BY ABOUT a billion years after the big bang, our universe was reionised. Hydrogen atoms were torn apart into electrons and protons, but the perpetrator has been something of a mystery. Could dark matter be responsible?
Neutral atoms, mostly of hydrogen, formed about 380,000 years after the big bang, when the universe cooled enough for electrons and nuclei to combine. Most astronomers suspect that the hydrogen was reionised by the first generation of stars (see diagram). No telescope has ever peered far enough back in time to see the first stars form, but they are thought to have been giants, and their ferocious ultraviolet light could have done the trick.
But Dan Hooper and Alexander Belikov of Fermilab in Batavia, Illinois, think that dark matter - the unseen stuff that makes up about 85 per cent of all matter - could have reionised the universe. Dark ...
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