Current Research Highlights

In recent years, a tantalizing hint of new physics was found in polarization data of the cosmic microwave background from the WMAP and Planck space missions. The so called “cosmic birefringence” is violating parity symmetry, however, the validity of the result was questioned, because the analysis method depends on the modeling of Galactic dust emission. Now, the cosmological interpretation of the signal gains strength as MPA scientists find a comparable effect in the newest data release from the Atacama Cosmology Telescope without relying on Galactic emission. If further independent observations confirm this result as a genuine cosmological signal, it would have profound implications for the fundamental laws of physics and shed light on the mysterious nature of dark matter and dark energy. more

More and more black holes are found orbiting a luminous massive stellar companion. The future of these systems holds a fundamental puzzle: once the companion star expands and begins to lose mass onto the black hole, will the interaction remain stable or will the black hole plunge into the star and destroy it from within? Using state-of-the-art computational models, a team led at MPA has identified a surprisingly simple rule: the interaction is stable as long as the distance between the black hole and the star remains larger than about ten times the radius of the Sun. The newly found separation threshold will play a key role in determining which systems survive to form gravitational-wave sources and will help interpret the growing population of LIGO/Virgo/Kagra detections. Binaries that fail to remain stable, however, are no less remarkable. Such black hole-star mergers could be the explanation for luminous fast blue optical transients, linking these rare and powerful explosions to the violent end states of binary evolution. more

The space around galaxies might not glow brightly in telescopes, but it is, in fact, filled with gases at vastly different temperatures. From plasma at a million degrees Celsius to much colder, tiny, cold clouds at temperatures that can be found on Earth. Understanding how these gases interact is key to explaining how galaxies grow, form stars, and evolve. But the vast temperature difference has proved to be a significant challenge for simulations, as it also results in a big difference in densities.  A team of scientists from MPA and AIP (Potsdam) has now developed a new model, MOGLI, that can track these interactions in unprecedented detail. By treating hot and cold gas as two coupled components that exchange material and energy, a multifluid approach, developed in engineering circles for numerous terrestrial applications, allows large cosmological simulations to capture the hidden life of cold gas. more

When two stars orbit close together, one star can transfer material to its companion, dramatically changing both stars' evolution. However, how much of this transferred material actually stays with the receiving star has remained one of the biggest mysteries in binary star physics. Using a new sample of 16 carefully studied binary systems, MPA scientists have now discovered that binary stars are much more efficient at keeping transferred material than previously thought, with many systems retaining more than half of the mass that was donated. This finding challenges decades of theoretical assumptions and has profound implications for our understanding of stellar evolution, affecting everything from the types of supernovae we observe to the formation of gravitational wave sources, X-ray binaries, and exotic stellar objects like blue stragglers. more

Black holes with masses between the stellar and supermassive regime are among the most elusive objects in the Universe. These intermediate-mass black holes are believed to reside in many dwarf galaxies. Using new, high-resolution supercomputer simulations, MPA scientists discovered that nuclear star clusters — compact, massive clusters of stars at the centres of galaxies — may be key to enabling these black holes to grow, thus shedding light on the origins of supermassive black holes. more

Quasars are active supermassive black holes located at the centres of massive galaxies that emit energy levels that far exceed the binding energy of their host galaxies. This substantial amount of energy has the potential to impact the gas within and around the galaxies, thereby influencing their evolution. While the importance of this process is acknowledged, its details are still the subject of significant debate. An international team of researchers led by MPA scientists has now obtained observations of the most extensive sample of hydrogen structures surrounding quasars in the early universe to better understand this feedback process. The data reveal how the gas responds to the energy released by the supermassive black holes over distances of several hundred thousand light years, providing a new way to study the impact of quasars on galaxy evolution. 
  more

Imagine a star not crashing into a supermassive black hole in a fiery explosion, but instead slowly spiraling in, circling closer and closer to its horizon. This is the story of a sub-giant star that is stripped of its hydrogen layer by a black hole companion with a few million solar masses. The left-over helium core is gently drawn in due to strong gravitational wave emission and can be placed so close to the supermassive black hole that it becomes a promising gravitational wave source for the future detector LISA (Laser Interferometer Space Antenna). This scenario has been recently investigated by a team at MPA. more

Galaxies are surrounded by a large reservoir of gas called the circumgalactic medium (CGM), where they refuel and recycle the gas for forming stars and growing in mass. This gas is extremely dim, with current observations being limited to spectral lines that are hard to interpret. It is therefore challenging to understand the mass, distribution, and physical conditions prevalent in the CGM. Recently, a group of researchers at MPA serendipitously discovered bright oxygen emission around a massive galaxy group in the distant universe using the James Webb Space Telescope (JWST). In collaboration with other international scientists and by combining various observations, the study provides a detailed and unprecedented view of the CGM, showing how galaxies influence the gas and their environment. more

Ground-based gravitational wave detectors like LIGO and Virgo have brought significant attention to binary systems composed of black holes and neutron stars as gravitational wave sources. However, two white dwarfs in a binary system are expected to be far more numerous. In particular, the pre-merger phase of double white dwarfs could lead to high-energy astrophysical events that would emit gravitational waves detectable by the European Space Agency’s upcoming Laser Interferometer Space Antenna (LISA) mission. Understanding how these double white dwarfs form is essential to interpreting the future LISA data. For the first time, researchers at the Max Planck Institute for Astrophysics (MPA) have now quantitatively assessed the impact of triple evolution on LISA sources. This study underscores the importance of triple interactions in the formation of double white dwarfs, revealing previously unexplored pathways that contribute to the gravitational-wave sources LISA will observe.
  more

The nature of dark matter is still very much unknown; viable candidates range from microsopic elementary particles to black holes with masses many times that of the Sun. Researchers at MPA, Carnegie Observatories, and the University of Sussex have recently made concrete and reliable predictions for how the Universe would look if dark matter consists entirely of massive black holes: they performed the first self-consistent study of how structure would form in such a Universe, and how many of these black holes merge and emit observable gravitational waves. more

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