Neutron stars that slow down could be eating ‘backwards’ gas

By Leah Crane

Gobbling gas from a neighbour should make neutron stars spin faster, but sometimes the exact opposite happens. Now there might be an explanation: the gas arrives “backwards”.

Neutron stars are dense, fast-spinning stellar corpses that can pull material from a smaller orbiting star, spooling it into a disc before gobbling it up. This material carries momentum, which is why the neutron star should end up spinning faster.

But when Demos Kazanas at the NASA Goddard Space Flight Center in Maryland and his colleagues looked at 18 years’ worth of X-ray observations of neutron stars in binary systems in the Small Magellanic Cloud, they found that half were slowing down.

“That’s harder to understand, because you’d think that they’d be tending to spin up if our current understanding of their evolution is correct,” says Tim Kallman, also at NASA Goddard, who wasn’t involved in the work.

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