Hot gas (shown in pink) in two merging galaxy clusters slowed down after impact, but their dark matter (blue) continued on unimpeded. Astronomers made this map of the clusters' matter distribution by studying how their mass gravitationally distorted light from background galaxies (Image: NASA/ESA/CXC/M Bradac/UCSB/S Allen/Stanford)
Dark matter seems to have separated from normal matter in a mammoth collision between two galaxy clusters.
The results bolster observations of a similar separation in the Bullet Cluster and put rough upper limits on how strongly dark matter interacts with other matter and itself. But so far they cannot rule out any of the leading dark matter candidates.
Dark matter, mysterious stuff that exerts a gravitational force on other matter, was originally proposed to explain what holds spinning galaxies, like the Milky Way, together. Observations suggest it outweighs ordinary matter by a factor of about 6 to 1.
But no one knows what it is made of, and normally dark matter and ordinary matter are too well mixed to observe the dark matter independently.
Now, isolated clouds of dark matter have been observed in a collision between two massive clusters of galaxies lying 5.7 billion light years away.
The results bolster observations of a similar separation in the Bullet Cluster and put rough upper limits on how strongly dark matter interacts with other matter and itself. But so far they cannot rule out any of the leading dark matter candidates.
Dark matter, mysterious stuff that exerts a gravitational force on other matter, was originally proposed to explain what holds spinning galaxies, like the Milky Way, together. Observations suggest it outweighs ordinary matter by a factor of about 6 to 1.
But no one knows what it is made of, and normally dark matter and ordinary matter are too well mixed to observe the dark matter independently.
Now, isolated clouds of dark matter have been observed in a collision between two massive clusters of galaxies lying 5.7 billion light years away.
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