Research Highlights

On this page you can find a monthly updated list of short articles highlighting current MPA research topics.

Current Research Highlights

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The Hydrangea project: high-resolution hydrodynamic simulations of galaxy clusters

January 01, 2017
Why do galaxies that live in the enormous structures known as galaxy clusters look different from normal, isolated galaxies, such as our Milky Way? To answer this question, an international research team led by MPA has created the Hydrangea simulations, a suite of 24 high-resolution cosmological hydrodynamic simulations of galaxy clusters. Containing over 20,000 cluster galaxies in unprecedented detail and accuracy, these simulations provide astrophysicists with a powerful tool to understand how galaxies have formed and evolved in one of the most extreme environments of our Universe. [more]
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The embarrassment of false predictions -
How to best communicate probabilities?

December 01, 2016
Complex predictions such as election forecasts or the weather reports often have to be simplified before communication. But how should one best simplify these predictions without facing embarrassment? In astronomical data analysis, researchers are also confronted with the problem of simplifying probabilities. Two researchers at the Max Planck Institute for Astrophysics now show that there is only one mathematically correct way to measure how embarrassing a simplified prediction can be. According to this, the recipient of a prediction should be deprived of the smallest possible amount of information. [more]
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Studying diffuse, warm gas in the outskirts of galaxies

November 01, 2016
The diffuse gas around galaxies is hard to detect, but shows properties which are quite different to the star-forming gas inside a galaxy. Scientists at MPA have used observations from the recent MaNGA survey to study how the ionized gas changes with distance from the center of the galaxy. They have demonstrated the usefulness of adding spectra from multiple galaxies in order to analyze the gas in the outskirts of galaxies. Their study shows that the brightness of the gas decreases, while its temperature increases the further the gas is located from the center of the galaxy. The differences between star-forming and circumgalactic gas also seem to correlate with the star-formation rate and stellar mass of the galaxies. [more]
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Warps and waves in fully cosmological models of galactic discs

October 01, 2016
The stellar discs of nearby spiral galaxies are generally not flat and often show waves and warps. Even our own Galactic disc seems to be corrugated. It is still not clear what causes these structures. A research team at MPA, together with external collaborators, have revisited this question by analyzing new simulations of spiral galaxy formation. Their study shows that close encounters with satellite galaxies and more distant flybys of massive companions are the most common drivers. However, in some cases, bending patterns in discs can also be driven by the accretion of cold gas. The vertical motions produced by these patterns can be as large as 60 km/s. Such perturbations should be easily detectable in line-of-sight velocity fields of nearly face-on galaxies. This provides a new way to study the structure of galactic stellar discs, allowing us to understand how and how often such corrugation patterns arise in the nearby universe. [more]
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At the edge of galaxy clusters: splashback and accretion shock

September 01, 2016
Observations are beginning to be sensitive enough to see the outskirts of galaxy clusters, where theory predicts interesting features in the dark matter and gas profiles: the so-called splashback and the accretion shock. Scientists at MPA use an analytical model to compute the locations of these features, and shed new light on the underlying physics. [more]
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Thermal conduction in galaxy clusters

August 01, 2016
From X-ray and SZ observations we know all major characteristics of the hot intracluster medium (ICM) filling the entire volume of galaxy clusters - the largest virialized objects in our Universe. However, several important properties are still poorly known, including thermal conduction in the ICM, mediated by electrons. To explain the sharp temperature gradients in galaxy clusters, it is often proposed that thermal conduction is suppressed both by the topology of magnetic-field lines, which tangle electron trajectories, and by variations of the field strength that can trap electrons. The latter mechanism can be crucially important when the so-called mirror instability generates fluctuations of the magnetic field strength: this kinetic instability is triggered by pressure anisotropies in turbulent plasma. Even if such fluctuations are present on truly microscopic scales, they have the potential to completely shut down heat conduction. Scientists at MPA have investigated such a possibility by analysing the results of recent simulations and found that the suppression of thermal conductivity is in fact rather modest, a factor of ~5 compared to unmagnetized plasma. The effect operates in addition to other suppression mechanisms and independently of them, and depends only weakly on the macroscopic parameters of the intracluster medium. [more]
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Predicting the Sunyaev-Zeldovich signal from cosmological, hydro-dynamical simulations

July 01, 2016
Using recent, extensive cosmological simulations, researchers at the Max Planck Institute for Astrophysics have shown that the expected signal from the Sunyaev-Zeldovich (SZ) effect of galaxy clusters on the Cosmic Microwave Background agrees remarkably well with observations by the Planck satellite. However, only a small fraction of this predicted signal is currently observable. The scientists developed a simple analytical model to understand the SZ probability distribution function, which is also helpful in interpreting the observed distribution of galaxy clusters masses. [more]
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