In Brief

3 May 2017

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

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 spin faster.

But when Demos Kazanas at the NASA Goddard Space Flight Center 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 – at the same rate as the others were accelerating.

Kazanas and his team suggest that slowdowns happen when the swallowed gas is spooling around the neutron star in the opposite direction to the star’s spin (


If backed up by further observations, the idea could drastically change our view of the way neutron stars evolve, Kazanas says.

This article appeared in print under the headline “Backspinning meal slows neutron star”