MPG Yearbook Articles Written by MPE Members

Supernova remnants are what is left after a star explodes: a good part of their emission happens in radio and in X-rays. Here we present the analysis of Vela Jr, carried out with the X-ray all-sky survey dataset provided by the MPE-led mission eROSITA. This dataset allows to image the entire remnant for the first time after the ROSAT mission launched in 1990. We find the spectrum of Vela Jr is featureless and we provide a new measurement for the geometric center. We investigate also the NW rim of the remnant, where particle acceleration is supposed to take place, a process still poorly known.

The discovery of the massive black hole in the center of the Milky Way was honored in 2020 with the Nobel prize. Yet, our research nowadays goes way beyond the discovery. We don’t ask anymore whether the black hole exists, rather we use it to conduct physics experiments in the sky. It is perfect laboratory, located at a mere 26.000 light years in our cosmic backyard. This allows for breath-taking precision measurements that not only test Einstein’s theory of general relativity, but that even reveal that beyond the black hole, not much more matter can hide in the Milky Way center.

For the first time, we have observed a conveyor belt from the outskirts of a star-forming dense cloud directly depositing material near a pair of young forming stars. The gas motions in the conveyor belt, dubbed a 'streamer', mainly obey the gravitational pull from the innermost part of the core. The streamer delivers a large amount of gas with chemicals recently produced in the larger mother cloud directly to the young protostars. These results are striking evidence that the large-scale environment around forming stars has an important influence on small-scale disk formation and evolution.

Which galaxies harbour the most massive black holes? Even though galaxies tend to get more luminous towards their centres, the most massive galaxies exhibit a deficit of stars in their centres. The giant galaxy Holm 15A exhibits a particularly large deficit, and in this galaxy, we found a 40-billion-solar-mass black hole – the most massive known today. The faint centres of giant galaxies thus are an important indicator for the mass of their black hole – potentially even at distances, where direct measurements are not possible today.

Spectrum-Roentgen-Gamma (SRG) is a bilateral space mission of Russia and Germany with the German contribution of the primary payload, the X-ray telescope eROSITA. eROSITA will systematically scan the entire sky for four years with unprecedented sensitivity. The primary science goal is the determination of the large scale structure of the universe and how these structures evolved over cosmic times. This could aid to unlock the secrets of the enigmatic Dark Energy which drives the universe apart. The first scientific results confirm our confidence to reach the mission goals.

A century after the advent of the theory of general relativity by Albert Einstein, we are witnessing an outstanding year 2018 in black hole research. In three ground-breaking measurements with the MPE-led GRAVITY experiment, we could for the first time directly prove the gravitational redshift from a massive black hole, follow the orbital motion of accreting matter very close to the point of no return, and weigh the mass of black holes more than a billion light years away. With its unique image sharpness and sensitivity, GRAVITY is revolutionizing observational astronomy.

For a long time the formation of protostellar disks – a prerequisite to the formation of planetary system around stars – was considered to be difficult. The magnetic field threading the dense rotating molecular cloud is dragged to the center by the gravitational collapse, resulting in a braking effect that carries away angular momentum from the central region. Hardly any rotationally supported disk can form this way, unless the tiny grains are removed from the cloud and the separation between the magnetic field and the collapsing flow is enhanced.

The rich diversity of galaxy morphologies grows out of complex physical processes that govern the formation of new stars and the assembly of stellar mass over time. The advent of new near-infrared facilities allowed us to extensively study the distribution of stellar types and chemical properties of distant massive galaxies by measuring the absorption features in their spectra. This constrained their formation times and provided a more detailed picture of their stellar mass distribution, and their dynamical state at the time when the Universe was less than 4 billion years old.

The Milky Way is a barred spiral galaxy whose central part, the rotating bulge, must have mostly formed from the Galactic disk. With new infrared data the spatial structure of the Galactic bar and bulge could be determined for the first time. This makes it possible to predict the orbits of stars in the inner Galaxy and to link these with their chemical properties. With dynamical models we investigate the present-day structure and evolutionary history of our Galaxy.

The birth of a Solar-type star and its planetary system, starting from interstellar clouds in our Galaxy, can elucidate the formation of our own Solar System, including the production of complex organic molecules found in comets and meteorites. We are using dynamical models, astrochemical codes and powerful telescopes to study the physical and chemical structure of dense cloud cores, the future stellar cradles. Recently, we made predictions on the detection of glycine, the simplest amino acid, and we started to unveil the first steps toward the formation of protoplanetary disks.

Solar system X-ray research has experienced a boost during the last two decades. Before 1996, Sun, Earth, Moon, and Jupiter were the only solar system X-ray sources known. Since then, this number has considerably increased, including now also Mercury, Venus, Mars, Saturn, the Jovian moons Io and Europa, the Io plasma torus, the rings of Saturn, two asteroids, as well as comets as an unexpected new class, and even the heliosphere itself. This article outlines the sequence of discoveries, describes how the X-ray emissions originate, explains their importance, and concludes with an outlook.

The discovery of the accelerated expansion of the Universe has revolutionized the field of physical cosmology. Understanding the origin of this phenomenon is one of the most outstanding problems in physics today. This situation has led to the construction of a new generation of galaxy surveys, aimed at shedding light on this problem. The ongoing Baryon Oscillation Spectroscopic Survey (BOSS) is an example of these surveys. BOSS is probing the large-scale structure of the Universe with unprecedented precision, providing new insights on the physics behind cosmic acceleration.

The black hole at the the centre of the Milky Way is – given its size – surprisingly quiet, because it is accreting only a small amount of matter currently. This may change in 2013 since a gas cloud is approaching it almost directly. In autumn 2013, the cloud will get too close to survive this fly by. The tidal forces as well as the atmosphere of the black hole will act on the gas cloud. If these interactions sufficiently slow down the gas, it can be accreted. We then may observe the „feeding“ of the black hole.

eROSITA is the core instrument on the Russian Spectrum-Roentgen-Gamma mission. From 2013 on eROSITA is expected to deeply survey the entire X-ray sky. The driving science is the detection of 100.000 distant galaxy clusters in order to study the large scale structure in the Universe and test cosmological models including Dark Energy. In addition, eROSITA will detect about 3 million Active Galaxies, widening our view on the evolution of supermassive black holes. eROSITA will also provide new clues on other astrophysical topics, like X-ray binaries and the diffuse galactic emission.

The MPE successfully performs research on complex plasmas on the International Space Station ISS since ten years. This allows scientifically new insights in many fields of physics. More than 60 publications in refereed journals have appeared. Some results shall be presented here. This research not only has a successful history but also a promising future: the next lab PK-4 shall be launched in 2014 and for the farer future a new lab is under development. Thus, plasma crystal research might cover the whole span of life of the ISS.

The new space telescope Herschel of the European Space Agency ESA, with its MPE-provided instrument PACS on board, enables photometric and spectroscopic observations in the far infrared. Photometric surveys with this facility have now shown that the rapid formation of stars in galaxies in the early Universe took place in a qualitatively different mode than in the more recent past. Furthermore, spectroscopic studies showed, for the first time, in a quantitative way how supermassive black holes in the centers of galaxies could terminate the formation of new stars.

The mean ionic charge of solar energetic particles provides critical information for the determination of the source and the acceleration region of the ions. Gradual events show at energies < 0.5 MeV/amu a mean ionic charge of Q_m ≈ 10 for iron ions, suggesting a solar wind origin and acceleration by coronal or interplanetary shock waves. Impulsive events show a large increase of Q_m(Fe) at 0.1–0.5 MeV/amu from 11 to 20. This can only be explained by acceleration and ionisation in a plasma of sufficiently high density in the low corona, at altitudes of < 0.3 R_S (R_S: solar radius).

The formation and evolution of supermassive black holes is an important area of research at the Max Planck Institute for Extraterrestrial Physics (MPE). A lot of progress was made in the last couple of years using instruments with increasing spatial resolution. The integral-field spectrograph SINFONI built at MPE and now at the Very Large Telescope in Chile is presently the best instrument available to find hidden, inactive black holes in the centres of galaxies. It allows to observe hitherto unstudied galaxy types, yielding important conclusions on the co-evolution of supermassive black holes and their host galaxies.

Elliptical galaxies are surrounded by extended, diffuse stellar halos. In dense galaxy clusters, these halos interact and may be dissolved to form part of the so-called intracluster light. Through Planetary Nebula stars, it has been possible to investigate the kinematics and dynamics in some of these halos, giving new constraints on the formation and on-going evolution of these galaxies.

The hitherto most distant gamma-ray burst (GRB) was recently discovered using the novel 7-channel imager GROND (Gamma-Ray Burst Optical Near-IR Detector), implying the existence of massive stars at an age of the universe of only 800 million years. In addition, GROND delivers unique data concerning the short-time variability of the GRB afterglow which allowed to solve the mystery of the nature of the so-called X-ray flares.

The formation of the large-scale structure of the Universe is essentially determined by the Dark Matter, which constitutes the dominating part of the matter density of the Universe. The visible matter then follows these structures and gives only an indirect picture of the cosmic matter distribution. The COSMOS survey succeeded to provide most detailed picture of the Dark Matter in a sky region with a size of 1.6 square degrees. For the first time the scaffolding of the matter distribution with angular resolution on the sky as well as in depth is seen. It shows a loose network of filaments which intersect in massive structures identified with the locations of galaxy clusters. This overall structure is in good agreement with computer simulations of structure formation models.

Plasmas are regarded as the most disordered state of matter, so it came as a major surprise when in 1994 MPE scientists discovered that under special conditions plasmas can become liquids and may even spontaneously crystallise. These so-called “Complex Plasmas” have unusual properties. They belong to the class of “soft matter” and make it possible, for the first time, to research condensed matter states at the most elementary (individual particle) level at all relevant length and time scales – including the limits and onset of cooperative phenomena.

Using SINFONI, a novel near-infrared imaging spectrometer combined with an adaptive optics system, our SINS survey has discovered rapidly forming and large disk galaxies three billion years after the Big Bang, shedding new light on how galaxies were assembled in the young Universe.

Observations of nearby neutrons stars with the X-ray observatory XMM-Newton revealed a surprising discovery: variations in the X-ray spectrum of RX J0720.4-3125 were found over only a few years. The likely conclusion is that the neutron star precesses. The study of precession may provide an interesting tool to learn more about the inner structure of neutron

Hubble Space Telescope observations reveal that the Andromeda galaxy harbours a central supermassive black hole of 140 million solar masses. The new data exclude astrophysical alternatives to a black hole. The black hole is surrounded by a tiny disk of young stars whose origin remains enigmatic.

With the missions Cluster and Double Star, coordinated measurements in Earth’s magnetosphere with up to 6 spacecraft are now becoming available for the first time. Cluster, with its 4 spacecraft in tetraeder-configuration provides data for variable distances in the range ~100 to 20000 km. These are complimented by the measurements of the Two Double Star spacecraft in polar and equatorial orbit.

The INTEGRAL Gamma-Ray Observatory has provided novel insight into the nature of sources of high-energy radiation. New embedded sources were discovered, because only the high-energy part of radiation can penetrate clouds. Unexpected emission at high energies where thermal emission usually fades was found for sources with extremely high magnetic fields. Together, this leads to a re-evaluation of the relative contributions of source objects and intrinsically-diffuse emission from interstellar space. Such diffuse emission reflects cosmic radiation penetrating the interstellar gas in the Galaxy. High-resolution spectroscopy of diffuse emission addresses mainly two prominent gamma-ray lines: Antimatter annihilates into electromagnetic radiation with a line at 511 keV, and was found to have a surprisingly symmetric spatial distribution in the inner Galaxy; radiactive ²⁶Al decays in the interstellar medium of the Galaxy, emitting a line at 1809 keV; being a by-product of cosmic element synthesis from terminal evolutionary phases of very massive stars, it was ejected into interstellar space, and thus reveals the kinematics of the interstellar gas in such regions, which are hardly accessible through other means.

Osteoporosis is the most frequent disease of the skeletal system. It is defined by reduced (mineral) bone density and changes in the microarchitecture of the bone leading to an increased risk of bone fractures. The measurement of the bone mineral density (BMD) is a well established method in the diagnosis of osteoporosis. But since the fracture risk does not only depend on the bone density, this parameter is only of limited use for assessing the fracture risk. Nowadays it is possible to visualize the complex, three-dimensional (trabecular) bone structures using high resolution imaging techniques (CT and MR). If one compares the morphology of the microarchitecture of the bone with the large scale structure of the galaxies in the universe, one can find similarities: In both cases one deals with filaments and wall-like structures, which enclose empty regions ("voids"). An interdisciplinary research project of the MPE in cooperation with the department of radiology of the TU Munich within the framework of the recently initiated TANDEM-projects has been established. In this project new methods for the quantitative description of complex structures, which were originally developed in the field of astrophysics, are applied to the analysis of three-dimensional images of the trabecular bone structure in order to improve the diagnosis of osteoporosis. The results obtained so far show that the newly developed structure measures are very well suited to predict the mechanical strength of bones in human specimen and the risk of fractures in patients.

INTEGRAL is an ESA space mission to study the sky at hard X-ray and soft gamma-ray energies. Its two main instruments SPI and IBIS cover the energy range 20 keV to 10 MeV, and are mainly devoted to high resolution spectroscopy and fine source imaging, respectively. The observational program started in late December 2002 and concentrated mainly towards the galactic plane, and especially the inner Galaxy. Highlights from the first 15 months of the mission are results on nucleosynthesis and solar flare gamma-ray lines, on a survey of hard X-ray binary sources and their identification, on the origin of the "diffuse" galactic ridge emission, and on gamma-ray bursts.

X-ray observatories have detected an energetic outburst of radiation from the nucleus of a galaxy. This is interpreted as the disruption of a star by a very massive Black Hole located at the center of the galaxy. Such an event to occur was predicted by theory since a long time, and its proof is of large interest for different branches of astrophysics.

Progress in the kinetics of complex (dusty) plasmas is highlighted: The phase diagram of complex plasmas is presented, where the classification of different states is based on the momentum transfer rate in mutual (grain-grain) collisions. The role of the momentum transfer to the background medium (neutral gas) is analyzed, and the conditions when complex plasmas can be considered as one-phase fluids are derived. Also, the kinetics of grains with variable charges is studied, and complex plasmas are shown to be natural model systems to study non-Hamiltonian ensembles. Finally, the significance of complex plasmas for interdisciplinary studies is discussed.