Stellar News

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

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

Observations of a newly discovered binary star system combined with advanced models of stellar collapse have provided key insights into the formation of stellar mass black holes. A team of international researchers at the Max Planck Institute for Astrophysics and the Niels Bohr Institute (NBI), University of Copenhagen, conclude that massive black holes can form without a bright supernova explosion. The energy from the collapse is carried away mainly by lightweight neutrino particles with only small asymmetry, leading to a small natal kick for the black hole. more

Betelgeuse is a well-known red supergiant star in the constellation Orion. Recently it has gained a lot of attention, not only because variations in its brightness led  to speculations that  an explosion might be imminent, but also because observations indicated that it’s rotating much faster than expected. This latter interpretation is now put into question by an international team led by astronomers at Max Planck Institute for Astrophysics, who propose that Betelgeuse’s boiling surface can be mistaken for rotation even in the most advanced telescopes. Other astronomers are actively analyzing new observational data to test such hypotheses. more

In dense stellar environments, interactions between stars and stellar-mass black holes should occur frequently. Through hydrodynamical simulations, researchers at MPA have explored how stars are disrupted in such encounters, varying key parameters such as stellar and black hole masses, stellar age, and approach distance. The study quantifies the impact of these initial parameters on stellar remnants' masses, spins, and trajectories, offering insights into cluster dynamics and providing best-fit formulae for post-disruption parameters. more