dark matter
Nasa's Chandra & Hubble space telescopes have contributed to the best evidence for the existence of dark matter by measuring the radiation given off by two distant, colliding galaxy clusters.
Dark matter is dark because it does not absorb or emit light, by its very nature it is impossible to observe directly, only its gravitational effects can be seen and it is these effects that have just been observed.
Without any dark matter surronding the clusters, the hot gas & dust between the galaxies and the galaxies themselves would quickly fly apart. Instead of this, observations showed the hot gas & dust was slowed by a drag force which must be from dark matter. Through it's effects, astronomers worked out that the dark matter itself was not slowing down because it only interacts graviationally.
For the first time, this seems to be direct evidence for the existence of dark matter in our universe.
Will our universe turn out to be, as thought by many scientists made up mainly of dark energy & dark matter, with only around 5% being baryonic (normal) matter?
Imagine that, if all of the stars in all of the galaxies in all of the galaxy clusters in all of the super galaxy clusters in all of the universe made up on 5% of everything in the universe.
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