Studying several tens of distant galaxies, an international team of astronomers found that galaxies had the same amount of dark matter relative to stars 6 billion years ago as they have now. If confirmed, this suggests a much closer interplay between dark and normal matter than previously believed. The scientists also found that as many as 4 out of 10 galaxies are out of balance. These results shed a new light on how galaxies form and evolve since the Universe was only half its current age.
"This may imply that collisions and merging are important in the formation and evolution of galaxies", said Francois Hammer, Paris Observatory, France, and one of the leaders of the team.
The scientists were interested in finding out how galaxies that are far away - thus seen as they were when the Universe was younger - evolved into the ones nearby. In particular, they wanted to study the importance of dark matter in galaxies.
The central parts of the Milky Way, as observed in...
English: The contents of the Universe as measured ...
In mid-August 2010 ESO Photo Ambassador Yuri Belet..."Dark matter, which composes about 25% of the Universe, is a simple word to describe something we really don't understand," said Hector Flores, co-leader. "From looking at how galaxy rotates, we know that dark matter must be present, as otherwise these gigantic structures would just dissolve."
In nearby galaxies, and in our own Milky Way for that matter, astronomers have found that there exist a relation between the amount of dark matter and ordinary stars: for every kilogram of material within a star there is roughly 30 kilograms of dark matter. But does this relation between dark and ordinary matter still hold in the Universe's past?
This required measuring the velocity in different parts of distant galaxies, a rather tricky experiment: previous measurements were indeed unable to probe these galaxies in sufficient details, since they had to select a single slit,