News

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.

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.

The 2019/2020 Starry Nights season will start with a guest lecture on Alexander von Humboldt's Cosmos Lectures on the occasion of the Humboldt Year. Afterwards, scientists from AIP will continue the popular public lecture series. The topics reflect the diversity of the institute's research: from exoplanets and Sun-like stars to dark matter, special galaxies and space missions, the comprehensible lectures offer anyone interested an insight into current topics in astrophysics. All lectures are in German language. After the talks, we offer a tour over the AIP campus and – if possible – an observation with one of our historical reflecting telescopes.

Please check the German site for a short description of this week's topic.

We look forward to your visit! Admission is free, no previous registration is necessary.

Venue: AIP, An der Sternwarte 16, 14482 Potsdam

Further dates: Starry Night in Babelsberg

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.

Prof. Newton's research deals with the physics of stars and their planets, in particular with long-lived low-mass M-class dwarf stars, their rotation and magnetism, and the formation of exoplanets.

Prof. Newton received her doctorate from Harvard University with a thesis on M dwarf stars and subsequently researched M dwarf stars as host stars of planets as a Postdoctoral National Science Foundation Fellow at Massachusetts Institute of Technology. Since the beginning of the year she has been Assistant Professor of Physics and Astronomy at Dartmouth College in New Hampshire, USA.

Her work on the rotation of very low-mass M dwarf stars has attracted much attention and offers direct links to AIP research on stellar activity and exoplanets. M dwarf stars have such low luminosity that not one is visible from Earth with the naked eye, even though they make up a large percentage of all stars.

Artist’s impression of an M dwarf star with planets. Credit: NASA/JPL-Caltech

Schedule of the award ceremony

From 3:00 pm

• Opening by Prof. Dr. Matthias Steinmetz, Scientific Chairman at AIP
• Welcome by Dr. Jürgen Kroseberg, Federal Ministry of Education and Rsearch
• Laudation by Prof. Dr. Katja Poppenhäger, section head of Stellar physics and exoplanets at AIP
• Award ceremony
• Ceremonial lecture by Prof. Dr. Elisabeth Newton “Spin and magnetism in M dwarf stars”
• Reception

About the Wempe Award

In honor of Prof. Dr. Johann Wempe (1906 - 1980), the last director of the former Astrophysical Observatory of Potsdam, the Johann Wempe Award, first awarded in 2000, is granted to an outstanding scientist. The award is financed from funds left in the will of Johann Wempe.

Former recipients are Alice Quillen, Oliver Gressel, Brent Tully, Thomas R. Ayres, Yehuda Hoffman, Matthias Rempel, Kenneth C. Freeman, Ignasi Ribas, Eva Grebel, Alexander Kosovichev, Isabelle Baraffe und Gilles Chabrier, Russell Cannon and Tom Abel.

Science contact

Prof. Dr. Katja Poppenhäger, 0331 7499 521, kpoppenhaeger@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.

Sydney Barnes, leader of the stellar activity group at AIP and organizer of the conference, states: “This rotation seems to be the fundamental variable underlying many dynamical behaviors of stars such as the magnetic activity manifested in stellar dynamos, starspots, and solar or stellar flares. One application of measured stellar rotation rates is to derive the ages of stars, otherwise difficult to obtain.” These ages are helping to construct astronomical chronologies, that is, the dating of astronomical phenomena. Silva Järvinen, AIP-scientist in the stellar physics and exoplanets section, adds: “The AIP has played a leading role over the past decades in efforts to understand these magnetic phenomena for a large variety of stars, and also to measure related manifestations such as starspots, stellar magnetic fields, and rotation itself.” The rotation rates of increasingly large numbers of stars can now be measured precisely using telescopes on earth and also in space.

This conference will bring together an international cross-section of major contributors to the field to discuss the latest findings, and to put them in perspective. More information on this event is available at the conference website: https://thinkshop.aip.de/16.

Scientific contacts

Dr. Sydney Barnes, 0331-7499-379, sbarnes@aip.de

Dr. Silva Järvinen, 0331-7499-448, sjarvinen@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.