Highlights 2021

In the interstellar medium (ISM) of galaxies, stars form in small groups groups of a few hundred and clusters up to several million stars. A full theoretical model of this process and its impact on galaxy evolution is still in its infancy. MPA researches and their collaborators have developed a highly complex numerical model to simulate the multi-phase ISM and how star clusters emerge in dwarf galaxies. The supercomputer simulations show that the properties of the star clusters depend on how efficiently stars can form from the cold dense gas. Detailed post-processing then allowed the researchers to compare their results to observations. This demonstrates the scientific fidelity of the new model, its current limitations, and observational limitations on how well clusters can be detected in regions of high star formation activity. The studies are a major step towards a comprehensive model for star cluster formation. more

The colours and star formation rates of galaxies are strongly correlated with each other out to distances as large as 10 Megaparsecs. However, current galaxy formation models fail to reproduce these large-scale correlations accurately. Scientists from MPA, the University of Surrey, and Heidelberg University are in the process of updating the Munich galaxy formation model, L-GALAXIES, with a sophisticated and accurate method to model environmental effects for all galaxies. The most recent updated model is in significantly better agreement with observations than its predecessors and exhibits a stronger environmental dependency of galaxy properties out to several Megaparsecs from the centers of their dark matter haloes. more

Approximately 13 billion years ago, the radiation produced by the first galaxies completely transformed the Universe. The vast amount of hydrogen filling the space between galaxies was  ionized in a process called cosmic reionization. Despite their intimate connection, the formation of the first galaxies and the reionization process are typically studied separately. An international team led by and including MPA researchers has now produced the first suite of simulations designed to simultaneously investigate these two processes during the infancy of the Universe, unveiling features of their connection. This new numerical effort – soon to be released publicly – provides a unique platform for investigating the young Universe and to fully exploit the forthcoming James Webb Space Telescope. The first results from THESAN have already shown that its unique combination of physical accuracy and simulated scales allows to reproduce most of the available data, including some that escaped previous numerical efforts. more

Cosmological simulations show that the growth of galaxies in the early Universe is regulated by the interplay between gas accretion onto dark-matter halos and ejection of matter by stars and active galactic nuclei (AGN). While these processes are routinely described in theoretical works, still little is known from observations on the complex exchanges of mass and energy within the halos of galaxies, where large-scale infall (i.e. accretion) meets outflows (i.e. ejection). Recently, an international team of astronomers was able to probe the halo gas of a massive galaxy system, SMM J02399-0136, using a novel approach. These observations unveiled – for the first time – the infall towards the galaxies of a large mass of diffuse, highly turbulent multiphase gas, pervaded by powerful outflows and more than 10 times larger than the star-forming galaxies. more

Astronomers have made the rare sighting of two stars spiralling to their doom by spotting the tell-tale signs of a teardrop-shaped star. The tragic shape is caused by a massive nearby white dwarf distorting the star with its intense gravity, which will also be the catalyst for an eventual supernova that will consume both. more

The gas in and around galaxies can be probed with absorption line studies using light from background quasars. Scientists at MPA have now used a large sample from the SDSS DR16 to automatically detect absorbers in background quasars and connect them with foreground galaxies. Their analysis shows that cool circumgalactic gas has a different physical origin for star-forming versus quiescent galaxies. more

Some of the most energetic radiation that reaches Earth comes from an exploded star in our Galaxy. An international team of researchers was now able to measure the distance to this object using an adjacent dust cloud with much higher degree of precision than ever before. This is the first step in better understanding the energetic processes that are going on in this supernova remnant. more

Magnetic fields are ubiquitous in the Universe today, from stars to clusters of galaxies. Their origin, however, remains a mystery. MPA researchers have now simulated in great detail a variety of proposed mechanisms for magnetogenesis – i.e. how magnetic fields might be created – in high-redshift galaxies. They also studied their impact on the formation and evolution of galaxies, providing guidance to both future observations and simulations. Their work demonstrates that high-redshift galaxies may hold the key to understanding the origin of cosmic magnetic fields. It also provides the first-ever investigation on galactic scales of a novel magnetogenesis mechanism. more

Intermediate mass black holes (IMBH) should be linking observed stellar black holes and supermassive black holes, but their formation mechanisms are still debated. Young and dense massive star clusters are promising environments for the formation of such black holes through collisions. An international team lead by MPA researchers has presented novel realistic simulations of star clusters, where these missing links form by rapid collisions of stars and black holes. The study also predicts an IMBH formation channel by the merging of black holes in a mass regime, which is excluded by stellar evolution models. In this “mass gap” a black hole merger has indeed been observed recently by the LIGO/Virgo gravitational wave collaboration. more

Where are the baryons? This question naturally arises as the predicted abundance of baryons in the universe - the basic building blocks of all elements in the periodic table – do not agree with observations of the intergalactic medium. Locating the missing baryons will help us to not only better understand the formation and evolution of galaxies, but also to better constrain possible extensions of the current standard model of cosmology. MPA researchers have turned to a novel approach in modelling the galaxy distribution to optimize measurements of the kinematic Sunyaev-Zel'dovich effect, an emerging tool to probe the distribution of baryons in galaxy clusters. more

How can machine learning methods help us understand our tangled cosmic web? A new study presents a ‘deep learning’ framework to shed light onto the physics of the formation of dark matter halos. The results show that spherical averages over the initial conditions of the Universe carry the most relevant information about the final mass of halos. more

Radio telescopes observe the sky in a very indirect fashion. Sky images in the radio frequency range therefore have to be computed using sophisticated algorithms. Scientists at the MPI for Astrophysics have developed a series of improvements for these algorithms, which help to improve the telescopes' resolution considerably. more