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Posted by ajsh/">ajsh on October 16, 1999 14:31:11 UTC

> A problem with Hawking Radiation?? > >: This states where a particle/antiparticle pair are formed one can fall into a blackhole and the other is "emitted". > >: Okay so what stops this particle that has escaped just >: cancelling out with another "emitted" -antiparticle which has also just escaped?? > >: For this reason surely this theory is not correct!!

Both particle and anti-particle emerge with positive mass-energy. If they annihilate with each other, they will still produce photons which can be seen. As a practical matter, the Hawking radiation from astronomical sized black holes is almost entirely photons (photons are their own anti-particle).

> Anti-matter blackhole?? > >: Would this be any different to a blackhole made of collapsed matter? > >: How would two black hole's -one of collapsed matter/the other of collapsed anti-matter interact??

No difference. All the information about the nature of the mass is lost into the singlarity, except for the information about globally conserved quantities, the mass, charge and angular momentum.

> Re: Can two Black hole's exist side by side??


>: Just far enough away so that they don't collapse into each other?? > >: What would occur at the point where the forces's of each where in exact balance??

They orbit each other. Not much different from the Earth orbiting the Sun, except that the black holes will emit much more powerful gravitational radiation. The gravitational radiation causes the BHs to spiral in, initially slowly. Eventually the BHs merge in a spectacular burst of gravitational radiation, which it is hoped that future gravitational wave telescopes like LIGO may see.

>Re: Is what we see in the Quantum world the result of Blackhole's??

There may be a connection. It is likely that an ultimate theory of particles (e.g. superstrings) involves gravity in a fundamental way.

>: As we know particle /antiparticle pairs appear then disappear..

No. Annihilating particle/antiparticle pairs produce energy, photons.

>: Is this the energy/mass that collapse's into a blackhole just appearing somewhere else in space & time??

In the standard theory, no. But since there is no definitive theory of what happens at the singularities of black holes, one cannot be sure.

>: Does gravity affect the frequency at which these particles appear??

There is something called the gravitational redshift. Is that what you are talking about?

> Re: Man made black hole?? > >: What would you need to do to create one??

A lot of mass in a tiny space. E.g. take the whole earth and compress it down to a cubic centimetre. Or take a mountain and compress it to the size of a proton.

Nature manages to create black holes in two ways: 1. the core collapse of a very massive star that goes supernova; 2. the collapse of the central core of a galaxy.

> Re: Could you live near a blackhole?? > >: Theory suggests that bigger the black hole -the further out the event horizon will be.


>: Would it be possible to have an event horizon where the forces are similar to earth's gravity??ie not deadly.

Yes. You have to go to supermassive black holes to prevent things getting ripped apart. The tidal force between your feet and toes is 1 g at the horizon of a 30,000 solar mass black hole. But you can survive if you keep away from it. E.g. if the Sun were a black hole, and the Earth were orbiting it, the gravitational forces would be the same as they are.

>: If so it would be great for waste disposal!!

The Sun's not a bad incinerator either.

Cheers, Andrew Hamilton

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