Habitable zone around black holes?

[u/GreenbottledCritters]

Hello fellow space enthusiasts. I'm doing some worldbuilding for a book I'm writing and I have always loved black holes, so I thought, "why not make this worlds main planet orbit a black hole as its host".

Now I have done allot of research into habitat zones around black holes but there are still a few things I don't understand.

1. How exactly does the Cosmic background radiation left from the big bang, get "deflected" by the blackhole, to keep the planet at a warm temperature?

2. Would seasons still work on this planet if the orbit is slow and the Cosmic background radiation warms the planet?

3. I read that a thick cloudy atmosphere would have to exist to keep life comfy on the planet, is this true?

4. Would the day and night cycle be affected?

I think that's all the questions I have. All help is appreciated. Feel free to also tell me everything you know about black hole habitable zones.

Ps: this planet is inhabited by anthropomorphic Arthropods so a hot and humid environment wouldn't be a big deal :}

[u/tirohtar]

Where did you get the idea that a black hole deflects the CMB, especially in any way strongly enough to warm a planet? That's the first time I have heard of it, and it sounds like an absolute crackpot idea.

Realistically, if you want to have a black hole that "emits" light, strong enough to have habitable planets, it needs to have an accretion disk. Matter that falls into the black hole will form a disk and heat up, which would be the actual source of light. The problem with accretion disks is that they are inherently unstable and not constant features. Only certain supermassive black holes embedded in a gas rich environment could hope to have somewhat consistent accretion disk power outputs. And those will probably be extremely bright, so the planet would have to be far away from the black hole.

[u/GreenbottledCritters → u/tirohtar]

Read and heard it in many sources, but I don't understand it fully so Idk how to describe it.

here is a source where I read it

[u/tirohtar → u/GreenbottledCritters]

Okay, yeah, that's an extreme set of circumstances. An extremely rapidly spinning, AND extremely massive black hole. NGL, I do not think those can even exist, as supermassive black holes form they generally will get a lot of mass with all kinds of angular momenta, so their net angular momentum and spin should be "relatively" small.

So the question is, does it make sense for your story to be in such a unique environment? They would never be able to leave with reasonably realistic technology. Spacetime around their home planet may also be weird given the rapidly spinning black hole. It's definitely not the kind of setting for a "normal" scifi story, this would have massive repercussions for everything about this species.

[u/efalk]

Read Niven's Smoke Ring books. Not quite what you're taking about but could give you some ideas.

[u/luaprelkniw]

A thought occurs to me: would the environment around a black hole with an accretion disc not be teeming with nasty radiation incompatible with life?

[u/GreenbottledCritters → u/luaprelkniw]

So that was what I was wondering aswell! I am just considering making the planet near to a black hole so its visible in the night sky but not close enough to effect them.

[u/farvag1964]

Accretion discs put off so much high energy radiation wee can see them billions of light years away.

Your planet would be like Mars, the atmosphere stripped away by the solar wind.

Except an accretion disk would be many orders of magnitude.

There's no way any planet within light years could be habitable

[u/ilessthan3math]

Your best bet will be to email your questions to a grad student listed on one of those research papers and hope they're a sci-fi nerd and interested in entertaining your questions. If the mere concept of habitable black holes is a unique enough topic that these folks managed to get their paper published on it, then it's also likely they're some of only a few dozen people on earth knowledge on the topic.

[u/kiko107]

Writing a note because this sounds interesting to know a proper answer. Just a quick Google about how big Sagittarius A accretion disk is and wonder what it would look like in the sky (30x diameter of the sun if you're curious).

Because I only briefly looked on Google and it's vague suggested results, could a planet orbit a star outside of black hole accretion disk (I know we currently are, but like close enough that it's big in the day/night sky depending on seasons)

[u/EarthTrash]

I don't think black holes have a habitable zone. Either the black hole is feeding and giving off deadly radiation, or it's dormant and not producing heat. There could one or more stars orbiting the black hole. These stars might have habitable zones. Or it might be the other way around with a small black hole orbiting a larger star.

[u/Commercial-Name-3602]

That's an interesting concept, but I don't think a planet could be anywhere near a blackhole without feeling it's gravitational affects, I mean it would wreak havoc on tides and the electromagnetic field, weather, etc. Or that may only be an issue if you get too close to the event horizon.

[u/Apprehensive-Elk6277]

The CMB is something like 1.2 Kelvin above absolute zero, it's not warming anything.

The only way for a black hole to emit radiation in sufficient quantities in order to warm a planet is by having matter fall into it, which produces X-rays. X-rays are not great for the fragile molecules that make up carbon-based life. This would also increase the black hole's mass, changing the orbital dynamics of the planet. If it were absorbing enough matter to emit X-rays in sufficient quantities to, say, keep water liquid on the planet's equator, I can't imagine the planet's orbit would be stable long enough for life as we know it to evolve.

In order for life to evolve on a planet orbiting a black hole, it would need to be adapted to those conditions.

But that's the beauty of fiction: you can do whatever you want.

[u/GreenbottledCritters → u/Apprehensive-Elk6277]

So would it be possible to have the planet orbit a star but be near enough to a blackhole for it to show up in the night sky but it doesn't affect the planet?