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COSMOLOGY

How much does the Universe weigh?

New results from physicists in Bochum have challenged the Standard Model of Cosmology.
“Since time immemorial people have been looking at the sky and trying to understand how much stars, planets, galaxies and other objects weigh,” says Professor Hendrik Hildebrandt, Heisenberg professor and head of the RUB research group Observational Cosmology. He and his team are investigating this question. More precisely, the group is not only interested in how much mass is present in the Universe, but also in its structure, i.e. whether the mass is evenly distributed in space or whether it occurs in lumps.

In order to weigh objects in the sky, cosmologists use the so-called gravitational lensing effect. When the light rays emitted by a galaxy pass massive objects on their way to Earth, they are deflected by the gravity of these objects. The heavier the object, the greater the deflection of the light beam. A galaxy whose light is deflected by the gravitational lensing effect therefore appears from Earth in a different place than it actually is. If researchers could measure the deflection, they could deduce its weight. But in order to do so, they have to overcome quite a few obstacles.

Difficulties in determining mass

“We only see the galaxy at its shifted location, but we do not know where it actually is,” as Hendrik Hildebrandt outlines one of the problems. In addition, researchers need to know the distances between the light-emitting galaxy, the deflecting mass and the observer in order to calculate the mass. “But as we only ever see a two-dimensional image of the sky, it is difficult to estimate how far away objects are along the line-of-sight,” elaborates the physicist.

Still, researchers have developed tools to address these problems. They take advantage of the fact that the massive objects do not deflect the light like perfect lenses, but create distortions. The image of a galaxy then appears as if it was viewed through the foot of a wine glass.

Gravitational lensing

Researchers can calculate these distortions; they determine the deviation from the original shape of the galaxy – naturally, they have to know its original shape in order to do so.

Average over millions of galaxies

Typically, this can’t be done for individual objects. However, researchers know what galaxies are supposed to look like on average. They therefore average over a large number of galaxies and calculate their average distortion, also known as shear. Using statistical methods, the research team determines the distortion of tens of millions of galaxies for large sections of the sky. Based on these results, the physicists can then reconstruct the deflections of light and thus the mass of the deflecting objects – provided they know the three-dimensional distances of the objects from each other.

In order to determine the density of matter in the universe using the gravitational lensing effect, cosmologists look at distant galaxies, which usually appear in the shape of an ellipse. These ellipses are randomly oriented in the sky.
In order to determine the distance of objects, the researchers use the colour of the galaxies. It has long been known that light from more distant galaxies shifts to the red as it arrives on Earth. The colour of a galaxy can thus be used to determine its distance. Cosmologists take images of galaxies at different wavelengths, for example one in the blue, one in the green, one in the red and possibly several in the infrared range. They subsequently determine the respective brightness of the galaxy in the different images. This method has long been established. “It works particularly well when you include data from the infrared range,” says Hendrik Hildebrandt, who is an expert in this type of analysis and who has introduced precisely this expertise to a project called the “Kilo-Degree Survey” – which caused quite a stir in the cosmological community.

© Roberto Schirdewahn

Based on the data compiled in the Kilo-Degree Survey, the research consortium determined a combined value for the density and the clumping tendency of matter in the Universe. “So far, we have been unable to distinguish clearly whether there is a lot of matter that is evenly distributed in the Universe or little matter that is extremely lumpy,” admits Hildebrandt. In the end, the analysis does not yield a single value, but rather a possible range of values into which matter density and clumping tendency might fall.

Second method for measuring the density of matter

However, scientists can measure these parameters not only with the gravitational lensing effect, as the research consortium with Hendrik Hildebrandt has done, but also with another method based on the cosmic microwave background. This refers to radiation in the microwave range, which was emitted shortly after the Big Bang and can still be measured today.

Today, values for matter density and lumpiness are available from several research consortia that used the gravitational lensing effect, as well as data from the Planck Consortium that used the cosmic microwave background. But the results do not match. Rather, the gravitational lensing measurements seem to deviate systematically from the microwave background measurements; the most obvious deviation is between the Planck Consortium and the Kilo-Degree Survey, in which Hendrik Hildebrandt is a major contributor. “There can be several reasons for this outcome,” he points out. “Either we or one of the other research consortia has made a systematic error in data evaluation – or there is something wrong with the Standard Model of Cosmology.”

This fundamental model of cosmology, based on Einstein’s general theory of relativity, describes the origin and evolution of the Universe. Researchers need it to interpret their data. “We have also included alternative models for interpretation and have actually found one that reconciles our data with those of the microwave background measurements,” says the physicist.

Standard Model of Cosmology might be wrong

In the alternative model, Einstein’s cosmological constant, which describes the gravitational force, is replaced by the so-called dark energy – a force responsible for the accelerated expansion of the Universe. “What’s interesting about the alternative model is that the dark energy in it changes over time,” explains Hendrik Hildebrandt. This could explain the discrepancy between the data sets. This is because the cosmic microwave background originates from the young Universe shortly after the Big Bang; the gravitational lensing effect, on the other hand, measures a much older Universe – the dark energy could have changed during this time span.

More extensive analysis in progress

According to Hildebrandt, it is too early yet to reject the Standard Model of Cosmology. Statistically, there is an approximately one-percent probability that the Kilo-Degree Survey data set will overlap with the Planck data. Hendrik Hildebrandt and his cooperation partners therefore intend to determine the density and lumpiness of matter even more precisely than before and are currently evaluating a more comprehensive data set. “It remains to be seen whether, after this analysis, our data will be even less compatible with the Planck Consortium’s data or whether they can both be reconciled,” he says.

Either way, this is a pivotal moment for the Bochum-based researcher. “It is the first time in my research career that I have reached such a critical point,” he stresses. “The noblest task of an experimental physicist is to bring down theories.” Now the Bochum-based team is eagerly waiting to see whether the explanation for the discrepancy in the data will be a quite mundane one, namely a measurement error. “But it is quite possible that we will trigger a revolution with our new data,” concludes Hildebrandt. The team expects the results to be released in late spring 2020.

The Very Large Telescope (in the background) is located on Paranal in northern Chile in the Atacama Desert, which offers optimal conditions for astronomical observations. In the foreground is the Vista telescope that supplies the infrared data.

written by Julia Weiler, RUB
Plasma biology

Plasma-driven biocatalysis 

©RUB, Marquard

A research team from Bochum has developed a new method to drive catalytically active enzymes.

Compared with traditional chemical methods, enzyme catalysis has numerous advantages. But it also has weaknesses. Some enzymes are not very stable. Enzymes that convert hydrogen peroxide are even inactivated by high concentrations of the substrate. A research team at Ruhr-Universität Bochum (RUB), together with international partners, has developed a process in which the starting material, i.e. hydrogen peroxide, is fed to the biocatalysts in a controlled manner using plasma. The enzymes themselves are protected from harmful components of the plasma by a buffer layer. Using two model enzymes, the team showed that the process works, as reported in the journal “ChemSusChem” from 5 February 2020.

Milder conditions, less energy consumption and waste

In biocatalysis, chemicals are produced by cells or their components, in particular by enzymes. Biocatalysis has many advantages over traditional chemical processes: the reaction conditions are usually much milder, energy consumption is lower and less toxic waste is produced. The high specificity of enzymes also means that fewer side reactions occur. Moreover, some fine chemicals can only be synthesised by biocatalysis.

The weak spot of enzyme biocatalysis is the low stability of some enzymes. “Since the enzyme often has to be replaced in such cases – which is expensive – it is extremely important to increase the stability under production conditions,” explains lead author Abdulkadir Yayci from the Chair of Applied Microbiology headed by Professor Julia Bandow.

Hydrogen peroxide: necessary, but harmful

The research team has been studying two similar classes of enzymes: peroxidases and peroxygenases. Both use hydrogen peroxide as a starting material for oxidations. The crucial problem is that hydrogen peroxide is absolutely necessary for activity, but in higher concentrations it leads to a loss of activity of the enzymes. As far as these enzyme classes are concerned, it is therefore vital to supply hydrogen peroxide in precise doses.

To this end, the researchers investigated plasmas as a source of hydrogen peroxide. Plasma describes the fourth state of matter that is created when energy is added to a gas. If liquids are treated with plasmas, a large number of reactive oxygen and nitrogen species are formed, some of which then react to form long-lived hydrogen peroxide, which can be used for biocatalysis.

Biocatalytic reactions with plasma-generated hydrogen peroxide are possible

In an experiment in which horseradish peroxidase served as one of the model enzymes, the team showed that this system works in principle. At the same time, the researchers identified the weak points of plasma treatment: “Plasma treatment also directly attacks and inactivates the enzymes, most likely through the highly reactive, short-lived species in the plasma-treated liquid,” outlines Abdulkadir Yayci. The research group improved the reaction conditions by binding the enzyme to an inert carrier material. This creates a buffer zone above the enzyme in which the highly reactive plasma species can react without harming the enzyme.

The researchers then tested their approach using a second enzyme, the unspecific peroxygenase from the fungus Agrocybe aegerita. This peroxygenase has the ability to oxidise a large number of substrates in a highly selective way. “We successfully demonstrated that this specificity is maintained even under plasma treatment and that highly selective biocatalytic reactions are possible using plasma,” concludes Julia Bandow.

written by Marike Drießen, RUB

Press release

Public outreach

Plasma workshop at Bo.Ing 2020

The SFB-TR 87 and CRC 1316 joined the workshop program of the Bo.Ing 2020. At the Bochum engineering forum "BO.Ing", pupils are given an insight into the engineering sciences in workshops, laboratory tours and discussion groups. The event is organised by the zdi network IST.Bochum.NRW and is implemented in cooperation with universities from Bochum and the surrounding area.

With plasma workshop, sixteen pupils in two different workshop learned the basic ideas about plasma and its applcation. In hands-on activities, the girls and boys were able to perform their own experiments.

Events

Plasma theory day

Organized under the umbrella of the RAPP Center and Research Department Plasma, we are happy to announce the second Plasma Theory Day at RUB, to take plase from March 16 to March 17, 2020. The program is now online here.

It is meant to further intensify the scientific discussion in the area of plasma- and plasma-astrophysics in the UAR research landscape. Please forward this message to everybody interested. I would appreciate if those who intend to come write an email to me, as I need an estimate concerning the size of the lecture hall. Right now we plan to be in NB7/67, but I can reserve a larger room if necessary.

Upcoming Workshop

7th International Plasma Science & Interfaces Workshop

On November 2 & 3, 2020, the 7th International Plasma Science & Interfaces Workshop takes place at the event centre of the Ruhr-Universität Bochum. The event is organized by Hugo de Haan (programme, Vision Dynamics), Guus Peemen (chair, TuE), and Achim von Keudell (host and chair, RUB).

Key topics and themes:

  • Plasma medicine, medical and healthcare
  • Plasma Surface modification & thin films
  • Atmospheric pressure plasma @ Micro/Nano scale
  • Atmospheric pressure plasma jet (APPJ)
  • Nanoparticles generation and pariclesurface treatment
  • Surface diagnostics, energetics, analytics and –metrology
  • Plasma parameterization, diagnostics, simulation
  • Plasma for Emission Abatement & CO2
  • Plasma parameterization, diagnostics, simulation

The workshop will be a PhD (student) expert-level workshop focused on the achievements, challenges and opportunities for the scientific- and entrepreneurial  community working in the field.