Current Research Highlights

The expansion rate of the Universe, quantified by the Hubble constant (H₀), remains one of the most debated quantities in cosmology. Measurements based on nearby objects yield a higher value than those inferred from observations of the early Universe—a discrepancy known as the "Hubble tension". Researchers at the Max Planck Institute for Astrophysics and their collaborators have now presented a new, independent determination of H₀ using Type II supernovae. By modeling the light from these exploding stars with advanced radiation transport techniques, they were able to directly measure distances without relying on the traditional distance ladder. The resulting H₀ value agrees with other local measurements and adds to the growing body of evidence for the Hubble tension, offering an important cross-check and a promising path toward resolving this cosmic puzzle. more

Most stars form in clusters, deeply embedded in the densest and coldest cores of giant molecular gas clouds. A few million years into the formation of a cluster the remaining gas is finally expelled by supernova explosions. Thereafter the clusters lose stars in the galactic tidal field and eventually disrupt. This entire life-cycle is very difficult to observe. Star clusters begin their lives deeply embedded in their birth clouds and are invisible to most observatories and the disruption of a single cluster can take tens of millions of years or more. An international team led by researchers at MPA has presented a new high-resolution supercomputer simulation, which can follow entire galactic star cluster life-cycles from birth to disruption and sheds light on the unobservable phases of star cluster evolution. more

The formation and evolution of galaxies are among the most complex challenges in astrophysics. Recent advancements with instruments like JWST and ALMA have shed light on high-redshift galaxies – those that existed billions of years ago. However, most theoretical models are tuned to match galaxies in the local universe. Researchers from the Max Planck Institute for Astrophysics and the University of Bonn now comprehensively evaluated the Munich semi-analytical model L-GALAXIES using the latest observations and found that while the model aligns well with the properties of local galaxies, it struggles with key aspects of high-redshift galaxies. Particularly, the study highlights critical issues with the model’s predictions of quenched galaxies, those that have ceased star formation. Their results suggest a need to revise the implementation of processes driving star formation quenching, including supermassive black hole feedback and galaxy mergers.
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The distribution of matter in the universe is predicted by supercomputer simulations to occur in a network of filaments, known as the "cosmic web", where galaxies form and evolve. The vast majority of this intricate structure is in the form of diffuse hydrogen gas, so rarefied that it is extremely challenging to observe it directly. A collaboration led by MPA researchers has targeted the active supermassive black holes of galaxy pairs at close separations to reveal the connecting filamentary structures of the cosmic web in the early universe. The results are promising and unveil evidence for such structures stretching between the observed pairs, ultimately providing excellent targets for future ultra-deep observations. more

Galaxies are not islands in the cosmos. While globally the universe expands – driven by the mysterious ‘dark energy’ – locally, galaxies cluster through gravitational interactions, forming the cosmic web held together by dark matter’s gravity. For cosmologists, galaxies are test particles to study gravity, dark matter and dark energy. For the first time, MPA researchers and alumni have now used a novel method that fully exploits all information in galaxy maps and applied it to simulated but realistic datasets. Their study demonstrates that this new method will provide a much more stringent test of the cosmological standard model, and has the potential to shed new light on gravity and the dark universe. more

New observations by the James Webb Space Telescope (JWST) have revealed that supermassive black holes (SMBHs) of more than one million solar masses were already present only 450 million years after the Big Bang. How did these first SMBHs form? A team of researchers at MPA has used modern supercomputer simulations to show that progenitors of SMBHs (seeds) of a few thousand solar masses can form rapidly in dense and structured star clusters forming in the early Universe. They emerge from collisions of massive stars which form supermassive stars and then collapse directly into black holes, which can further grow by merging with other black holes. This new and more realistic model resembles JWST observations and can explain the formation of SMBH seeds which are massive enough to further grow into the earliest SMBHs observed. For this SMBH seed formation process, the researchers predict a unique gravitational wave fingerprint from black hole merger that can be directly tested with the next-generation gravitational wave observatories. more

The groundbreaking detections of gravitational waves from merging pairs of black holes have left us with an intriguing question: how do black holes get close enough to merge? Scientists at MPA show that some of them may have started out as massive stars orbiting one another at extremely large separations — 1,000 to 10,000 times the distance between Earth and Sun. Once these stars end their lives and form black holes, the gravity of the entire galaxy in which they reside could slowly deform the shape of their orbit leading to a close encounter and merger of the black holes. more

Among many X-ray sources in our Galaxy, the one called SS 433 (as an entry number 433 in the catalog of Halpha emitters by Stephenson & Sanduleak 1977) is especially famous and peculiar.  It is likely powered by a black hole in a massive binary system. The accretion rate on this black hole from its companion star is hundreds of times higher than the critical value known as the Eddington limit (when the pressure of produced radiation becomes so great that it can eject matter and form powerful “winds” of the accretion disk). The new model discusses the impact of such winds on the surrounding interstellar medium. In particular, this wind can inflate the giant W50 nebula, encompassing SS 433 and spanning tens of parsecs in size. A similar situation may occur for rapidly growing massive black holes at the dawn of the Universe, galaxies with extreme nucleus activity and star formation rates during the “Cosmic Noon” (when the Universe was about 2-3 billion years old), or in the most extreme ultraluminous X-ray sources in normal star-forming galaxies today. more

With the recent advancements in the Lyman-alpha observations, it becomes more and more important to have theoretical models to help us decode the intricate Lyman-alpha spectral line. Scientists at MPA developed a theoretical approach to describe the escape of Lyman-alpha from scenarios where there is an empty hole to emulate the porous gas around galaxies. more

Can machine learning make new discoveries in astrophysics? An ‘explainable’ neural network is employed to get insights into the origin of dark matter halo density profiles. The network discovers that the shape of the profile in the halo outskirts is described by a single parameter related to the most recent accretion of mass. This is done without prior knowledge of the halo’s evolution history being provided during training.
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A careful analysis of the filaments in the cosmic large-scale structure has revealed interesting new findings about the evolution and complexities of the cosmic web. While some filaments show a significant evolution – depending on their cosmic environment – global filament properties are preserved, which could be used in future cosmological studies. The MPA team also developed a new method to allow for rigorous calibration of the filament catalogues.
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The distribution of galaxies on large, cosmological scales holds important clues on the nature of dark matter, the properties of dark energy and the origin of our Universe. Yet, optimally retrieving this information from observations is challenging. MPA researchers are developing a novel analysis approach, where they follow the evolution of cosmic structures through their entire formation history. Enabling a very detailed comparison between theoretical models and observational data, this approach will allow measuring key parameters of dark matter and dark energy very precisely. more