News

X-ray eye in space celebrates 20 years

Six partly overlapping X-ray observations of the open star cluster NGC 2264. Credit: I. Traulsen (AIP)

X-ray eye in space celebrates 20 years

20 January 2020. At the beginning of the millennium, the European Space Agency's XMM-Newton space telescope started observing the X-ray sky. On the occasion of its 20th anniversary, scientists, in...

The XMM-Newton space telescope was successfully launched from Kourou in French Guiana on 10 December, 1999, and has been recording data since 19 January, 2000. The European consortium XMM-Newton Survey Science Centre (XMM-SSC) has now published new catalogues, prepared with state-of-the-art calibration and software, containing all X-ray detections since launch. The AIP, a founding member of the consortium, contributed software for the search of X-ray objects and was in charge of the production of one of the catalogues.

XMM-Newton has detected more than 550,000 individual celestial objects. Since some regions of the sky have been observed several times, this results in 810,795 X-ray sources in single observations. Most of the detected objects are new discoveries and often of unknown but diverse nature.

Most of these objects are supermassive black holes that are between one million and one billion times heavier than our Sun, each of which is located at the centre of its own galaxy. XMM-Newton uses its X-ray eye to detect the matter swirling around these invisible objects until it reaches the event horizon of the black hole – the point of no return, where not even light can escape the black hole's pull. Other objects in the catalogue include stars, galaxy clusters, comets and supernovae.

Axel Schwope, project manager at the AIP, explains enthusiastically: "With X-ray eyes, we can discover the part of the universe that is invisible to our eyes and dominated by extremely energetic processes and high temperatures. It is fascinating that even after 20 years in space, XMM-Newton provides first-class observational data for all possible fields of astrophysics day after day".

AIP Scientists also prepared another catalogue with information on faint sources that have been observed several times. A software developed especially for this purpose adds together overlapping observations to detect the faintest sources in the sky, increasing the number of X-ray sources discovered. These multiple observations also show how some objects change their brightness over time.

"The study of objects over a period of almost twenty years gives us a great insight into their nature. For example, changes in the brightness of X-ray light allow us to draw conclusions about the ways in which completely different objects collect matter from their surroundings. These changes can originate from stars that are torn apart in the vicinity of black holes, and some of them are not yet understood", explains Iris Traulsen, the scientist at the AIP who is responsible for the catalogue.

These catalogues enable astronomers to study high-energy objects that are often not visible to humans. The area of the sky that XMM-Newton has so far examined in great detail is about 6000 times the area of the full moon, which is still a only one fortieth of the entire sky. X-ray observations are essential to discover and understand high-energy processes in all parts of astrophysics: from the conditions around extrasolar planets to the evolution of stars, black holes and galaxies, and the study of hot gas in galaxy clusters and large structures in the universe.

 

Six partly overlapping X-ray observations of the open star cluster NGC 2264: Stars that emit light mainly at low X-ray energies appear reddish, especially hot objects at high energies appear bluish. The smaller images show, for three selected stars, the changes in brightness during a single observation (top left), the evolution of brightness over a period of thirteen years (top middle), and an X-ray spectrum showing the star's brightness at different energies ("colours") (bottom left).

Credit: I. Traulsen (AIP)

 

Catalogue website

http://xmmssc.irap.omp.eu/

IRAP press release

http://xmmssc.irap.omp.eu/4XMMprEnglish.html

Science contact AIP

Dr. Iris Traulsen, 0331 7499 286, itraulsen@aip.de

Dr. Axel Schwope, 0331 7499 232, aschwope@aip.de

Media contact AIP

Sarah Hönig, 0331 7499 803, presse@aip.de

 

The key areas of research at the Leibniz Institute for Astrophysics Potsdam (AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. The AIP has been a member of the Leibniz Association since 1992.

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Of harps, Christmas trees, a wandering star and the mysterious streams of cosmic rays

Christmas tree in the galactic centre

Of harps, Christmas trees, a wandering star and the mysterious streams of cosmic rays

19 December 2019. Researchers at the Leibniz Institute for Astrophysics in Potsdam (AIP), and the Max Planck Institute for Astrophysics in Garching (MPA), have investigated galactic radio objects t...

The inner region of our Milky Way galaxy is characterised by large amounts of warm gas, cosmic-rays and enhanced radio emission. "Astronomers have been observing planar radio-emitting magnetised structures in the galactic centre for almost twenty years. Recent observations with the MeerKAT telescope in South Africa show that these are organised into groups of almost parallel filaments, that span over a length of several light years," reports Timon Thomas from the AIP, the leading author of the study. "The filaments are seemingly sorted by their length, so that they look like the strings of a harp." Hence, researchers from Potsdam and Garching called these objects radio synchrotron harps. Synchrotron is the name of the mechanism that generates the radio emission. It arises when charged particles like electrons are accelerated in magnetic fields.

"The observed structures are created when massive stars or pulsars fly through an ordered magnetic field and discharge cosmic ray particles along their path into these magnetic fields," explains co-author Christoph Pfrommer from AIP. "The particles propagate along the magnetic field lines, usually transverse to the stellar orbit, causing the magnetic fields in the radio regime to light up and appear like the strings of a harp."

So far, the exact transport process of the particles along these strings has been a mystery. The researchers now assume that the individual strings show a chronological sequence in which the particles have spread along the magnetic field lines from their point of release. If this propagation was a diffusion process, the structures seen in the radio observations should have rounded bell shapes, but they do not. By measuring one of the harps and performing detailed model calculations, the astrophysicists were able to show that streaming must be the most important transport process of cosmic rays. "The particles 'pluck' the strings and stimulate the magnetic fields to oscillate, which in turn hold the particles together to form a streaming fluid," explains Torsten Enßlin from the MPA, the initiator of the study.

With this illuminating Advent insight, the decades-old mystery of the transport of cosmic ray particles has been solved. Contrary to the previous assumption of diffusing particles, it turns out that they mainly stream.

 

Radio synchrotron harp and Christmas tree in the galactic centre.
Left: The synchrotron radiation of the particles traces the magnetic field lines, making them visible in the form of harp strings.
Right: The star which emitted the particles moved through the centre of this structure, from bottom to top, and is now at its tip. The particles flow left and right along the horizontal magnetic field lines.

Credit: T. Thomas (AIP) / MeerKat


The observed brightness profiles of the radio emission along the investigated harp strings are compared to model calculations (orange) with streaming (left) and with diffusion (right). In the lower two profiles, where the particles had more time to spread, the models show clear differences. The one with streaming can explain the observed profiles well while the one with diffusion only shows clear deviations. The importance of streaming thus visibly increases with time and should thus be the more important contribution to the transport of cosmic rays over even greater distances in our Galaxy.
Credit: Thomas, Pfrommer, & Enßlin (2019)

 

Publications

Timon Thomas, Christoph Pfrommer, and Torsten Enßlin: Probing Cosmic Ray Transport with Radio Synchrotron Harps in the Galactic Center.  preprint:  https://arxiv.org/abs/1912.08491

Heywood, I., Camilo, F., Cotton, W. D., et al. (2019): Inflation of 430-parsec bipolar radio bubbles in the Galactic Centre by an energetic event. Nature, 573, 235

 

MPA press release

https://www.mpa-garching.mpg.de/786348/news20191219

 

Science contact AIP

Timon Thomas, 0331 7499 513, tthomas@aip.de
Prof. Dr. Christoph Pfrommer, 0331 7499 531, cpfrommer@aip.de

 

Media contact AIP

Dr. Janine Fohlmeister, 0331 7499 802, presse@aip.de

 

The key areas of research at the Leibniz Institute for Astrophysics Potsdam (AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. The AIP has been a member of the Leibniz Association since 1992.

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Three supermassive black holes discovered at the core of one galaxy

The irregular galaxy NGC 6240 with three black holes. Credit: P. Weilbacher (AIP), NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)

Three supermassive black holes discovered at the core of one galaxy

21 November 2019. An international research team led by scientists from Göttingen and Potsdam have for the first time shown that the galaxy NGC 6240 contains three supermassive black holes. The un...

Massive galaxies like the Milky Way typically consist of hundreds of billions of stars and host a black hole with a mass of several million up to several 100 million solar masses at their centres. The galaxy known as NGC 6240 is classified as an irregular galaxy due to its particular shape. Until now, astronomers have assumed that it was formed by the collision of two smaller galaxies and therefore contains two black holes in its core. These galactic ancestors moved towards each other at velocities of several 100 km/s and are still in the process of merging. The galaxy system is around 300 million light years away from us – close by cosmic standards –, has been studied in detail at all wavelengths, and has so far been regarded as a prototype for the interaction of galaxies.

“Through our observations with extremely high spatial resolution we were able to show that the interacting galaxy system NGC 6240 hosts not two – as previously assumed – but three supermassive black holes in its centre,” reports Professor Wolfram Kollatschny from the University of Göttingen, the leading author of the study. Each of the three heavyweights has a mass of more than 90 million Suns. They are located in a volume of space of less than 3000 light-years across, i.e. in less than one hundredth of the total size of the galaxy. “Such a concentration of three supermassive black holes has so far never been discovered in the universe,” adds Dr. Peter Weilbacher of the Leibniz Institute for Astrophysics Potsdam (AIP). “The present case provides evidence of a simultaneous merging process of three galaxies along with their central black holes.”

The discovery of this triple system is of fundamental importance for understanding the evolution of galaxies over time. So far it has not been possible to explain how the largest and most massive galaxies, which we know from our cosmic environment in the “present time”, were formed merely through normal galaxy interaction and merging processes over the course of the last 14 billion years, i.e. the approximate age of our universe. “If, however, simultaneous merging processes of several galaxies took place, then the largest galaxies with their central supermassive black holes were able to evolve much faster,” Peter Weilbacher summarizes. “Our observations provide the first indication of this scenario.”

The unique high-precision observations of galaxy NGC 6240 were obtained using the 3D MUSE spectrograph mounted on the 8m VLT telescope in Chile, a telescope operated by the European Southern Observatory (ESO). The spectrograph was used in spatial high-resolution mode together with four artificially generated laser stars and an adaptive optics system. Thanks to this sophisticated technology, images could be obtained with a sharpness similar to that of the Hubble Space Telescope, but with the added benefit of having a spectrum for each image pixel. These spectra were essential in determining the motion and masses of the supermassive black holes in NGC 6240.

The scientists predict that the imminent merging of the supermassive black holes in a few million years will also generate very strong gravitational waves. In the foreseeable future, signals of similar objects can be measured with the planned satellite-based gravitational wave detector LISA, and further merging systems can be discovered.

 

The irregular galaxy NGC 6240. New observations show that it harbours not two but three supermassive black holes at its core. The northern black hole (N) is active and was previously known. The zoomed-in new high-spatial resolution image shows that the southern component consists of two supermassive black holes (S1 and S2). The green colour indicates the distribution of gas surrounding the black holes that is ionized by radiation. The red lines show the contours of the star light from the galaxy and the length of the white bar corresponds to 1000 light years.

Credit: P. Weilbacher (AIP), NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)

 

Original Publication

W. Kollatschny, P. M. Weilbacher, M. W. Ochmann, D. Chelouche, A. Monreal-Ibero; R. Bacon, T. Contini: NGC6240: A triple nucleus system in the advanced or final state of merging, Astronomy & Astrophysics, 2019

DOI:  https://doi.org/10.1051/0004-6361/201936540

University of Göttingen press release

http://www.uni-goettingen.de/en/3240.html?id=5719

Science contact AIP

Dr. Peter Weilbacher, 0331 7499 667, pweilbacher@aip.de

Media contact AIP

Dr. Janine Fohlmeister, 0331 7499 802, presse@aip.de

 

The key areas of research at the Leibniz Institute for Astrophysics Potsdam (AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. The AIP has been a member of the Leibniz Association since 1992.

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An overlooked piece of the solar dynamo puzzle

The most sunspots and, thus, the greatest magnetic activity are located close to the solar equator. Scientist have now demonstrated for this region a specific magnetic instability, that was considered impossible so far. Credit: NASA/SDO

An overlooked piece of the solar dynamo puzzle

28 October 2019. A previously unobserved mechanism is at work in the Sun’s rotating plasma: a magnetic instability, which scientists had thought was physically impossible under these conditions. ...

Just like an enormous dynamo, the Sun’s magnetic field is generated by electric currents. In order to better understand this self-reinforcing mechanism, researchers must elucidate the processes and flows in the solar plasma. Differing rotation speeds in different regions and complex flows in the Sun’s interior combine to generate the magnetic field. In the process, unusual magnetic effects can occur – like this newly discovered magnetic instability.

Researchers have coined the term “Super HMRI” for this recently observed special case of helical magnetorotational instability (HMRI). It is a magnetic mechanism that causes the rotating, electroconductive fluids and gases in a magnetic field to become unstable. What is special about this case is that the Super HMRI requires exactly the same conditions that prevail in the plasma close to the solar equator – the place where astrophysicists observe the most sunspots and, thus, the Sun’s greatest magnetic activity. So far, however, this instability in the Sun had gone unnoticed and is not yet integrated in models of the solar dynamo.

Nonetheless, it is known that magnetic instabilities are crucially involved in many processes in the universe. Stars and planets, for example, are generated by large rotating disks of dust and gas. In the absence of a magnetic field, this process would be inexplicable. Magnetic instabilities cause turbulence in the flows within the disks and thus enable the mass to agglomerate into a central object. Like a rubber band, the magnetic field connects neighboring layers that rotate at different speeds. It accelerates the slow particles of matter at the edges and slows down the fast ones on the inside. There the centrifugal force is not strong enough and the matter collapses into the center. Near the solar equator it behaves precisely the other way around. The inner layers move more slowly than the outer ones. Up to now, experts had considered this kind of flow profile to be physically extremely stable.

The researchers at HZDR, the University of Leeds and AIP decided to investigate it more thoroughly. In the case of a circular magnetic field, they had already calculated that even when fluids and gases were rotating faster on the outside, magnetic instability could occur. However, only under unrealistic conditions: the rotational speed would have to increase too strongly towards the outer edge. Trying another approach, they now based their investigations on a helical magnetic field. “We didn’t have any great expectations, but then we were in for a genuine surprise,” HZDR’s Dr. Frank Stefani remembers – because the magnetic instability can already occur when the speed between the rotating layers of plasma only increases slightly – which happens in the region of the Sun closest to the equator.

“This new instability could play an important role in generating the Sun’s magnetic field,” Stefani estimates. “But in order to confirm it we first need to do further numerically complicated calculations.” Prof. Günther Rüdiger of AIP adds, “Astrophysicists and climate researchers still hope to better understand the cycle of sunspots. Perhaps the ‘Super HMRI’ we have now found will take us a decisive step forward.”

With its various specialisms in magnetohydrodynamics and astrophysics, the interdisciplinary research team has been investigating magnetic instabilities – in the lab, on paper and with the aid of sophisticated simulations – for more than 15 years. The scientists want to improve physical models, understand cosmic magnetic fields and develop innovative liquid metal batteries. Thanks to close cooperation, in 2006, they managed to experimentally prove the theory of magnetorotational instability for the first time. They are now planning the test for the special form they have predicted in theory: In a large-scale experiment that is currently being set up in the DRESDYN project at HZDR, they want to study this magnetic instability in the lab.

 

Original Publication

G. Mamatsashvili, F. Stefani, R. Hollerbach, G. Rüdiger: Two types of axisymmetric helical magnetorotational instability in rotating flows with positive shear, in Physical Review Fluids, 2019

DOI: https://doi.org/10.1103/PhysRevFluids.4.103905

HZDR press release

https://www.hzdr.de/db/Cms?pOid=59692&pNid=0

Science contact

Dr. Günther Rüdiger, gruediger@aip.de

Media contact AIP

Sarah Hönig, 0331 7499 803, presse@aip.de

 

The key areas of research at the Leibniz Institute for Astrophysics Potsdam (AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. The AIP has been a member of the Leibniz Association since 1992.

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eROSITA – first glimpse into the hot universe

eROSITA first light: The Large Magellanic Cloud as seen with the seven "X-ray eyes" of eROSITA. Credit: F. Haberl, M. Freyberg, C. Maitra, MPE/IKI

eROSITA – first glimpse into the hot universe

22 October 2019. The German space telescope eROSITA has now published the first astounding images of the hot universe. With all seven “X-ray eyes” it targeted a rare neutron star, the Large Mag...

The X-ray telescope eROSITA (extended ROentgen Survey with an Imaging Telescope Array), the main instrument of the Russian-German Spectrum-X-Gamma (SRG) mission, which was successfully launched in July, has now reached its orbit around Lagrange Point 2, 1.5 million kilometers behind Earth when viewed from the Sun, after a flight time of more than three months. From here, eROSITA will begin a survey of the entire sky to produce a map of the hot structures in the universe that emit X-rays due to their high temperature.

eROSITA consists of seven individual telescope modules that collect the incident X-ray light from the hot sources of the universe. Initially, only individual components were switched on and their functionality was carefully checked step by step. At first, individual telescope modules showed anomalies. Cosmic radiation is suspected of being the “culprit”, which could have triggered small changes in some components. By now, eROSITA has gone into operation after a short delay and tests.

In its full configuration, i.e. operated with all seven cameras, eROSITA was first aligned toward an object proposed by AIP (Figure 1). Project manager Axel Schwope explains why exactly this object was selected: “It is a very exotic object, Pulsar PSR B0656+14, a rapidly rotating isolated neutron star, which is best visible in X-ray light due to its small size and its enormously high temperature of more than one million degrees.” Such objects are extremely rare, about 30 are known, but they allow fundamental physical insights into cosmic laboratories. Neutron stars like PSR B0656+14, which only needs one third of a second for a full rotation, has a diameter of only about 30 km and a mass of about one and a half solar masses, may also be described as macroscopic atomic nuclei. In total, eROSITA observed the pulsar for 28 hours. At the same time, the European X-ray satellite XMM-Newton also targeted the object. The combined observation allows new, unique insights into the magnetic field and the temperature distribution of the neutron star. “Both instruments cooperate wonderfully. Thanks to the high spectral and temporal resolution now available, we can obtain a spectrum at each moment of rotation that provides information about the extreme physics of a neutron star,” explains Schwope.

 

Figure 1: Pulsar PSR B0656+14, an isolated and rapidly rotating neutron star about 900 light years from Earth. The observation nicely illustrates the survey power of eROSITA through its large field of view, about twice as large as that of XMM-Newton, which thus uncovers many previously unidentified X-ray sources surrounding the pulsar: hot stars in the Milky Way (mostly greenish sources) and distant active galactic nuclei (mostly bluish sources).

Credit: A. Schwope, G. Lamer, I. Traulsen (AIP), C. Maitra, M. Ramos-Ceja (MPE), MPE/IKI

In our neighboring galaxy, the Large Magellanic Cloud, eROSITA not only shows the distribution of diffuse hot gas, but also some remarkable details, such as supernova remnants like SN1987A (Figure 2). The eROSITA observations now confirm that this source is becoming fainter, as the shock wave produced by the stellar explosion observed in 1987 expands through the interstellar medium. In addition to a host of other hot objects in the Large Magellanic Cloud itself, eROSITA also reveals a number of foreground stars from our own Milky Way galaxy as well as distant active galactic nuclei, whose radiation pierces the diffuse emission of the hot gas in our neighboring galaxy.

 

Figure 2: Our neighboring galaxy, the Large Magellanic Cloud, observed in a series of exposures with all seven eROSITA telescope modules taken from 18 to 19 October 2019. The diffuse emission originates from the hot gas between the stars with temperatures of typically a few million degrees. The more compact nebulous structures in the image are mainly supernova remnants. The most prominent one, SN1987A, is seen close to the center as a bright source which appears punctate due to the great distance.

Credit: F. Haberl, M. Freyberg, C. Maitra, MPE/IKI

A particular focus of eROSITA is the discovery and mapping of galaxy clusters. These clusters bind the extremely diluted gas from their surroundings, which is invisible to our eyes, by gravity. Through compression and turbulence, the gas heats up and radiates intensively in the X-ray range. Among eROSITA’s first images are the interacting galaxy clusters A3391 and A3395 (Figure 3). The two clusters, which appear in the images as large elliptical nebulae, extend over millions of light years and contain thousands of galaxies each. During its 4-year X-ray survey, eROSITA will discover and map about 100,000 galaxy clusters and several million active black holes in the centers of galaxies.

 

Figure 3: The two interacting galaxy clusters A3391, above, and A3395, below, observed in a series of exposures with all seven eROSITA telescope modules taken from 17 to 18 October 2019. The individual images were subjected to different analysis techniques, and then colored in different schemes to highlight the different structures. In the left-hand image, the red, green and blue colours refer to the three different energy bands of eROSITA. One clearly sees the two clusters as nebulous structures, which shine brightly in X-rays due to the presence of extremely hot gas (tens of millions of degrees) in the space between galaxies. The image on the right highlights the “bridge” or “filament” between the two clusters, confirming the suspicion that these two huge structures actually do interact dynamically. The eROSITA observations also show hundreds of point-like sources, signposting either distant supermassive black holes or hot stars in the Milky Way.

Credit: T. Reiprich (Univ. Bonn), M. Ramos-Ceja (MPE), F. Pacaud (Univ. Bonn), D. Eckert (Univ. Geneva), J. Sanders (MPE), N. Ota (Univ. Bonn), E. Bulbul (MPE), V. Ghirardini (MPE), MPE/IKI

The German X-ray telescope eROSITA was developed and built with the support of DLR Space Management by the Max Planck Institute for Extraterrestrial Physics in Garching together with the Leibniz Institute for Astrophysics Potsdam (AIP) and the universities of Erlangen-Nuremberg, Hamburg and Tübingen. The universities of Munich and Bonn also participated in the science preparation for eROSITA. The partner institutes have developed software for data analysis, mission planning and simulations and provided parts of the hardware. The Russian partner Institute is the Space Research Institute IKI in Moskow; NPOL, Lavochkin Association, in Khimky near Moskow, is responsible for the technical implementation of the whole SRG mission, which is a joint project of the Russian and German space agencies, Roscosmos and DLR.

 

MPE press release

http://www.mpe.mpg.de/7362095/news20191022

DLR press release

https://www.dlr.de/EN

Science contact

Dr. Axel Schwope, 0331 7499 232, aschwope@aip.de

Media contact

Sarah Hönig, 0331 7499 803, presse@aip.de

 

The key areas of research at the Leibniz Institute for Astrophysics Potsdam (AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. The AIP has been a member of the Leibniz Association since 1992.

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