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This answer to What defines the plane of an accretion disk around a black hole? mentions the Penrose process as a potential mechanism that could change the axis of the orbital angular momentum of an accretion disk around a black hole away from the original axis of the infaling matter's source (e.g. a companion star, a galaxy) and towards the the black hole's axis of rotation.

Here I'm just asking if the theoretical Penrose process has ever been linked to an observation, or has been used as part of a potential explanation of an observed phenomenon.

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  • $\begingroup$ We could see the orbital speed of a star around S* increasing round after round? How long should we look? $\endgroup$
    – J. Chomel
    Aug 21, 2018 at 13:29
  • $\begingroup$ @J.Chomel "Here I'm just asking if the theoretical Penrose process has ever been linked to an observation, or has been used as part of a potential explanation of an observed phenomenon." If the answer is no, then that would be the answer! $\endgroup$
    – uhoh
    Aug 21, 2018 at 14:33
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    $\begingroup$ I found Observations of the Blandford–Znajek process and the magnetohydrodynamic Penrose process in computer simulations of black hole magnetospheres which talks about the Blandford–Znajek process and of the MHD Penrose effect. Supposidely they have been both observed in computer simulations. I am not sure how the magnetohydrodynamic Penrose process and the Penrose process are related, but maybe one of you out there can explain (and move thus move towards an answer)? $\endgroup$
    – B--rian
    Mar 18, 2021 at 9:01

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A main idea for observations of astrophysical phenomena related to the (canonical) Penrose process regards the "collisional Penrose process." The canonical Penrose process involves the decay of a single particle for extracting energy from the ergosphere, but this is known to not be particularly efficient. "Collisions" of particles in the ergosphere are potentially more efficient, as "the 'collision' of multiple particles can reach arbitrarily high center-of-mass energy in the limit of extremal black hole spin." One possibility for astrophysical observations is the "potential to enhance annihilation of dark matter particles in the vicinity of a supermassive black hole."

From the discussion section of the paper by Schnittman:

Despite the wide variety of fundamental and fascinating results described in the previous sections, by most accounts the collisional Penrose process is unlikely to play a significant role in astrophysical processes. Even the highest efficiency reactions can only provide energy boosts on the order of a factor of ten or so, far below the ultrarelativistic particles seen from gamma-ray bursts or active galactic nuclei1. And in any case, even those moderately high-efficiency events require such fine tuning of initial conditions, they are probably impossible to realize in a natural setting. One potential (although admittedly speculative) exception is the annihilation of dark matter (DM) particles in the ergosphere around a Kerr black hole.... The simplest annihilation model produces two photons of equal energy and isotropic in angle in the center-of-mass frame of the reacting DM particles. These photons are then propogated to an observer at infinity, where they can be summed to produce images and spectra..... If we take the threshold center-of-mass energy to be moderate, we find that most of the annihilation photons are produced within the ergosphere region, and are thus sensitive probes of the Penrose process.

A black hole that is embedded in a uniform magnetic field can give rise to an "electromagnetic Penrose process" but it is unclear whether these effects would be observable, for example in the polarization of light as observed by the Event Horizon Telescope.

The second idea is regarding the origin of relativistic astrophysical jets, but this does not directly involve the canonical Penrose process. The currently accepted explanation for jets is the Blandford–Znajek process, although there was quite a bit of controversy surrounding it in the 1990s. The main alternatives to this process for explaining jets all have in common the so called "magnetohydrodynamical Penrose process" which is not a Penrose process per say but is instead inspired by it. From this paper:

In the original Penrose process such particles are created via close-range interaction (collisions, decay) with other particles, which gain positive energy and carry it away [see Williams (2004) for modern attempts to develop this idea in applications to astro- physical jets]. However, electrically charged particles can also be pushed on to orbits with negative energy by the Lorentz force, and this is what makes possible the so-called ‘MHD Penrose process’.

In the MHD Penrose process, the ergospheric plasma and the magnetic field play similar roles to those of the negative and positive energy particles in the canonical Penrose process. See the discussion section of this for details of why the canonical Penrose process is considered to be a special case for single particles such as photons, high frequency electromagnetic waves, and dust. The ergosphere is crucial for the Blandford–Znajek process, but it is an uncertain matter theoretically. In the future, investigations of jets may shed light on the canonical Penrose process, or other similar processes.

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The Penrose process is about extracting energy from BHs with an ergosphere. Rotating BHs have an ergosphere. Merging BHs will be rotating. In 3 cases out of 50 or more gravitational wave events at LIGO-Virgo electromagnetic waves were recorded at about the same time as the gravitational waves and from the same origin. The merger would obscure/absorb such energy in all but a narrow trajectory which may explain the low percent detection. Anyone pursuing this might consider the comparative case of spins in the same and opposing direction. I would be interested.

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  • $\begingroup$ What are the three LIGO/Virgo events with observed electromagnetic counterparts? $\endgroup$ Mar 27 at 20:07
  • $\begingroup$ No one looking at Penrose for these - GW150914 arXiv:1602.04735 - GW 170817 - S190521/GW190425. Worth keeping an eye on Wiki - List of gravitational wave observations $\endgroup$
    – Moggsy8
    Mar 29 at 4:56
  • $\begingroup$ The claimed electromagnetic counterpart of GW150914 is very uncertain. I cannot find a reference for any claimed counterpart for S190521/GW190425. Only GW170817 has an unambiguous electromagnetic counterpart..... And if no one is looking for Penrose process in these then how is this an answer to the OP's question? $\endgroup$ Mar 29 at 16:34

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