Stellar News

In January, Prof. Dr. Tobias Bonhoeffer, Advisor to the MPG President on Africa Affairs, visited the Partner Group of the Max Planck Institute for Astrophysics at Kyambogo University in Uganda, led by Dr. Benard Nsamba. Prof. Bonhoeffer met with the university's top management and participated in a productive collaborative board meeting, discussing future research initiatives and opportunities for deeper cooperation.
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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

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

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.
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Computer simulations suggest that the amplification of magnetic fields in stellar collisions may play an important role in the formation of a particular subset of stars in clusters. Blue straggler stars in clusters appear not only bluer, but also younger than other cluster members. One proposed explanation for their apparently different ages is that they are the result of stellar collisions. However, this would require the resulting star to spin down efficiently without losing too much mass. Scientists at the Max Planck Institute for Astrophysics have now shown, using sophisticated 3D simulations, that the energy of the magnetic field is greatly amplified in the collisions of low-mass stars, providing a potentially efficient spin-down mechanism. 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

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