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

May 2, 2017

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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One comment on “Neutron stars that slow down could be eating ‘backwards’ gas”

  • @OP – link – The team have put forward an explanation for the slowdowns: they happen when the swallowed gas is spooling around the neutron star in the opposite direction to the star’s spin.

    It does sound plausible that stars could be spinning in the opposite direction to the direction of orbits.

    This happens with planets, and with planets and moons, so there is no reason why stars orbiting more massive stars, should not do the same.

    If formed in the gravity-field of a planet as the planet is forming, a moon will orbit the planet in the same direction as the planet is rotating and is a regular moon. If an object is formed elsewhere and later captured into orbit by a planet’s gravity, it can be captured into a retrograde or prograde orbit depending on whether it first approaches the side of the planet that is rotating towards or away from it. This is an irregular moon.

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