nightlife.”

The voids, he pointed out, are only empty in the sense that they contain no normal matter. They are, in fact, full of invisible dark energy, which is causing the expansion of the universe to accelerate. ...

Constraints on Cosmology and Gravity from the Dynamics of Voids - Nico Hamaus et al

• arXiv.org > astro-ph > arXiv:1602.01784 > 04 Feb 2016

[Ann]

Nico Hamaus, Alice Pisani, Paul M. Sutter, Guilhem Lavaux, Stéphanie Escoffier, Benjamin D. Wandelt and Jochen Weller wrote:
These measurements are robust to a battery of consistency tests. They improve on existing constraints by accessing smaller-scale clustering information in galaxy surveys through an accurate model of non-linear dynamics in void environments. As such, our analysis furnishes a powerful probe of deviations from Einstein's general relativity in the low density regime which has largely remained untested so far. We find no evidence for such deviations in the data at hand.

Translation: Even the voids fail to chip away at Einstein's general relativity.

Ann

[bystander]

Synopsis: Emptiness Constrains the Universe
American Physical Society | Physics | 2016 Aug 25

The distribution of galaxies around regions of relatively empty space can be used to constrain cosmological parameters.

[img3="Credit: N. Hamaus/Ludwig Maximilian University of Munich"]http://d22izw7byeupn1.cloudfront.net/jo ... 117.091302[/img3][hr][/hr]

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.

Cosmology: Lore of Lonely Regions
Ludwig Maximilian University of Munich | 2016 Aug 16

Constraints on Cosmology and Gravity from the Dynamics of Voids - Nico Hamaus et al

• Physical Review Letters 117(9):091302 (26 Aug 2016) DOI: 10.1103/PhysRevLett.117.091302
  arXiv.org > astro-ph > arXiv:1602.01784 > 04 Feb 2016