From The Leibnitz Institute for Astrophysics[Leibniz Institut fur Astrophysik Potsdam] | AIP (DE)
5.29.24
Dr. Swetlana Hubrig
Science contact
Phone: +49 331 7499 225
shubrig@aip.de
Dr. Janine Fohlmeister
Media contact
Phone: +49 331 7499 802
presse@aip.de
Most massive star-forming region NGC346 in the Small Magellanic Cloud in the constellation Toucan in the southern starry sky located some 200 000 light years away from Earth. Credit: NASA, ESA, A. James (STScI)
For the first time, magnetic fields have been detected in three massive, hot stars in our neighboring galaxies, the Large [here] and Small Magellanic Cloud [above].
While magnetic massive stars have already been detected in our own galaxy, the discovery of magnetism in the Magellanic Clouds is especially important because these galaxies have a strong population of young massive stars. This provides a unique opportunity to study actively forming stars and the upper limit to the mass that a star can have and remain stable.
Notably, magnetism is considered to be a key component in massive star evolution, with far-reaching impact on their ultimate fate. It’s the massive stars with initially more than eight solar masses that leave behind neutron stars and black holes by the end of their evolution. Spectacular merging events of such compact remnant systems have been observed by gravitational wave observatories. Furthermore, theoretical studies propose a magnetic mechanism for the explosion of massive stars, relevant for gamma-ray bursts, x—ray flashes and supernovae. “Studies of magnetic fields in massive stars in galaxies with young stellar populations provide crucial information on the role of magnetic fields in star formation in the early Universe with star-forming gas not polluted by metals” says Dr Swetlana Hubrig, from the Leibniz Institute for Astrophysics Potsdam (AIP) and first author of the study.
Stellar magnetic fields are measured using spectropolarimetry. For this circularly polarized starlight is recorded and the smallest changes in spectral lines are investigated. However, in order to achieve the necessary accuracy of the polarization measurements, this method requires high quality data. “The method is extremely hungry for photons. This is a special challenge because even the brightest massive stars, which have more than eight solar masses, are relatively light-poor when observed in our neighbouring galaxies, the Large and the Small Magellanic Clouds,” as Dr Silva Järvinen from the AIP explains. Because of these conditions, conventional high-resolution spectropolarimeters and smaller telescopes are unsuitable for such investigations. Therefore, the low-resolution spectropolarimeter FORS2 was used, which is mounted on one of the four 8-metre telescopes of the Very Large Telescope (VLT) [below] of the European Southern Observatory (ESO).
Previous attempts to detect magnetic fields in massive stars outside our galaxy were unsuccessful. These measurements are complex and depend on several factors. The magnetic field that is measured with circular polarization is called the longitudinal magnetic field, and it corresponds exclusively to the field component that points in the direction of the observer. It is similar to the light coming from a lighthouse, which is easy to see when the beam shines towards the observer. Because the magnetic field structure in massive stars is usually characterized by a global dipole with the axis inclined to the rotation axis, the strength of the longitudinal magnetic field can be zero at rotation phases when the observer is looking directly at the magnetic equator of the rotating star. The detectability of the polarization signal also depends on the number of spectral features used to investigate the polarization. The observation of a broader spectral region with a larger number of spectral features is preferable. In addition, longer exposure times are crucial for recording polarimetric spectra with a sufficiently high signal-to-noise ratio.
Taking these important factors into account, the team carried out spectropolarimetric observations of five massive stars in the Magellanic Clouds. In two presumably single stars with spectral characteristics typical for magnetic massive stars in our own Galaxy and in one actively interacting massive binary system (Cl*NGC346 SSN7) located within the core of the most massive star-forming region NGC346 in the Small Magellanic Cloud, they succeeded to detect magnetic fields of the order of kiloGauss. On our Sun’s surface, such strong magnetic fields can only be detected in small highly magnetized regions – the sunspots. The reported magnetic field detections in the Magellanic Clouds present the first indication that massive star formation proceeds in galaxies with young stellar populations in a similar way as in our Galaxy.
See the full article here.
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The Leibnitz Institute for Astrophysics[Leibniz Institut fur Astrophysik Potsdam] | AIP (DE) is a German research institute. It is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory Potsdam (AOP) founded in 1874. The latter was the world’s first observatory to emphasize explicitly the research area of astrophysics. The AIP was founded in 1992, in a re-structuring following the German reunification.
The AIP is privately funded and member of the Leibniz Association [Leibniz-Gemeinschaft](DE). It is located in Babelsberg in the state of Brandenburg, just west of Berlin, though the Einstein Tower solar observatory [below] and the great refractor telescope on Telegrafenberg [below] in Potsdam belong to the AIP.
The key topics of the AIP are cosmic magnetic fields (magnetohydrodynamics) on various scales and extragalactic astrophysics. Astronomical and astrophysical fields studied at the AIP range from solar and stellar physics to stellar and galactic evolution to cosmology.
The institute also develops research technology in the fields of spectroscopy and robotic telescopes. It is a partner of the Large Binocular Telescope in Arizona [below], has erected robotic telescopes in Tenerife [below] and the Antarctic, develops astronomical instrumentation for large telescopes such as the VLT of the ESO [below].
Furthermore, work on several e-Science projects are carried out at the AIP.
Main research areas:
Magnetohydrodynamics (MHD): Magnetic fields and turbulence in stars, accretion disks and galaxies; computer simulations ao dynamos, magnetic instabilities and magnetic convection.
Solar physics: Observation of sunspots and of solar magnetic field with spectro-polarimetry; Helioseismology and hydrodynamic numerical models; Study of coronal plasma processes by means of radio astronomy; Operation of the Observatory for Solar Radio Astronomy (OSRA) in Tremsdorf [below], with four radio antennas in different frequency bands from 40 MHz to 800 MHz.
Stellar physics: Numerical simulations of convection in stellar atmospheres, determination of stellar surface parameters and chemical abundances, winds and dust shells of red giants; Doppler tomography of stellar surface structures, development of robotic telescopes, as well as simulation of magnetic flux tubes.
Star formation and the interstellar medium: Brown dwarfs and low-mass stars, circumstellar disks, Origin of double and multiple-star systems.
Galaxies and quasars: Mother galaxies and surroundings of quasars, development of quasars and active galactic cores, structure and the story of the origin of the Milky Way, numerical computer simulations of the origin and development of galaxies.
Cosmology: Numerical simulation of the formation of large-scale structures. Semi-analytic models of galaxy formation and evolution. Predictions for future large observational surveys.
Participation in large international research projects:
Large Binocular Telescope [above]
The Large Binocular Telescope (LBT) is on Mt. Grahams in Arizona. The LBT consists of 2 huge 8.4 m telescopes on a common mount. With their 110 square meter area, the LBT is the largest telescope in the world on a single mount, only surpassed by the combined VLTs [above] and Keck.
RAVE
The Radial Velocity Experiment measured until 2010 the radial velocities and elemental abundances of a million stars, predominantly in the southern celestial hemisphere. The 6dF multi-object spectrograph on the 1.2 m UK Schmidt telescope of the Anglo-Australian Observatory will be applied for this purpose.
Sloan Digital Sky Survey
The Sloan Digital Sky Survey (SDSS) investigates in detail a quarter of the whole sky and determine the position and absolute brightness of more than 100 million sky objects. Besides that, the distances of more than a million galaxies and quasars are estimated. With the help of this study, astronomers will be able to assess the distribution of large-scale structures in the Universe. This can provide hints about the story of the development of the Universe.
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Apache Point Observatory
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LOFAR (LOw Frequency ARray)
LOFAR is a European radio interferometer, that measures radio waves with many individual antennas in different places which it combines to a single signal. One of these international LOFAR stations has been constructed in Bornim by Potsdam and is being operated by the AIP.
Solar Orbiter
Solar Orbiter is an international mission led by the European Space Agency (ESA), with participation from NASA.
It was launched on 10 February 2020, and it will observe the Sun for at least seven years. The scientific payload consists of 10 instruments [below]: four in-situ instruments that measure the physical conditions (magnetic field, radio waves, energetic particles…) at the location of the spacecraft, and six remote sensing instruments that observe the Sun and its corona in various wavelength ranges. The AIP is involved in the operations and scientific exploitation of two instruments: the Spectrometer Telescope for Imaging X-rays (STIX), and the Energetic Particle Detector (EPD).
Technical projects:
Virtual observatory
The German Astrophysical Virtual Observatory (GAVO) is an e-Science project, that creates a virtual observation platform to support modern astrophysical research in Germany. It is the German contribution to international efforts to establish a general Virtual Observatory. GAVO enables standardized access to German and international data archives.
GREGOR
AGWs of the Large Binocular Telescope [above]
The AIP is a partner in the LBT Consortium (LBTC) and contributes financially and materially in the construction of the Large Binocular Telescope. This entails both the development and the fabrication of the optics and the mechanical and electronic components as well as the development of the software for the acquisition, guiding and wavefront sensing units (AGWs). The AGW units are essential components of the telescope and indispensable for the adaptive optics.
Multi Unit Spectroscopic Explorer (MUSE)
The Multi Unit Spectroscopic Explorer (MUSE) is an instrument of the second generation for the VLT [above] of the ESO. MUSE is optimized for the observation of normal galaxies out to very high redshift. It will furthermore deliver detailed studies of nearby normal, interacting, and starburst galaxies.
Potsdam Echelle Polarimetric & Spectroscopic Instrument (“PEPSI”)
“PEPSI” is a high-resolution spectrograph for the LBT. It will enable the simultaneous observation of circularly and linearly polarized light with high spectral and temporal resolution. The spectrograph is situated in a temperature- and pressure-stabilized room within the telescope column. The light will be conducted by fiber optics from the telescope to the spectrograph.
STELLA
STELLA Robotic Observatory on Tenerife
STELLA is a robotic observatory that consists of two 1.2 m telescopes. It is a long-term project to observe indicators of stellar activity of Sun-like stars. The operation occurs unattended — the telescopes decide the appropriate observation strategy automatically.
Observatory for Solar Radio Astronomy (“OSRA”)
“OSRA” Radio Antenna in Tremsdorf
The radio observatory “OSRA” was observing and recording radio emission from the Sun’s corona every day from 1990 until 2007. It was composed of four antennas, observing in four different frequency bands: 40–80 MHz, 100–170 MHz, 200–400 MHz and 400–800 MHz. The antennas were robotised to follow the Sun automatically. The observatory was located in Tremsdorf, near Potsdam.
4-metre Multi-Object Spectroscopic Telescope (“4MOST”)
“4MOST” is a multi-fiber, multi-spectrograph instrument that shall replace VIRCAM at the 4 m VISTA telescope and perform a 5-year survey of both galactic and extra-galactic targets.
Whereas the hardware has been designed and built by an international team of collaborators, the instrument is being assembled and tested at AIP. Contrary to most ESO projects, it shall be jointly operated by both ESO and the scientific consortium, with project management continuing to be hosted at AIP.