B So, a black hole and an antimatter star bump into each other....

[smplcrtrs]

TL;DR Summary

Black hole meets pure antimatter star, hypothetically obviously. What happens?

This is a bit hypothetical obviously as I doubt the conditions for this scenario would ever occur in the real universe.

Imagine a black hole, about 10 solar masses. It is, amazingly, sitting in an area of space that is a perfect vacuum.
Just by chance, a rogue antimatter star of exactly the mass slams into the black hole at one of its poles. There's no time for them to orbit around each other in a death waltz. Just a head-on collision.

I'm guessing the black hole is much smaller than the antimatter star, so would end up in the core very quickly. Bearing in mind there is no matter present outside the event horizon, and the star hits the black hole at one of its poles (so the ergosphere would be minimal), would the black hole be annihilated by the antimatter? If so, would the photons, neutrinos and whatever other particles are formed be able to escape the event horizon?

I was wondering whether the black hole would remain, with its mass made up entirely of the products of annihilation, sort of a photon / neutrino black hole. Or would the low mass of these particles (and the weak interaction of neutrinos) mean that the black hole would disappear in a huge nova?

I'm not a physicist, so be gentle with me. :)

 

[Ibix]

The star ends up inside the now-larger black hole. There's some messy stuff in between and some bits of the star might escape, but it's not fundamentally different from a normal matter star colliding with a black hole. The black hole is largely vacuum (in fact, entirely vacuum plus a singularity in simple models) so there's nothing to care about what's getting swallowed.

 

[smplcrtrs]

Brilliant - thank you!

 

[ergospherical]

SCNR. :)

 

[hmmm27]

Even if you assume the antimatter crosses the event horizon, bumps into some regular matter and they annihilate... doesn't matter (no pun intended) : $E=mc^2$ is an equal opportunity equation : one pound of matter plus one pound of antimatter equals two pounds of energy.

 

[Ibix]

More precisely, it would mean a lot of EM radiation with a collective mass of two pounds which still can't escape from inside the black hole. So you'd see no change externally.