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| A schematic illustration showing how differences in the distribution of dark matter (red) alter the spin rates of modern-day spiral galaxies (left) and spiral galaxies from the early universe (right). Modern spiral galaxies tend to spin faster than their counterparts in the distant, earlier universe due to greater concentrations of dark matter near their centers. Credit: ESO/L. Calçada |
Although the invisible substance known as dark matter dominates galaxies nowadays, it was apparently only a minor ingredient of galaxies in the early universe, a new study finds.
This new finding sheds light on how galaxies and their mysterious "haloes" of dark matter have changed over time, researchers said.
Dark matter is thought to make up about 84 percent of the matter in the universe. Although dark matter is invisible, its presence can be inferred by its gravitational effects on visible matter. For instance, previous work discovered that the outer parts of galactic disks whirl faster than expected around the cores of those galaxies. These findings make sense if one assumes that "haloes" of dark matter envelop those galaxies and gravitationally pull at their outer regions. [The Search for Dark Matter in Pictures]
Now, the researchers unexpectedly find that in the early universe, dark matter played a much smaller role in galaxies than previously thought. The scientists detailed their findings in the March 16 issue of the journal Nature.
Using the European Southern Observatory's Very Large Telescope in Chile, the researchers examined six massive, star-forming galaxies from the early universe during the peak of galaxy formation 10 billion years ago. They analyzed the rotation of these galaxies to calculate how much dark matter they possessed.
Scientific American: Dark Matter Did Not Dominate Early Galaxies, Charles Q. Choi
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