News

Measuring the Universe More Accurately Than Ever Before

Kerstin Mork — 2013-03-06T23:00:00Z

Astronomers survey the scale of the Universe by first measuring the distances to close-by objects and then using them as standard candles [1] to pin down distances further and further out into the cosmos. But this chain is only as accurate as its weakest link. Up to now finding an accurate distance to the Large Magellanic Cloud (LMC), one of the nearest galaxies to the Milky Way, has proved elusive. As stars in this galaxy are used to fix the distance scale for more remote galaxies, it is crucially important.

But careful observations of a rare class of double star have now allowed a team of astronomers to deduce a much more precise value for the LMC distance: 163 000 light-years.

“I am very excited because astronomers have been trying for a hundred years to accurately measure the distance to the Large Magellanic Cloud, and it has proved to be extremely difficult,” says Wolfgang Gieren (Universidad de Concepción, Chile) and one of the leaders of the team. “Now we have solved this problem by demonstrably having a result accurate to 2%.”

The improvement in the measurement of the distance to the Large Magellanic Cloud also gives better distances for many Cepheid variable stars [2]. These bright pulsating stars are used as standard candles to measure distances out to more remote galaxies and to determine the expansion rate of the Universe — the Hubble Constant. This in turn is the basis for surveying the Universe out to the most distant galaxies that can be seen with current telescopes. So the more accurate distance to the Large Magellanic Cloud immediately reduces the inaccuracy in current measurements of cosmological distances.

"The present result reaches a new level of accuracy but we believe that the method has the potential to reach even higher (1%) accuracy. We have initiated further investigations in an attempt to reach this goal using also the AIP robotic telescope STELLA on Tenerife in Spain." points out Jesper Storm (AIP).

The astronomers worked out the distance to the Large Magellanic Cloud by observing rare close pairs of stars, known as eclipsing binaries [3]. As these stars orbit each other they pass in front of each other. When this happens, as seen from Earth, the total brightness drops, both when one star passes in front of the other and, by a different amount, when it passes behind [4].

By tracking these changes in brightness very carefully, and also measuring the stars’ orbital speeds, it is possible to work out how big the stars are, their masses and other information about their orbits. When this is combined with careful measurements of the total brightness and colours of the stars [5] remarkably accurate distances can be found.

This method has been used before, but with hot stars. However, certain assumptions have to be made in this case and such distances are not as accurate as is desirable. But now, for the first time, eight extremely rare eclipsing binaries where both stars are cooler red giant stars have been identified [6]. These stars have been studied very carefully and yield much more accurate distance values — accurate to about 2%.

Photo composition, La Silla Observatory, Chile. (Credit: AIP)

“ESO provided the perfect suite of telescopes and instruments for the observations needed for this project: HARPS for extremely accurate radial velocities of relatively faint stars, and SOFI for precise measurements of how bright the stars appeared in the infrared,” adds Grzegorz Pietrzyński (Universidad de Concepción, Chile and Warsaw University Observatory, Poland), lead author of the new paper in Nature.

(This press release was based on a release by the European Organisation for Astronomical Research in the Southern Hemisphere - ESO).

Notes

[1] Standard candles are objects of known brightness. By observing how bright such an object appears astronomers can work out the distance — more distant objects appear fainter. Examples of such standard candles are Cepheid variables [2] and Type Ia supernovae. The big difficulty is calibrating the distance scale by finding relatively close examples of such objects where the distance can be determined by other means.

[2] Cepheid variables are bright unstable stars that pulsate and vary in brightness. But there is a very clear relationship between how quickly they change and how bright they are. Cepheids that pulsate more quickly are fainter than those that pulsate more slowly. This period-luminosity relation allows them to be used as standard candles to measure the distances of nearby galaxies.

[3] This work is part of the long-term Araucaria Project to improve measurements of the distances to nearby galaxies.

[4] The exact light variations depend on the relative sizes of the stars, their temperatures and colours and the details of the orbit.

[5] The colours are measured by comparing the brightness of the stars at different near-infrared wavelengths.

[6] These stars were found by searching the 35 million LMC stars that were studied by the OGLE project.

Further information

This research was presented in a paper “An eclipsing binary distance to the Large Magellanic Cloud accurate to 2 per cent”, by G. Pietrzyński et al., to appear in the 7 March 2013 issue of the journal Nature.

Science Contat AIP: Dr Jesper Storm, +49 331 7499 394, jstorm@aip.de

Media Contact AIP: Kerstin Mork, +49 331 7499 469, 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.

Where are all the dwarfs?

Gabi Schoenherr — 2013-02-01T08:30:00Z

High-precision observations over the last two decades have indicated that our Universe consists of about 75% Dark Energy, 20% Dark Matter and 5% ordinary matter. Galaxies and matter in the universe clump in an intricate network of filaments and voids, known as the Cosmic Web. Computer experiments on massive supercomputers have shown that in such a Universe a huge number of small “dwarf” galaxies weighing just one thousandth of the Milky Way should have formed in our cosmic neighbourhood. Yet only a handful of these galaxies are observed orbiting around the Milky Way. The observed scarcity of dwarf galaxies is a major challenge to our understanding of galaxy formation.

An international team of researchers has studied this issue within the Constrained Local UniversE Simulations project (CLUES). The CLUES simulations use the observed positions and peculiar velocities of galaxies within Tens of Millions of light years of the Milky Way to accurately simulate the local environment of the Milky Way. “The main goal of this project is to simulate the evolution of the Local Group - the Andromeda and Milky Way galaxies and their low-mass neighbours - within their observed large scale environment”, said Stefan Gottlöber of the Leibniz Institute for Astrophysics Potsdam.

Analysing the CLUES simulations, the astronomers have now found that some of the far-out dwarf galaxies in the Local Group move with such high velocities with respect to the Cosmic Web that most of their gas can be stripped and effectively removed. They call this mechanism “Cosmic Web Stripping”, since it is the pancake and filamentary structure of the cosmos that is responsible for depleting the dwarfs’ gas supply.

“These dwarfs move so fast that even the weakest membranes of the Cosmic Web can rip off their gas”, explained Alejandro Benítez LLambay, PhD student at the Instituto de Astronomía Teórica y Experimental of the Universidad Nacional de Córdoba in Argentina, and first author of the publication of this study. Without a large gas reservoir out of which to form stars, these dwarf galaxies should be so small and dim that they would be hardly be visible today. The missing dwarfs may simply be too faint to see.

The study of Benítez Llambay and colleagues is published in the February issue of Astrophysical Letters.

Images / Movies

(1) www.clues-project.org/movies/cosmicwebstripping.html

(2) www.aip.de/en/news/press/cws1

(3) www.aip.de/en/news/press/cws2

Movies (1): see website for description

Image (2): Cosmic Web Stripping removes gas from a very fast dwarf galaxy crossing the local web. The image is a visualization of a CLUES simulation. The arrow symbolizes the velocity oft he dwarf, located right below (Credits: Alejandro Benítez Llambay)

Image (3): Zoom into the region where the dwarf is located (Credits: Alejandro Benítez Llambay)

Further information

Constrained Local UniversE Simulations - www.clues-project.org

Publication

Alejandro Benítez-Llambay, Julio F. Navarro, Mario G. Abadi, Stefan Gottlöber, Gustavo Yepes, Yehuda Hoffman, and Matthias Steinmetz: Dwarf galaxies and the Cosmic Web, doi:10.1088/2041-8205/763/2/L41

Scientific Contact: Dr. Stefan Gottlöber, sgottloeber@aip.de, Tel.: 0331 7499 516

Media Contact: Dr. Gabriele Schönherr, presse@aip.de, Tel.: 0331 7499383

Life possible on extrasolar moons

Kerstin Mork — 2013-01-10T08:00:00Z

The research, conducted by René Heller of Germany's Leibniz Institute for Astrophysics Potsdam and Rory Barnes of the University of Washington and the NASA Astrobiology Institute, will appear in the January issue of Astrobiology. About 850 extrasolar planets — planets outside the solar system — are known, and most of them are sterile gas giants, similar to Jupiter. Only a few have a solid surface and orbit their host stars in the habitable zone, the circumstellar belt at the right distance to potentially allow liquid surface water and a benign environment.

Heller and Barnes tackled the theoretical question whether such planets could host habitable moons. No such exomoons have yet been discovered but there's no reason to assume they don't exist.

The climatic conditions expected on extrasolar moons will likely differ from those on extrasolar planets because moons are typically tidally locked to their planet. Thus, similar to the Earth’s moon, one hemisphere permanently faces the planet. Beyond that moons have two sources of light — that from the star and the planet they orbit — and are subject to eclipses that could significantly alter their climates, reducing stellar illumination. „An observer standing on the surface of such an exomoon would experience day and night in a totally different way than we do on Earth.” explained Heller. “For instance stellar eclipses could lead to sudden total darkness at noon.”

Heller and Barnes also identified tidal heating as a criterion for exomoon habitability. This additional energy source is triggered by a moon’s distance to its host planet; the closer the moon, the stronger tidal heating. Moons that orbit their planet too closely will undergo strong tidal heating and thus a catastrophic runaway greenhouse effect that would boil away surface water and leave them forever uninhabitable.

They also devised a theoretical model to estimate the minimum distance a moon could be from its host planet and still allow habitability, which they call the "habitable edge."This concept will allow future astronomers to evaluate the habitability of extrasolar moons. "There is a habitable zone for exomoons, it's just a little different than the habitable zone for exoplanets," Barnes said.

The exquisite photometric precision of NASA’s Kepler space telescope now makes the detection of a Mars- to Earth-sized extrasolar moon possible, indeed imminent. Launched in 2009, the telescope enabled scientists to reveal thousands of new extrasolar planet candidates. Since 2012 the first dedicated “Hunt for Exomoons with Kepler” is under way.

Heller and Barnes' paper, "Exomoon Habitability Constrained by Illumination and Tidal Heating," will be published in the January issue of the journal Astrobiology.

Publication:

R. Heller, R. Barnes: Exomoon habitability constrained by illumination and tidal heating. (Preprint) In: Astrobiology, issue 01/2013.

Further Information:

The Hunt for Exomoons with Kepler (HEK) am Centre for Astrophysics der Harvard University.
Table of Exoplanets (Credits: PHL@UPR Arecibo)
Video: Visualization of the detection method used to find extrasolar moons as it is used by the HEK team at the Centre for Astrophysics at Harvard University. (Credits: Alex Parker)

Science contact: Dr René Heller, +49 331-7499-683, rheller@aip.de
Media contact: Dr Gabriele Schönherr / Kerstin Mork, +49 331-7499-469, presse@aip.de

The key areas of research at the Leibniz Institute for Astrophysics (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.

From Sunspots to Starspots

Kerstin Mork — 2012-12-06T09:00:00Z

Researchers at the Leibniz Institute for Astrophysics Potsdam (AIP) have reported the first magnetic field strength determination of a dark starspot. They have shown that starspots are indeed the locations of very strong magnetic fields, between 50-100 times stronger than the magnetic field on the rest of the surface of a star. The new tomographic iMap software, developed at the AIP, was the key to this detection. The team of researchers, led by Thorsten Carroll and Klaus G. Strassmeier, have published their results this week, as a highlight, in the Astronomy & Astrophysics journal.

By polarizing the light of stars, magnetic fields influence their radiative emission patterns. They tune the direction of oscillation in electromagnetic waves, which also changes the spectrum in a characteristic manner. The geometry of the local magnetic field on the stellar surface thus allows conclusions from its fingerprint on the spectrum in polarized light. Since starspots are very dark, and about one to two thousand degrees cooler than their surroundings, observing them is a unique challenge, requiring highly resolved spectroscopy and special analysis techniques. As Klaus G. Strassmeier says, “We receive hardly any light from the dark spots on the surface of a star. This distorts, or even suppresses, the reconstructed magnetic field distribution.“

Tomographic methods, such as the ones used in medical applications, allow for a detailed survey of the surface of a rotating star. High-quality images and spectra are obtained from the combination of many instantaneous observations. Besides the AIP, there are few institutes world-wide which have developed or made use of such tomographic methods. Additionally, the new iMap software allows for simultaneous reconstruction of temperature and magnetic field distribution along the surface of a star. This simultaneous observation of temperature and magnetic field makes magnetic fields accessible even if only very little light is available – such as in the case of observing dark starspots. These computations are very expensive. As Thorsten Carroll tells us, “In order to be able to computationally manage this complex process at all, we have trained an artificial neural network, increasing the speed of our simulations by a factor of a thousand.“

The first magnetic field in a starspot measured by astronomers was found in the solar-type star V410 Tauri, using data from the spectropolarimeter ESPaDOns at the 3.6 meter Canada-France-Hawaii Telescope on the Mauna Kea. The next targets for analysis will be more solar-type stars within the Milky Way. The detection of magnetic fields is especially relevant for stars hosting a planetary system, as the magnetic field has a significant influence on the development of such a system, and the possibility of it supporting life. Expectations are high for the next generation of spectropolarimeters, which will significantly increase the accessible sample of stars. The new spectropolarimeter PEPSI, developed at Potsdam, will gather high-quality data from the world’s largest optical telescope, the Large Binocular Telescope on 3,200 m high Mt. Graham in Arizona, from 2014 onwards.

Further information: T. A. Carroll, K. G. Strassmeier, J. B. Rice, A. Künstler: The magnetic field topology of the weak-lined T Tauri star V410 Tauri. New strategies for Zeeman-Doppler imaging. In: Astronomy & Astrophysics, 584, A95.

Science contact: Dr Thorsten A. Carroll, +49 331-7499-539, tcarroll@aip.de
Media contact: Dr. Gabriele Schönherr / Kerstin Mork, +49 331-7499-469, presse@aip.de

The key areas of research at the Leibniz Institute for Astrophysics (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.

CALIFA: The local extragalactic universe unveiled

Kerstin Mork — 2012-11-01T08:20:00Z

Together with the data release, two technical publications authored by members of the CALIFA collaboration have been made publicly available, describing the data and showing some of their scientific applications.

"I am tremendously happy to see a dream come true" says Sebastián Sánchez, Principal Investigator of CALIFA. "When we first thought of CALIFA, five years ago, the perspective of releasing such wonderful data seemed far off, yet it is happening right now! We hope and expect that the scientific community will make use of the opportunity."

Galaxies are the end products of cosmic evolution along cosmological times, and their secret history is hidden in the properties of their different components. CALIFA is an on going project running at Calar Alto Observatory, focused on characterizing the galaxies in the local universe with unprecedented detail, trying to uncover these archaeological treasures.

To this end, CALIFA uses the technique called integral field spectroscopy (IFS) to obtain data of 600 galaxies in the local universe. Traditional observational studies in extragalactic astronomy used one of two classical techniques: either imaging, which gives detailed information about the spatial extent of galaxies, or spectroscopy, which gives detailed information about many properties of galaxies, but no or very little information on the spatial distribution of them. The recent technology of IFS allows taking a multitude of simultaneous spectra at many points on each galaxy, thanks to a clever combination of fibre optics and classical techniques. CALIFA is the first IFS study to be explicitly designed as a legacy project and, upon completion, it will be the largest survey of this kind ever accomplished.

The integral field spectrograph used for the CALIFA survey at Calar Alto Observatory, PMAS (in a special configuration called PPAK) was built at AIP. It uses more than 350 optical fibres to cover a field of view of one square arcminute (equivalent to the apparent width of a 1 euro coin placed at a distance of approximately 80 metres). This way, a complete extended object, such as a galaxy, can be fully mapped in detail in just one exposure.

The delivered data allow producing maps for the different properties of galaxies, such as velocity, stellar ages or chemical composition, to mention just a few. This information will yield new insights in several key issues linked to the structure and history of galaxies in the universe. It is expected to reach results, for instance, on which processes drove galaxy evolution in time, how the chemical elements needed for life are produced inside different galaxies or at different regions inside individual galaxies, the phenomena involved in galaxy collisions. This wealth of information allows to uncover the history not only of an entire galaxy, but also of its different components.

"The amount of science we can do is simply incredible" says Jakob Walcher, from the Leibniz Institute for Astrophysics Potsdam (AIP) and Project Scientist of CALIFA. "We can study local processes that drive galaxy evolution and that happen at different places in the galaxies, such as star formation, dynamical effects etc. But we also globally characterize the properties of galaxies in the local universe in a way that was not possible before. For example we map the 2D distribution of the stellar mass and chemical elements in the galaxies. Finally, our large sample will allow us to draw comparisons between different galaxy types."

Calar Alto Observatory is jointly operated by the Max Planck Institute for Astronomy (MPIA-MPG, Heidelberg, Germany) and the Astrophysical Institute of Andalusia (IAA-CSIC, Granada, Spain). The Observatory has guaranteed 250 observing nights (distributed along three years) for the CALIFA Survey with the 3.5 m Zeiss reflector, supporting the acquisition, reduction and data storage processes. To accomplish this enormous effort the concourse of a large collaboration of astronomers is required, its composition reflecting the dual Spanish/German heritage of the Observatory. However, it also includes participants from all over the world, comprising a total of 80 people from 13 nations spread among 25 research institutes, from so far away as Australia and Canada or the USA.

AIP in particular is strongly involved in CALIFA. The instrument (PMAS) was built in Potsdam. AIP also contributed strongly to the data reduction pipeline and the project lead. Scientists at AIP will exploit the data to study the kinematics of galaxies, the abundances of the chemical elements in galaxies and the importance of AGN.

Further information:

Science contact: Dr Jakob Walcher, jwalcher@aip.de

Media contact: Kerstin Mork, +49 331-7499-469, presse@aip.de

The key areas of research at the Leibniz Institute for Astrophysics (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.