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Measuring the Universe More Accurately Than Ever Before

6 March 2013. New results pin down the distance to the galaxy next door. - After nearly a decade of careful observations an international team of astronomers, among them Jesper Storm, scientist at the Leibniz-Institute for Astophysics Potsdam (AIP), has measured the distance to our neighbouring galaxy, the Large Magellanic Cloud, more accurately than ever before. This new measurement also improves our knowledge of the rate of expansion of the Universe — the Hubble Constant — and is a crucial step towards understanding the nature of the mysterious dark energy that is causing the expansion to accelerate. The team used telescopes at ESO’s La Silla Observatory in Chile as well as others around the globe. These results appear in the 7 March 2013 issue of the journal Nature.
Measuring the Universe More Accurately Than Ever Before

Stars over the La Silla Observatory, Chile. (Credit: AIP).

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).

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).


[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,

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

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.