Can Hawking radiation give rise to Ultra High Energy Cosmic Rays?
July 11, 2009 by Thiago
Dyau:
The evidence so far:
- We know that Hawking radiation is emitted by all black holes. The rate at which a black hole radiates is inversely proportional to the square of its mass.
- We also know that Hawking radiation does not conserve Baryon Number. In other words, HR produces an equal number of particles and antiparticles.
- Moreover, antiparticles are routinely detected in cosmic rays of all energies. Antiprotons are one of the most precisely measured particles among the various antimatter species in cosmic rays.
Is is possible that primordial black holes in the end-stage of evaporation expire in an explosion of particles and antiparticles – which are observed here on earth as cosmic rays?
Can this mechanism explain Ultra High Energy Cosmic Rays (UHECR) – which have energies of upto 10^23 eV?
Would love to hear your thoughts!
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Daniel:
I don’t know the machanism of HR. the production of particles is continuous in energy, such as Black-Body radiation? How is the energy of the particles radiated related to the BH parameters?
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Dyau:
The rigorous theory of the HR mechanism involves quantum tunneling.
Let me explain in brief:
You must be aware of vacuum fluctuations: particle – antiparticle pairs that are constantly being created and annihilated in vacuum.
Consider a particle – antiparticle pair that is created right at the edge of a black hole’s event horizon – from the energy supplied by the black hole’s gravitational field. Usually, such a pair will annihilate almost instantaneously. However, in this case, there is a non – zero probability that one of the particles will cross the event horizon and disappear into the black hole. If this happens, the other particle/antiparticle will escape from the black hole; and the black hole will lose that much energy.
To a user at a distance, it will appear that the black hole is radiating a steady stream of particles/antiparticles; and is shrinking over time.
That, in brief, is the mechanism of Hawking Radiation.
The energy of the particles is directly proportional to the black hole’s temperature, which in turn is proportional to its surface area.
Hope this helps!
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Ragav:
Interesting idea Dyau….i have a doubt here: when the PBH ends its final stage,let’s say by explosion, then unlike the previous stage where only particles/antiparticles were radiated, now both particles and anti particles are radiated. so there is every room for them to annihilate right away and produce only photons.
so now,there is only EM radiation! if we take into consideration a single pair of particle-antiparticle, then a photon of negligible energy (but high kinetic energy due to explosion) is radiated. if we are able to calculate the energy transfer for such a process,i guess such high an energy as 10^23 ev is a little unlikely,isn’t it?!?
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Daniel:
I’ve seen that there is a strong correlation of UHECR with AGN’s (Active Galaxy Nuclei), proposed by the observatory. Also, if there were primordial BH, and if they were responsible for the Cosmic Rays, those UHECR should be isotropic in the sky. Unfortunately there are no sufficient data for that, I think.
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| Interesting idea Dyau….i have a doubt here: when the PBH ends its final stage,let’s say by explosion, then unlike the previous stage where only particles/antiparticles were radiated, now both particles and anti particles are radiated. so there is every room for them to annihilate right away and produce only photons.
so now,there is only EM radiation! if we take into consideration a single pair of particle-antiparticle, then a photon of negligible energy (but high kinetic energy due to explosion) is radiated. if we are able to calculate the energy transfer for such a process,i guess such high an energy as 10^23 ev is a little unlikely,isn’t it?!? |
Related posts:
on Mon, 13th Jul 2009 8:08 pm
You state “we know…” but a more correct statement might be “most scientists believe that Hawking radiation is probably emitted by all black holes”.
A 2004 delphi study found 10% average doubt amoung physicists polled that Hawking Radiation would actually be found to exist.
Hawking Radiation was theorized about 35 years ago but never detected and several papers refute the theory. HR may exist, it may not. It is generally accepted and expected but unknown for certain.
on Wed, 15th Jul 2009 5:21 pm
JTankers join the discussion.
on Thu, 16th Jul 2009 8:03 am
Thanks for your your suggestion, JTankers. I didn’t know 10% physicists doubted the existence of Hawking Radiation. It’s never been detected because we do not have the luxury, so far, of playing with black holes in the lab!
I am one of those who firmly believe in HR. But yes, you are right, one could use the more politically correct phrasing you have suggested.
Do join us at !