How do astrophysicists weigh the universe

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Bochum cosmologists led by Prof. Dr. Hendrik Hildebrandt won. Several years ago Hildebrandt was part of a research consortium that had drawn attention to discrepancies in the data between different groups. The determined values ​​for matter density and structure differed depending on the measurement method. A new analysis that included additional infrared data made the differences even clearer. You might point out that the standard model of cosmology is flawed.

The science magazine Rubin of the Ruhr University Bochum reports on Hendrik Hildebrandt's research. The latest analysis by the research consortium called the Kilo-Degree Survey appeared in January 2020 in the journal Astronomy and Astrophysics.

Two methods of determining the structure of matter

Research teams can calculate the density and structure of matter based on the cosmic microwave background, radiation that was emitted shortly after the Big Bang and can still be measured today. This is the procedure used by the Planck research consortium.

The team of the Kilo-Degree Survey, and some other groups, determined the density and structure of matter with the help of the gravitational lensing effect: Massive objects deflect light from galaxies, so that these galaxies, when viewed from Earth, appear with a distorted shape in a different place than they actually are. From these distortions, cosmologists can infer the mass of the distracting objects and thus the total mass of the universe. To do this, however, they need to know, among other things, the distances between the light source, the distracting object and the observer. The researchers determine this in turn with the help of the redshift, which means that the light from galaxies further away arrives on Earth shifted to the red.

New calibration using infrared data

In order to determine distances, cosmologists therefore take pictures of the galaxies at different wavelengths, for example one in the blue, one in the green and one in the red range; then they determine the brightness of the galaxies in the various images. Hendrik Hildebrandt and his team also include several images from the infrared range, which improves the precision of the distance determination.

Earlier analyzes had already shown that the data from the Planck Consortium based on the microwave background systematically deviated from the gravitational lens effect data. Depending on the data set, the deviation was more or less pronounced, most pronounced in the Kilo-Degree Survey. "Our data set is the only one that is based on the gravitational lensing effect and is calibrated with additional infrared data," says Hendrik Hildebrandt, Heisenberg professor and head of the observing cosmology working group in Bochum. "That could be the reason for the greater deviation from the Planck data."

To check this discrepancy, the group evaluated the data set from another research consortium, the Dark Energy Survey, using a similar calibration. As a result, these values ​​also moved further away from the Planck values.

Discussion in professional circles

Scientists are currently debating whether the discrepancy between the data sets is actually an indication that the standard model of cosmology is wrong or not. The Kilo-Degree Survey team is already working on a new analysis of a more extensive data set that could provide further insights. It is expected that in spring 2020 they will be able to provide even more precise data for matter density and structure.

Detailed article in ruby

You can find a detailed article on the topic in the science magazine Rubin. Texts on the website and images from the download area may be used free of charge for editorial purposes provided the copyright is indicated.

Hendrik Hildebrandt et al .: KiDS + VIKING-450: Cosmic shear tomography with optical and infrared data, in: Astronomy & Astrophysics, 2020, DOI: 10.1051 / 0004-6361 / 201834878

Prof. Dr. Hendrik Hildebrandt
Working group observational cosmology
Faculty of Physics and Astronomy
Ruhr-University Bochum
Tel .: +49 234 32 24019
Email: [email protected]