First stars 'may have been dark'

[Owlscrying]

The first stars to appear in the Universe may have been powered by dark matter, according to US scientists. Normal stars are powered by nuclear fusion reactions, where hydrogen atoms meld to form heavier helium.

But when the Universe was still young, there would have been abundant dark matter, made of particles called Wimps: Weakly Interacting Massive Particles.

These would have fused together and obliterated each other long before nuclear fusion had the chance to start. As a result, the first stars may have changed the course of the Universe's evolution -or at least held it up.

The leading theory is that gravity pulled balls of dark matter and hydrogen together. These 'haloes', are about a million times as massive as the Sun, and the first stars formed inside their centres.

Reactions between the Wimps, colliding and annihilating each other, would have generated enough heat to keep the protostars inflated - like hot air balloons. And as more Wimps rained down on them the heating would have kept going.

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