Would it be possible to have anti-black holes, and how could we tell if we were looking at one?
Alex McDowell
London, UK
A black hole formed by the death of a star composed of antimatter would behave the same way as if its parent star had been matter. The antimatter would have as much gravity as the equivalent amount of matter. Hence, we would see no difference and it is possible that anti-black holes exist.
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Experiments at the CERN particle physics laboratory show that antimatter falls down, not up. Therefore, an antimatter black hole would still attract matter and not repel it. The anti-black hole would still get heavier with anything that falls into it, whether it be matter or antimatter.
When matter comes into contact with antimatter, the two annihilate, converting mass into energy, given by Albert Einstein’s famous equation: E = mc2. Energy, mass and information can never get out of a black hole, and so, black holes – both regular and the anti variety – get heavier by absorbing energy.
Relativity predicts white holes, but there is no experimental or observational evidence for their existence
A neutron star is formed by the death of a star that is too small to form a black hole. It could become a black hole if more matter fell onto it. However, the opposite would happen with an anti-neutron star: it would get lighter as matter fell onto it because the matter and antimatter would annihilate each other, producing energy in the form of gamma rays and pions that would be able to escape. We would then be able to detect these gamma rays.
Relativity predicts white holes, but there is no experimental or observational evidence for their existence. White holes are the opposite of black holes: they spit out matter and energy and have an event horizon through which nothing can enter. Since they are predicted to spew out matter and energy, they should be easy to detect.
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