<p>A main idea for observations of astrophysical phenomena related to the (canonical) <a href="https://www.nature.com/articles/physci229177a0" rel="nofollow noreferrer">Penrose process</a> regards the &quot;<a href="https://arxiv.org/abs/1910.02800" rel="nofollow noreferrer">collisional Penrose process</a>.&quot; 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. &quot;Collisions&quot; of particles in the ergosphere are potentially more efficient, as &quot;the 'collision' of multiple particles can reach arbitrarily high center-of-mass energy in the limit of extremal black hole spin.&quot; One possibility for astrophysical observations is the &quot;potential to enhance annihilation of dark matter particles in the vicinity of a supermassive black hole.&quot;</p>
<p>From the discussion section of the paper by Schnittman:</p>
<blockquote>
<p>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.</p>
</blockquote>
<p>A black hole that is embedded in a uniform magnetic field <a href="https://arxiv.org/abs/2106.15010" rel="nofollow noreferrer">can give rise</a> to an &quot;electromagnetic Penrose process&quot; but it is unclear whether these effects would be observable, for example in the polarization of light as observed by the Event Horizon Telescope.</p>
<p>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 <a href="https://en.wikipedia.org/wiki/Blandford%E2%80%93Znajek_process" rel="nofollow noreferrer">Blandford–Znajek process</a>, although there was quite a bit of controversy surrounding it <a href="https://ui.adsabs.harvard.edu/abs/2009JKPS...54.2503K/abstract" rel="nofollow noreferrer">in the 1990s</a>. The main alternatives to this process for explaining jets all have in common the so called &quot;magnetohydrodynamical Penrose process&quot; which is not a Penrose process <em>per say</em> but is instead inspired by it. From this <a href="https://ui.adsabs.harvard.edu/abs/2005MNRAS.359..801K/abstract" rel="nofollow noreferrer">paper</a>:</p>
<blockquote>
<p>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’.</p>
</blockquote>
<p>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 <a href="https://ui.adsabs.harvard.edu/abs/2005MNRAS.359..801K/abstract" rel="nofollow noreferrer">this</a> 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 <a href="https://ui.adsabs.harvard.edu/abs/2009JKPS...54.2503K/abstract" rel="nofollow noreferrer">uncertain</a> matter theoretically. In the future, investigations of jets may shed light on the canonical Penrose process, or other similar processes.</p>

CC BY-SA 4.0
2022-03-27T20:47:51.367Z
2022-03-28T14:07:47.437Z
2022-03-28T14:07:47.437Z
Daddy Kropotkin
<p>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.</p>

CC BY-SA 4.0
2022-03-27T20:07:17.847Z
What are the three LIGO/Virgo events with observed electromagnetic counterparts?
Daddy Kropotkin
CC BY-SA 4.0
2022-03-29T04:56:02.707Z
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
Moggsy8
CC BY-SA 4.0
2022-03-29T16:34:41.407Z
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?
Daddy Kropotkin
CC BY-SA 4.0
2022-03-26T13:15:25.203Z
2022-03-26T13:15:25.203Z
Moggsy8
<p>This <a href="https://astronomy.stackexchange.com/a/26996/7982">answer to <em>What defines the plane of an accretion disk around a black hole?</em></a> mentions the <a href="https://en.wikipedia.org/wiki/Penrose_process" rel="nofollow noreferrer">Penrose process</a> 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.</p>
<p>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.</p>

CC BY-SA 4.0
2018-08-21T13:29:33.530Z
We could see the orbital speed of a star around S* increasing round after round? How long should we look?
J. Chomel
CC BY-SA 4.0
2018-08-21T14:33:30.147Z
@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!
uhoh
CC BY-SA 4.0
2021-03-18T09:01:04.807Z
I found [Observations of the Blandford–Znajek process and the magnetohydrodynamic Penrose process in computer simulations of black hole magnetospheres](https://academic.oup.com/mnras/article/359/3/801/974524) which talks about the [Blandford–Znajek process](https://en.wikipedia.org/wiki/Blandford%E2%80%93Znajek_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)?
B--rian
<black-hole><astrophysics>
Has the Penrose process ever been linked to an observed phenomenon in some way?
uhoh
# Has the Penrose process ever been linked to an observed phenomenon in some way?

(Asked by: username_0 on 2018-08-10)

This [answer to *What defines the plane of an accretion disk around a black hole?*](https://astronomy.stackexchange.com/a/26996/7982) mentions the [Penrose process](https://en.wikipedia.org/wiki/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.

**Tags:** black-hole, astrophysics
> **Comments:**
> **username_1**: We could see the orbital speed of a star around S* increasing round after round? How long should we look?  
> **username_0**: @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!  
> **username_2**: I found [Observations of the Blandford–Znajek process and the magnetohydrodynamic Penrose process in computer simulations of black hole magnetospheres](https://academic.oup.com/mnras/article/359/3/801/974524) which talks about the [Blandford–Znajek process](https://en.wikipedia.org/wiki/Blandford%E2%80%93Znajek_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)?  

---

## 2 answers

### Answer by username_3 on 2022-03-27. Score: 2

A main idea for observations of astrophysical phenomena related to the (canonical) [Penrose process](https://www.nature.com/articles/physci229177a0) regards the "[collisional Penrose process](https://arxiv.org/abs/1910.02800)." 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](https://arxiv.org/abs/2106.15010) 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](https://en.wikipedia.org/wiki/Blandford%E2%80%93Znajek_process), although there was quite a bit of controversy surrounding it [in the 1990s](https://ui.adsabs.harvard.edu/abs/2009JKPS...54.2503K/abstract). 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](https://ui.adsabs.harvard.edu/abs/2005MNRAS.359..801K/abstract):

> 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](https://ui.adsabs.harvard.edu/abs/2005MNRAS.359..801K/abstract) 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](https://ui.adsabs.harvard.edu/abs/2009JKPS...54.2503K/abstract) matter theoretically. In the future, investigations of jets may shed light on the canonical Penrose process, or other similar processes.


---

### Answer by username_4 on 2022-03-26. Score: 1

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.

> **Comments:**
> **username_3**: What are the three LIGO/Virgo events with observed electromagnetic counterparts?  
> **username_4**: 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  
> **username_3**: 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?  

---

