You are here:

Astrophysics/black hole


Dear Mr. Stahl

I just wondering since i learnt about both penrose process and hawking effect. Both effects state that particle falling into Black Hole will eventually gets it negative value by "timelike and spacelike shifting" when it reached event horizon. However what about ordinary particle which enter a BH? Does it still experience a
"timelike and spacelike shifting" and gets negative value?

Thank you so much


Apart from an answer previously given, i.e.

I am not aware of any "timelike and spacelike shifting" in connection with the Hawking and Penrose processes.   For sure, it would seem that an "ordinary particle" would not remarkably affect outcomes given that particle -antiparticle pairs are being created all the time and are always being created, destroyed.

Please note also the definitional terms here: an "ordinary" particle is what you are really referring to as a "positive particle" in terms of particle-anti-particle pairs. Hence, they are already subsumed into the respective processes.

More to the point (see e.g. 'Gravitation and Inertia', p. 68), the interactions of these particles can never be observed at everyday scales of time anyway - so it's kind of like asking how many angels dance on the point of a pin.   This is why particle pairs putatively created are called "virtual pairs".

What may be getting confused here is that SOME particle orbits in the Ergosphere have a negative total potential energy, i.e. the gravitational binding energy of the orbit exceeds sums of the rest mass and the kinetic energy.  Other particle orbits will display the converse, so that the gravitational binding energy of the orbit is LESS than sums of the rest mass and the kinetic energy. These then are positive total energy orbits.

I think the key here is carefully distinguishing what is "positive" and "negative" when we look at particles in the vicinity of black holes.

If you can provide the source of where exactly you read about "timelike and spacelike shifting" in conjunction with the Penrose and Hawking processes it would also be helpful.  


All Answers

Answers by Expert:

Ask Experts


Philip A. Stahl


I specialize in stellar and solar astrophysics. Can answer questions pertaining to these areas, including: stellar structure and evolution, HR diagrams, binary systems, collapsars (black holes, neutron stars) stellar atmospheres and the spectroscopic analysis of stars as well as the magnetohydrodynamics of sunspots and solar flares. Sorry No homework problems done or research projects! I will provide hints on solutions. No nonsense questions accepted, i.e. pertaining to astrology, or 'UFOs' or overly speculative questions: 'traveling through or near black holes, worm holes, time travel etc. Absolutely NO questions based on the twaddle at this Canadian site: purporting to show a "new physics". Do not waste my time or yours by wasting bandwidith with reference to such bunkum.


Have constructed computerized stellar models; MHD research. Gave workshops in astrophysics (stellar spectroscopy, analysis) at Harry Bayley Observatory, Barbados. More than twenty years spent in solar physics research, including discovery of SID flares. Developed first ever consistent magnetic arcade model for solar flares incorporating energy dissipation and accumulation. Developed first ever loop-based solar flare model using double layers and incorporating cavity resonators. (Paper presented at Joint AGU/AAS Meeting in Baltimore, MD, May 1994)

American Astronomical Society (Solar physics and Dynamical astronomy divisions), American Geophysical Union, American Mathematical Society, Intertel.

Papers appearing in Solar Physics, Journal of the Royal Astronomical Society of Canada, Journal of the Barbados Astronomical Society, Meudon Solar Flare Proceedings (Meudon, France). Books: 'Fundamentals of Solar Physics', 'Selected Analyses in Solar Flare Plasma Dynamics', 'Physics Notes for Advanced Level', 'Astronomy & Astrophysics: Notes, Problems and Solutions', 'Modern Physics: Notes, Problems and Solutions'

B.A. degree in Astronomy; M.Phil. degree in Physics - specializing in solar physics.

Awards and Honors
Postgraduate research award- Barbados government; Studentship Award in Solar Physics - American Astronomical Society. Barbados Astronomical Society award for service (1977-91) as Journal editor.

Past/Present Clients
Caribbean Examinations Council (as advisor, examiner), Barbados Astronomical Society (as Journal Editor 1977-91), Trinidad & Tobago Astronomical Society (as consultant on courses, methods of instruction, and guest speaker).

©2017 All rights reserved.