Black Holes and life

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Hello everyone,
im new in the forum and this is actually my first post. Im not an expert of astrophysics but for sure a very curious person that hope to can get more knowledge about astronomy and physics in the next future.

Its been kinda long time im searching an answer to some questions around black holes and ipothetical planets with life forms orbiting around them. The first doubt i had it was about how and if it was possible, so i got some info, and now i know that in theory is possible but only around rotating blackholes that we can normally find in the centre of galaxies.

If i understand it well, this kind of black holes are the one that can in theory have some planets hosting life orbiting around them because they can generate much more stable orbits than other black holes. Howhever, the ipothetical planet need to be much more lucky than only this, it should indeed be enough near to the black hole's accretion disk for get enought energy and warm, as enought distant from it for dont get sterilyzed from the ionizing emissions, and more: its orbit shouldnt enter inside the accretion disk, the ergosphere and of course shouldnt pass the event horizon.

That said, what i would like to understand is if the creatures of this planet would feel some relativistic experience being so near to the black hole. Again i went to search info about it, and what i found is that probably the planet would be already destroyed before the creatures could experience any relativistic effect (except maybe the time dilatation that anyway they wouldnt directly feel), because those effects start normally in proximity of the event horizon, so probably after the destruction of the planet due the Penrose process.

I also readed that on the two pole of a black hole, normally ergophere and event horizon are very near, so again i went to get more info about the possibility, for this planet, to have an orbit that pass from the poles (even should be a very large and "flat" one i suppose).

What i found seem suggest that the chance of such a planet are very near to be 0% (or maybe are just 0%, thats what i would like to understad here), because passing from the poles (even every very long time) would probably expose the planet to the relativistic jets that would kill everything, and even if it wouldnt happen, its orbit should be so large to dont enter the accredition disc and keep being all the time to a distance that grants warm and energy but not too much ionizing emissions (this suggest to me that the more the planet go far from the poles of the black hole, the more it should get larger its orbit).

So my question is: can theoretically be possible to have such a planet passing from the pole only during a time when there arent relativistic jets and keep being all the time enough near/far from the accretion disk and so keep life on it (in theory even till the black hole evaporete)?

Would the creatures of this planet experience any relativistic effects when the planet's orbit gets the more near possible to the pole (and so to the event horizon) for keep life surviving on it? Which one? They would see the entire universe in the sky due the gravitational lenses? They could see themself from their own back? Which other effect can theoretically happen?

Finally, passing from the pole of the black hole, is it possible to think that, once the planet is in a safe area, will be possible to see relativistic jets from the planet surface, so that they can be seen using just the eyes (and i suppose it would appear like something huge)?

Thanks to everyone that will help me to answer my doubts, im sorry if my questions can look kinda naive or even with no sense for who have a better knowledge of the topic, and also for my bad english, but as i guess you can understand, its kinda difficult to find those kind of info by myself, in internet as anywhere else.
 
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  • #2
PeterDonis
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in theory is possible but only around rotating blackholes that we can normally find in the centre of galaxies. If i understand it well, this kind of black holes are the one that can in theory have some planets hosting life orbiting around them because they can generate much more stable orbits than other black holes.

I'm not sure where you're getting this from, but it's wrong. Stable orbits around a rotating hole can be closer to the hole's horizon than stable orbits around a non-rotating hole, but this doesn't mean the former are "much more stable".

it should indeed be enough near to the black hole's accretion disk for get enought energy and warm, as enought distant from it for dont get sterilyzed from the ionizing emissions

I'm not sure where you're getting this from either. A black hole's accretion disk is expected to emit strong radiation like X rays; I'm not sure it would even be possible to find an orbit that was close enough to get significant warming from the disk without being fried by the radiation.

Can you give any specific references for where you are getting this information?

i went to search info about it, and what i found

Where?

probably the planet would be already destroyed before the creatures could experience any relativistic effect (except maybe the time dilatation that anyway they wouldnt directly feel), because those effects start normally in proximity of the event horizon, so probably after the destruction of the planet due the Penrose process

Why would the Penrose process destroy the planet?

on the two pole of a black hole, normally ergophere and event horizon are very near

Not "normally"; always. Precisely at the two poles, the boundary of the ergosphere coincides with the event horizon; as you move down from either pole towards the equator, the boundary of the ergosphere gets further above the horizon, reaching its maximum altitude above the horizon at the equator.

passing from the poles (even every very long time) would probably expose the planet to the relativistic jets

If the hole has them, then yes, they come out at the poles, so you would want to stay away from the poles.

can theoretically be possible to have such a planet passing from the pole only during a time when there arent relativistic jets

If there are jets at all, they would be expected to be there all the time.

Would the creatures of this planet experience any relativistic effects

In theory, yes. How significant they would be and how much they would affect observations would depend on how close to the hole's horizon the planet's orbit was.

They would see the entire universe in the sky due the gravitational lenses?

No. First, gravitational lensing is something an observer very far away from the hole would see. It's not something you can see in orbit around the hole. Second, the general effect of the bending of light due to the hole's gravity on observations of someone in orbit about the hole is to make the portion of the sky that is occupied by light from the rest of the universe smaller.

They could see themself from their own back?

Theoretically, in certain orbits, yes, light can circle the hole so you can see light from your own back.

Which other effect can theoretically happen?

The main other one is time dilation; the closer to the hole the orbit is, the more time dilated it is compared to distant observers. (This is the main effect portrayed in the movie Interstellar. Kip Thorne's book on the physics behind the movie might be a good source to look at.)

is it possible to think that, once the planet is in a safe area, will be possible to see relativistic jets from the planet surface, so that they can be seen using just the eyes

The jets could probably be seen with the naked eye from quite far away.
 
  • #3
DaveC426913
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No. First, gravitational lensing is something an observer very far away from the hole would see. It's not something you can see in orbit around the hole. Second, the general effect of the bending of light due to the hole's gravity on observations of someone in orbit about the hole is to make the portion of the sky that is occupied by light from the rest of the universe smaller.
Not sure I agree. Or at least, not sure I follow your logic.

An observer orbiting a BH, looking toward the BH, would be able to see what is behind the BH in a highly-distorted ring near the limb of the BH. That's essentially gravitational lensing. They may even see duplicates and even Newton's Rings.

The details of what they may see will be dependent on the mass and distance of the BH, but there's no reason gravitational lensing wouldn't be apparent.
 
  • #4
PeterDonis
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An observer orbiting a BH, looking toward the BH, would be able to see what is behind the BH in a highly-distorted ring near the limb of the BH.

In an orbit far enough away, yes. But in an orbit close enough for other relativistic effects to be significant, the area of the observer's sky occupied by the BH would be much larger, and looking in a direction that allowed them to see objects other than the BH (which would not be "toward the BH"--it would be sideways or even partly away from the BH if they were close enough) would only result in a small portion of the rest of the sky being in their field of view (and a small portion of the limb of the BH). So what they would see would be very different from what the term "gravitational lensing" is usually used to describe. The hole's gravity is still certainly bending light, but the effect is not as simple as "magnifying what's behind the hole" or "a ring near the limb of the BH".
 
  • #5
DaveC426913
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In an orbit far enough away, yes. But in an orbit close enough for other relativistic effects to be significant, the area of the observer's sky occupied by the BH would be much larger, and looking in a direction that allowed them to see objects other than the BH (which would not be "toward the BH"--it would be sideways or even partly away from the BH if they were close enough)

Yeah. The BH itself would be distorted, filling much more of the sky than expected.

What I meant by "toward the BH" is "not away from the BH". (I thought perhaps you were thinking the OP expected to see lensing when looking toward the zenith, and you were pointing that that that was wrong. Which is true.)

My blanket "The details of what they may see" alludes to the fact that things certainly would be highly distorted and highly dependent on circumstances, but not so much that lensing wouldn't be present.

...the effect is not as simple as "magnifying what's behind the hole"
Nobody said "magnifying".
Simply "would be able to see what is behind the BH [highly distorted]".
 
  • #6
PeterDonis
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What I meant by "toward the BH" is "not away from the BH".

But if you are close enough to the BH, you have to look away from the BH to see anything but a black sky (which is what the hole itself, its horizon, looks like). The closer you get to the BH, the closer to your zenith you have to look to see anything but a black sky.
 
  • #7
PeterDonis
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Nobody said "magnifying".

I understand that you didn't use that word. But that sort of effect is what the term "gravitational lensing" usually implies. Possibly the OP intended it in a broader sense, to refer to any effect due to light bending by the hole's gravity.
 
  • #8
DaveC426913
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But if you are close enough to the BH, you have to look away from the BH to see anything but a black sky (which is what the hole itself, its horizon, looks like).

If you are seeing the black of the BH, you are not looking away from it, are you? :wink:

Anyway, I think we're sympatico.

Suffice to say it's pretty tricky to describe succinctly what one might see - and notably, what happens to "direction" - near a BH.
 
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I'm not sure where you're getting this from, but it's wrong. Stable orbits around a rotating hole can be closer to the hole's horizon than stable orbits around a non-rotating hole, but this doesn't mean the former are "much more stable".



I'm not sure where you're getting this from either. A black hole's accretion disk is expected to emit strong radiation like X rays; I'm not sure it would even be possible to find an orbit that was close enough to get significant warming from the disk without being fried by the radiation.

Can you give any specific references for where you are getting this information?



Where?



Why would the Penrose process destroy the planet?



Not "normally"; always. Precisely at the two poles, the boundary of the ergosphere coincides with the event horizon; as you move down from either pole towards the equator, the boundary of the ergosphere gets further above the horizon, reaching its maximum altitude above the horizon at the equator.



If the hole has them, then yes, they come out at the poles, so you would want to stay away from the poles.



If there are jets at all, they would be expected to be there all the time.



In theory, yes. How significant they would be and how much they would affect observations would depend on how close to the hole's horizon the planet's orbit was.



No. First, gravitational lensing is something an observer very far away from the hole would see. It's not something you can see in orbit around the hole. Second, the general effect of the bending of light due to the hole's gravity on observations of someone in orbit about the hole is to make the portion of the sky that is occupied by light from the rest of the universe smaller.



Theoretically, in certain orbits, yes, light can circle the hole so you can see light from your own back.



The main other one is time dilation; the closer to the hole the orbit is, the more time dilated it is compared to distant observers. (This is the main effect portrayed in the movie Interstellar. Kip Thorne's book on the physics behind the movie might be a good source to look at.)



The jets could probably be seen with the naked eye from quite far away.
Well, about the acredition disk: i was assuming it coud be the one resource of energy and warm without a star, but if the distance cant be optimal for have a kinda warm and not sterylized planet than it simply wont work in this way and my assumption is wrong. So is it possible to have a planet orbitating around a black hole with its star also linked to the black hole? Because if im not missing something again and if i understand what you said, this could be the one chance to find a planet with life orbitating around a black hole, as the acredition disk wont work in any possible way for give the planet the right energy for life.

About the Penrose process: i readed that the matter will be devided in two parts, so i assumed a planet couldnt survive inside the ergophere because of this process, but from your words im understanding that probably im wrong again.

About the relativistic jets ok, i understand now from what you said that would be something always expected if the black hole has it, so the oribit must in any case be far from the poles if the black hole have relativistic jets.

Unluckly im searching info online, so mostly on wikipedia, i also find this (that also name the same book you named before): https://arxiv.org/pdf/1601.02897.pdf

But starting from the point that i cant understand the maths there, they are assuming anyway an universe with a background radiation...

In any case, which do you think would be a kinda realistic (and i mean even also very unlikely, but still possible) scenary of a planet hosting life around a black hole while its creatures can experiments relativistic effects (If there is at least one scenary of course)?
 
  • #10
PeterDonis
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If you are seeing the black of the BH, you are not looking away from it, are you? :wink:

If you are close enough to the BH, then yes, you will see the black of the BH even when looking in directions that are away from it. The horizon is not actually in the direction you are seeing the black of the BH in; the BH's gravity bends light so much that light that is actually coming from below you (say just outside of the limb of the BH) appears to be coming from above you.
 
  • #11
PeterDonis
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is it possible to have a planet orbitating around a black hole with its star also linked to the black hole?

Not unless both are very, very far away from the hole.

About the Penrose process: i readed that the matter will be devided in two parts, so i assumed a planet couldnt survive inside the ergophere because of this process

An object inside the ergosphere doesn't have to split into two parts. The Penrose process is a specific process that has to be designed by intelligent beings, who send objects down into the ergosphere that are designed to split into two parts, one of which comes back up with more energy than the original object went down with.

I'll take a look at the paper you referenced.
 
  • #12
DaveC426913
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The Penrose process is a specific process that has to be designed by intelligent beings, who send objects down into the ergosphere that are designed to split into two parts, one of which comes back up with more energy than the original object went down with.
Hmph. Clearly, this Penrose guy (if that's even his real name) liked 'Interstellar' so much he stole the idea and named it after himself.
 
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  • #13
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Not unless both are very, very far away from the hole.



An object inside the ergosphere doesn't have to split into two parts. The Penrose process is a specific process that has to be designed by intelligent beings, who send objects down into the ergosphere that are designed to split into two parts, one of which comes back up with more energy than the original object went down with.

I'll take a look at the paper you referenced.
This should mean that its absolutly impossible that any intelligent being can experience relativistic effects from a planet, because any orbit it will take without a star will not give the needed energy (or worst it will be too much energy) and any star with this orbitating planet should be too far from the black hole for make the creatures be affected by them.

Thanks for the explanation about the Penrose process, now its much more clear, but it mean that even a planet can theoretically survive inside the ergosphere, it anyway cant host any life form in that time if what i writed few lines above its correct.

About the papers i referenced, i think they are assuming a universe with a background radiation, which i think our universe hasnt (but at this point im not sure about it too, as i could misunderstand even it lol), so that's why i though the accretion disk was the only way to get enough radiation without a background radiation, but as it will be too much without any chance to be stable for life i must give up with no ideas about an ipothetical planet orbiting around a black hole where the creatures can experience relativistic effects, unless there is some explanation that i didnt think about or that i simply dont know its theoretically possible.
 
  • #14
DaveC426913
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This should mean that its absolutly impossible that any intelligent being can experience relativistic effects from a planet, because any orbit it will take without a star will not give the needed energy (or worst it will be too much energy) and any star with this orbitating planet should be too far from the black hole for make the creatures be affected by them.
Why not?
By what logic do you deduce that there are constraints on the supply of "needed energy"?


Also: *ahem* hypothetical
 
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Why not?
By what logic do you deduce that there are constraints on the supply of "needed energy"?


Also: *ahem* hypothetical
On the link i sended i readed this part: "Life on Earth is possible thanks to the hot Sun and the cold sky. Their temperature difference makes it possible to drive processes far from thermodynamic equilibrium by increasing the entropy elsewhere in the Universe. Absorbing photons from the Sun at ∼ 6000 K and emitting about 20 times more photons at ∼ 300 K to the cold sky makes the entropy balance sufficient to sustain complex processes in which entropy locally drops".

Assuming there is no sun/star, how this process can be done? I suppose its necessary for the life on a planet, as im sure you can give me an answer that is probably far from what i thought. :P
 
  • #16
PeterDonis
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Clearly, this Penrose guy (if that's even his real name) liked 'Interstellar' so much he stole the idea and named it after himself.

Huh? The Penrose process was clearly described by him as requiring purposeful design long before Interstellar. I have never seen anything that indicated that the Penrose process could occur naturally, since it requires a precisely controlled event to take place inside the ergosphere.

There are natural ways in which energy can be transferred from a black hole's rotation to surrounding matter (such as "superradiance"), but none of them that I'm aware of are the same as Penrose process.
 
  • #18
PeterDonis
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This should mean that its absolutly impossible that any intelligent being can experience relativistic effects from a planet, because any orbit it will take without a star will not give the needed energy

You appear to mean the needed energy for life to evolve on the planet. That may be true (though your argument is rather vague), but it's also irrelevant; observers from an advanced civilization could just fly in spaceships to the planet and land on it and experience the relativistic effects that way.

even a planet can theoretically survive inside the ergosphere, it anyway cant host any life form in that time

Quite possibly not, although our understanding of the conditions under which life in general is possible is pretty limited (since we only have one example to go on, the life on our own planet).

i think they are assuming a universe with a background radiation, which i think our universe hasnt

You have not heard of the cosmic microwave background radiation?
 
  • #19
DaveC426913
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On the link i sended i readed this part: "Life on Earth is possible thanks to the hot Sun and the cold sky. Their temperature difference makes it possible to drive processes far from thermodynamic equilibrium by increasing the entropy elsewhere in the Universe. Absorbing photons from the Sun at ∼ 6000 K and emitting about 20 times more photons at ∼ 300 K to the cold sky makes the entropy balance sufficient to sustain complex processes in which entropy locally drops".

Assuming there is no sun/star, how this process can be done? I suppose its necessary for the life on a planet, as im sure you can give me an answer that is probably far from what i thought. :P
Light/heat from the accretion disc?
Tidal forces driving geothermal processes within the planet?
A companion sun orbiting the BH?


To be clear: a stable environment for life near a black hole would be exceedingly difficult to attain and maintain - for myriad reasons - but lack of a nearby sun is not categorically one of them.
 
  • #20
PeterDonis
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Assuming there is no sun/star, how this process can be done?

There is life on Earth that does not use the entropy gradient you describe (hot Sun vs. cold sky).
 
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  • #21
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There is life on Earth that does not use the entropy gradient you describe (hot Sun vs. cold sky).

I didnt know about it, but are we talking about intelligent creatures? or micro life forms?
Light/heat from the accretion disc?
Tidal forces driving geothermal processes within the planet?
A companion sun orbiting the BH?


To be clear: a stable environment for life near a black hole would be exceedingly difficult to attain and maintain - for myriad reasons - but lack of a nearby sun is not categorically one of them.
Light/heat from the accretion disk was the first thing i though about, but you guys said me few post above that it will be kinda impossible to get enough heat and light without be grilled by radiations...im starting to be confused about it.

About tidal forces driving geothermal process within the planet i didnt think about it (and i probably couldnt think about it by myself with the knowledge i actually have), can you explain me more about it or link me something for i can try to understand it better please? The only thing i know about it is that in a huge BH like the ones in the center of the galaxies they shoud give less problems in order to dont destroy the whole planet, because their stronger effects should be felt only around the horizon.

About a companion sun orbiting the BH it was the second thing i though about, but if i understand well what you guys writed above, it should be too far from the BH for affect any creature with relativistic effects.

If you would make me an exemple of a possible evironment for life (even really unlikely, but with still very few chance to happen) near a black hole (enought near to feel relativistic effects for the creatures living on its surface) without a sun, you would make a man happy tonight.
You appear to mean the needed energy for life to evolve on the planet. That may be true (though your argument is rather vague), but it's also irrelevant; observers from an advanced civilization could just fly in spaceships to the planet and land on it and experience the relativistic effects that way.



Quite possibly not, although our understanding of the conditions under which life in general is possible is pretty limited (since we only have one example to go on, the life on our own planet).



You have not heard of the cosmic microwave background radiation?
What i mean is a planet with intelligent life forms (humanoids or anyway creatures at least able to comunicate with each other and that can possibly form a sort of society, even not an advanced society), so yea, it need the life can evolve on it.

And here we get to other doubt which leave me with no answer: as the time go slower near a BH, we can assume this society will probably be less advanced than any other society in the galaxy? If we think that in few hours on this planet can pass years for the rest of the galaxy, once on the planet will be passed some thousand year in the rest of the galaxy the time passed will be consistently much more for the creatures living enough far from the BH, this mean the creatures on a planet near a BH could evolve much slower than the rest of galaxy? What i mean is: if for the creatures near the BH the time passed its 2000 years (for exemple), during this 2000 years for the creatures sufficient far from the BH will pass maybe even 200000 years, and if this si correct near a black hole is the evolution of species theoretically slower than anywhere else? (its probably the wrong form to make this question, but i cant find a better one in english...assuming 2 societies of the same species, one near a BH, one far from it, once 2000 years pass for the society near the BH, its plausible to think that the other society far from it is much more advanced than the one in the BH proximity and that the evolution worked "faster" for them?)

I didnt know about cosmic microwave background radiation, thanks for the link, but i suppose we cant prospect an enough good environment for intelligent life on a planet around a BH counting only on that, isnt it?
 
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  • #22
PeterDonis
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are we talking about intelligent creatures?
No. Just microbes.

However, that doesn't mean intelligent creatures would not be able to develop on some other planet which only had those other entropy gradients, not the Sun/sky one. On Earth the life that uses the Sun/sky entropy gradient has filled most of the ecological niches, including the ones that favor intelligence. But on a planet where there was no Sun/sky entropy gradient, but which did have other forms of life using other entropy gradients, one of those forms of life might fill an ecological niche that favored intelligence and would therefore be under selective pressure to evolve it.

as the time go slower near a BH, we can assume this society will probably be less advanced than any other society in the galaxy?

Not necessarily. Yes, time would go slower, but we don't know how much variability there is in the time it takes for intelligent life to evolve. Again, we only have one example, our own.

i suppose we cant prospect an enough good environment for intelligent life on a planet around a BH counting only on that, isnt it?

It's hard to say. On a planet orbiting close to a BH, incoming CMB radiation would be blueshifted. (So would incoming radiation in general.) So it might end up in a part of the spectrum that was actually useful. There would also be a natural entropy gradient since outgoing radiation from the planet could just be dumped into the BH, whose effective temperature as far as the inhabitants of the planet were concerned would be even lower than the temperature of the CMB as we see it (which is the coldest part of our sky). But whether these effects would be enough to enable intelligent life to evolve is hard to tell.
 
  • #23
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No. Just microbes.

However, that doesn't mean intelligent creatures would not be able to develop on some other planet which only had those other entropy gradients, not the Sun/sky one. On Earth the life that uses the Sun/sky entropy gradient has filled most of the ecological niches, including the ones that favor intelligence. But on a planet where there was no Sun/sky entropy gradient, but which did have other forms of life using other entropy gradients, one of those forms of life might fill an ecological niche that favored intelligence and would therefore be under selective pressure to evolve it.



Not necessarily. Yes, time would go slower, but we don't know how much variability there is in the time it takes for intelligent life to evolve. Again, we only have one example, our own.



It's hard to say. On a planet orbiting close to a BH, incoming CMB radiation would be blueshifted. (So would incoming radiation in general.) So it might end up in a part of the spectrum that was actually useful. There would also be a natural entropy gradient since outgoing radiation from the planet could just be dumped into the BH, whose effective temperature as far as the inhabitants of the planet were concerned would be even lower than the temperature of the CMB as we see it (which is the coldest part of our sky). But whether these effects would be enough to enable intelligent life to evolve is hard to tell.
Ok, so theoretically is it possible to have intelligent creatures on a planet orbiting around a black hole even without sun. But so, as we cant use the accretion disk for heat and light, as we are assuming no sun, we have also to assume no light and no heat? Or the Tidal forces driving geothermal processes within the planet and/or the CMB can provide also it?

And also, if the tidal forces and/or the CMB will provide it, or if for some other reason some intelligent creature can be supposed to be present on the planet surface even without it, could be finally possible for the inhabitants of the planet try relativistic effects and keep living on the planet?

There is some possible orbit that would make the inhabitants of the planet assist to some "cosmic show" (as for the relativistic jets i mentioned before) from very "near" but still in a safe area for the life? And how it would look from a planet so near to it?

I hope im not bothering too much with many questions, thanks anyway to everyone for answer.
 
  • #24
DaveC426913
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Light/heat from the accretion disk was the first thing i though about, but you guys said me few post above that it will be kinda impossible to get enough heat and light without be grilled by radiations...im starting to be confused about it.
Yup. Very likely true.
These are not black and white options.

About tidal forces driving geothermal process within the planet i didnt think about it (and i probably couldnt think about it by myself with the knowledge i actually have), can you explain me more about it or link me something for i can try to understand it better please?
Many of Jupiter's and Saturn's moons are heated by their parent's gravity squeezing and stretching them. Have a look.

The only thing i know about it is that in a huge BH like the ones in the center of the galaxies they shoud give less problems in order to dont destroy the whole planet, because their stronger effects should be felt only around the horizon.
Yes. Larger BHs have a smaller gradient.

About a companion sun orbiting the BH it was the second thing i though about, but if i understand well what you guys writed above, it should be too far from the BH for affect any creature with relativistic effects.
You missed the point. The planet is orbiting the BH, not he star.
The BH and hte star are a binary pair. (Or perhaps the star is in orbit around the BH.)

(In Larry Niven's Integral Tees, the inhabitants live in a belt around a neutron star, which provides insufficient heat/light. But the neutron star is one of a binary pair, the second of which is a sun.)
 
  • #25
DaveC426913
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If you would make me an exemple of a possible evironment for life (even really unlikely, but with still very few chance to happen) near a black hole (enought near to feel relativistic effects for the creatures living on its surface) without a sun, you would make a man happy tonight.

Is this a story idea for a book?

This thread should be moved to the World-building forum.
 

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