From Ruhr Universität Bochum: “The weight of the Universe”

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From Ruhr Universität Bochum

28 April 2020
Julia Weiler (jwe)

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The Universe contains unimaginably many objects. Cosmologists are trying to weigh them all.
Credit: © ESO/T. Preibisch

Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

The weight of the Universe

New results from physicists in Bochum have challenged the Standard Model of Cosmology.

Results from physicists in Bochum have challenged the Standard Model of Cosmology. Infrared data, which have recently been included in the analysis, could be decisive.

Bochum cosmologists headed by Professor Hendrik Hildebrandt have gained new insights into the density and structure of matter in the Universe. Several years ago, Hildebrandt had already been involved in a research consortium that had pointed out discrepancies in the data between different groups. The values determined for matter density and structure differed depending on the measurement method. A new analysis, which included additional infrared data, made the differences stand out even more. They could indicate that this is the flaw in the Standard Model of Cosmology.

Rubin, the science magazine of Ruhr-Universität Bochum, has published a report on Hendrik Hildebrandt’s research. The latest analysis of the research consortium, called Kilo-Degree Survey, was published in the journal Astronomy and Astrophysics in January 2020.

Two methods for determining the structure of matter

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

CMB per ESA/Planck


ESA/Planck 2009 to 2013

The Kilo-Degree Survey team, as well as several other groups, determined the density and structure of matter using the gravitational lensing effect: as high-mass objects deflect light from galaxies, these galaxies appear in a distorted form in a different location than they actually are when viewed from Earth.

Gravitational Lensing

Gravitational Lensing NASA/ESA

Based on these distortions, cosmologists can deduce the mass of the deflecting objects and thus the total mass of the Universe. In order to do so, however, they need to know the distances between the light source, the deflecting object and the observer, among other things. The researchers determine these distances with the help of redshift, which means that the light of distant galaxies arrives on Earth shifted into the red range.

New calibration using infrared data

To determine distances, cosmologists therefore take images of galaxies at different wavelengths, for example one in the blue, one in the green and one in the red range; they then determine the brightness of the galaxies in the individual images. Hendrik Hildebrandt and his team also include several images from the infrared range in order to determine the distance more precisely.

Previous analyses had already shown that the microwave background data from the Planck Consortium systematically deviate from the gravitational lensing effect data. Depending on the data set, the deviation was more or less pronounced; it was most pronounced in the Kilo-Degree Survey. “Our data set is the only one based on the gravitational lensing effect and calibrated with additional infrared data,” says Hendrik Hildebrandt, Heisenberg professor and head of the RUB research group Observational Cosmology in Bochum. “This could be the reason for the greater deviation from the Planck data.”

To verify this discrepancy, the group evaluated the data set of another research consortium, the Dark Energy Survey, using a similar calibration. As a result, these values also deviated even more strongly from the Planck values.

Dark Energy Survey


Dark Energy Camera [DECam], built at FNAL


NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

Timeline of the Inflationary Universe WMAP

The Dark Energy Survey (DES) is an international, collaborative effort to map hundreds of millions of galaxies, detect thousands of supernovae, and find patterns of cosmic structure that will reveal the nature of the mysterious dark energy that is accelerating the expansion of our Universe. DES began searching the Southern skies on August 31, 2013.

Debate in expert 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 comprehensive data set that could provide further insights. It is expected to provide even more precise data on matter density and structure in spring 2020.

Depending on the data set, the deviation was more or less pronounced; it was most pronounced in the Kilo-Degree Survey. “Our data set is the only one based on the gravitational lensing effect and calibrated with additional infrared data,” says Hendrik Hildebrandt, Heisenberg professor and head of the RUB research group Observational Cosmology in Bochum. “This could be the reason for the greater deviation from the Planck data.”

To verify this discrepancy, the group evaluated the data set of another research consortium, the Dark Energy Survey, using a similar calibration.

According to Einstein’s theory of General Relativity, gravity should lead to a slowing of the cosmic expansion. Yet, in 1998, two teams of astronomers studying distant supernovae made the remarkable discovery that the expansion of the universe is speeding up. To explain cosmic acceleration, cosmologists are faced with two possibilities: either 70% of the universe exists in an exotic form, now called dark energy, that exhibits a gravitational force opposite to the attractive gravity of ordinary matter, or General Relativity must be replaced by a new theory of gravity on cosmic scales.

DES is designed to probe the origin of the accelerating universe and help uncover the nature of dark energy by measuring the 14-billion-year history of cosmic expansion with high precision. More than 400 scientists from over 25 institutions in the United States, Spain, the United Kingdom, Brazil, Germany, Switzerland, and Australia are working on the project. The collaboration built and is using an extremely sensitive 570-Megapixel digital camera, DECam, mounted on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory, high in the Chilean Andes, to carry out the project.

Over six years (2013-2019), the DES collaboration used 758 nights of observation to carry out a deep, wide-area survey to record information from 300 million galaxies that are billions of light-years from Earth. The survey imaged 5000 square degrees of the southern sky in five optical filters to obtain detailed information about each galaxy. A fraction of the survey time is used to observe smaller patches of sky roughly once a week to discover and study thousands of supernovae and other astrophysical transients.

As a result, these values also deviated even more strongly from the Planck values.

Debate in expert 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 comprehensive data set that could provide further insights. It is expected to provide even more precise data on matter density and structure in spring 2020.

See the full article here .

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The Ruhr-University Bochum is one of the largest universities in Germany and part of the Deutsche Forschungsgemeinschaft, the most important German research funding organization.[9]

The RUB was very successful in the Excellence Initiative of the German Federal and State Governments (2007), a competition between Germany’s most prestigious universities. It was one of the few institutions left competing for the title of an “elite university”, but did not succeed in the last round of the competition. There are currently nine universities in Germany that hold this title.

The University of Bochum was one of the first universities in Germany to introduce international bachelor’s and master’s degrees, which replaced the traditional German Diplom and Magister. Except for a few special cases (for example in Law) these degrees are offered by all faculties of the Ruhr-University. Currently, the university offers a total of 184 different study programs from all academic fields represented at the university.[10]