Reading How fast does the universe really expand? Last year a long dispute seemed settled. But now the "young savages" mess things up again. The cosmic distance ladder with which astronomers measure distances in space wobbles. Must their first "rung", the distance to our neighbor galaxy, be drastically offset? A group of young wilders are currently mixing the ideas of the old-established astronomers with new methods and results. It is astonishing that these are the circumstances in front of our cosmic front door: Our neighboring galaxy, the Large Magellanic Cloud (abbreviated to LMC, Large Magellanic Cloud) visible only from the terrestrial southern hemisphere, seems to be closer to the Milky Way for thousands of light-years than previously assumed, This borders on heresy for some researchers. After all, LMC is the first rung of a cosmic distance ladder - a series of consecutive measurement methods that astronomers use to probe to the edge of the observable universe. And not only the size of space depends on this scale, but also its rate of expansion, its age since the Big Bang, and its future.

How fast the space between galaxies and galaxy clusters expands today is described by the Hubble constant introduced by American astronomer Edwin Hubble in 1929. The figure given in kilometers per second and megaparsec (1 megaparsec = 3.26 million light-years) and fluctuated between 50 and 100 before the launch of the Space Telescope in 1990. "The consequences of the uncertainties are enormous, " says Barry Madore of the California Institute of Technology, He is a member of the key project of the Hubble Space Telescope (HST) to determine the Hubble constant. Meanwhile, the 27 astronomers of the HST key project have the Hubble constant bounded to a measurement error of ten percent (picture of the science 9/1999, "In space, there is speed 70").

The "young savages" stick to stars of the type "red lump giants" in the cosmological distance determination. They got their name because they concentrate in a narrow area ("lumps") in the so-called Hertzsprung-Russell diagram. This scheme arranges all stars on the one hand according to their spectral color or temperature, on the other hand according to their size or distance-independent luminosity. This allows the stars to be classified and, moreover, to characterize their state of development. "The brightness of red lump giants can be determined very reliably. This makes them excellent reference objects to mark out in space, "said Krzysztof Stanek of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

Stanek and others have used telescopes at the Las Campanas Observatory in Chile and the Hubble Space Telescope to precisely measure the magnitudes of several thousand Red Cluster Giants. Result: The Small and Large Magellanic Cloud revealed surprisingly low values: 182, 000 and 145, 000 light-years, respectively. In particular, the distance to the LMC causes unrest among astronomers. display

If Stanek and his colleagues are right about their data, the LMC is 10 to 15 percent closer than expected. That would increase the value of the Hubble constant by 10 to 15 percent. Such great values ​​have caused some excitement a few years ago, because it is followed by a younger age of the universe. On the other hand, the universe can not be younger than the oldest stars.

"We often hear the reaction: our measurements could not be correct because the universe would be too young, " says Stanek. "But astronomers can only determine distances as carefully as possible, and then you just have to see what results from cosmological consequences.

=== Rüdiger Vaas


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