Has the merger of a neutron star and an anti-neutron star been modeled?

[Cato]

TL;DR Summary

What would happen if a neutron star and an antineutron star collided

If a neutron star and an anti neutron star collided, would they 1) completely annihilate each other, 2) form a black hole, or 3) partially annihilate each other with the remaining stars being pushed away from each other by the energy created?

 

[Drakkith]

None of those options are mutually exclusive. Often we think of annihilation as two particles interacting with each other and turning into photons (so-called 'pure energy', which is more like two particles turning into two other particles). The reality is much more complicated though, especially when you get into composite particles and high-mass particles.

Protons and neutrons (and their anti- particles) often generate a shower of pions, which themselves decay into neutrinos, photons, and muons. Beyond the possible interactions and decays of pairs or single particles, the environment in a neutron star-antineutron star annihilation would be so energetic that you'd likely generate all kinds of different particles. I'd expect a portion of the stellar material to be blasted into space along with some of this newly created matter.

So there's not really a difference between a partial and a complete annihilation, as both can leave large amounts of matter behind.

As for option 2, this can happen regardless of the annihilation process. At least some portion of the annihilation and explosion could occur inside of the event horizon formed by the merger of the two stars.

 

[Ibix]

I'd add that I don't know that I'd expect a unique answer. A direct head-on collision is likely quite a different thing from a grazing impact.

I'd also add that I doubt that anyone's modelled this because as far as I know the equations of state in the interior of neutron stars are not known with any real certainty, and they'd matter a lot here.

 

[phyzguy]

Probably nobody has spent any effort doing this because it is highly unlikely that an anti-neutron star exists in our universe.

 

[Cato]

Correct...I was thinking of "complete annihilation" as leaving behind only photons -- that was mistaken. Yes, Ibix, I could imagine a grazing impact -- at what? more than half the speed of light? -- producing something very different from a head on collision. Would be something to see. Thanks for the answers.