Hi everyone,(adsbygoogle = window.adsbygoogle || []).push({});

I am a bit confused about the Penrose Process. Let's say a particle with energy E at infinity arrives in the ergoregion of a Kerr black hole and then it decays into two photons. One of them has L_1<0 and E_1<0 and hence it falls towards the singularity, while the other has L_2>0 and E_2>0. The latter photon can reach infinity (if E_2 is sufficiently high) wher an observer would detect it. By energy conservation, E_2=E-E_1 >E since E_1<0. Thus we have received a photon with an energy greater than the energy of the particle we had sent into the black hole. I mathematically understand this, but I am still puzzled. The ergosphere (the boundary of the ergoregion) is a infinite-redshift surface. Hence a photon departing from there arrives at infinity with frequency equal to zero. So, since ##E=h \nu## , I wouldn't detect anything. I can't figure out what happens to the redshift as soon as a photon comes out from INSIDE the ergoregion. Moreover, I wouldn't have more energy than the one of the particle I had sent towards the black hole. Another inconsistency is that E must be a conserved quantity (related to the Killing vector ##\partial_{t}## ), and in fact it is not if the photon is created ON the ergosphere (it would need to have E>0 to escape the black hole, but since the light is redshifted it has E=0 at infinity). Can anyone help me?

**Physics Forums - The Fusion of Science and Community**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# A Penrose Process

Tags:

Have something to add?

Draft saved
Draft deleted

Loading...

Similar Threads - Penrose Process | Date |
---|---|

A Light from the singularity of a charged black hole | Jan 21, 2017 |

A Penrose process and area theorem | Nov 9, 2016 |

Spin coefficient transformation for null rotation with $l$ fixed | Dec 30, 2015 |

Black hole, Penrose Process, SL, TL-Vector quick question | Dec 8, 2014 |

Would like to learn more about the Penrose process | Dec 6, 2009 |

**Physics Forums - The Fusion of Science and Community**