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The Rygyphae are a species that lives in the geothermal pockets, areas heated by volcanic activity. The rest of the planet is nothing but frozen ice and rock, but these pockets are lush jungles full of thriving life.

Is this feasible? Do these geothermal pockets have everything they need for ecosystems like this to form in them?

It is my understanding that a planet orbiting a black hole receives only light, and no heat, so therefore if the heat is supplied by volcanic activity, then jungles should be able to grow, right?

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    $\begingroup$ I'm not convinced your premise of 'light, not heat' is correct regarding black holes. If anything, it would be the exact opposite as a result of Hawking Radiation. Also, some black holes appear to emit plasma plumes, which would be amazingly hot. Do you have a reference link for this statement? As for ecosystems that survive on geothermal heat, look at black smokers in the deep ocean. $\endgroup$ – Tim B II May 11 '18 at 5:24
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    $\begingroup$ @Vincent What's the cause of this planet being likely to have no atmosphere? Is it related to the black hole? These Pockets are on the surface, although I may have to change that if it's unlikely to have an atmosphere. $\endgroup$ – Sydney Sleeper May 11 '18 at 5:37
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    $\begingroup$ Got it. So, Hawking Radiation too low for meaningful heat, and the light being the result of inbound super heated gasses, not the black hole itself. I'll do some more research on smoker ecosystems and post an answer when I get the chance... $\endgroup$ – Tim B II May 11 '18 at 5:41
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    $\begingroup$ thriving life Define that. Are we talking about single celled organisms or walking talking beings or something in between. I'd have said single but complex lifeforms like mammals sounds really, really unlikely. Jungles would be a real stretch. $\endgroup$ – StephenG May 11 '18 at 5:54
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    $\begingroup$ Lush jungles = just like they developed on earth only about 200 million years ago (sorry if I'm off by a couple of years) after billions of years of other life given a completely different scenario? Now that doesnt make sense in any sense no matter what. Either don't question it and just go with it or think for a minute: alien life could be anything. I had a discussion with a physics professor once who was sure it exists inside stars. Ask yourself what you really mean by jungle. $\endgroup$ – Raditz_35 May 11 '18 at 8:38
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Sorry to be the bearer of bad news, but this is very unlikely.

Air Quality

Geothermal pockets produce Carbon Dioxide, and enough heat to melt ice. However, they also produce a large amount of sulfur dioxide (among other things), which is heavier than carbon dioxide. If the geothermal pocket sits in a valley, this would (slowly) fill the valley with sulfur dioxide and choke the plants of CO2. You would need to decide how the air is different in order to accommodate this.

Photosynthesis

Black Holes don't emit UV radiation. Stephen Hawking theorized (and through various tests it has been accepted by the scientific community) that Black holes do give off black body radiation, which unfortunately is within the Infra-red end of the spectrum, not the UV. This is called Hawking Radiation, as I see Tim Be II mentioned above. Plants as we know them couldn't photosynthesize.

Water

Geothermal pockets could produce enough heat to melt ice to provide water. However, they also produce a large amount of sulfur dioxide, which would quickly poison many, if not all, plants. The plants, however, could have evolved to tolerate the very acidic water.

Space

There is also an issue with space. The temperature change around a geothermal pocket is drastic within the vicinity of the vent. A cluster of vents could expand this heated area, but there would not be much room around the vent for plant life to grow. The change in type of plant would be drastic. Nearest the vent would grow tropical/desert like plants, and then temperate plants then tundra/coniferous plants, all within 5 and 50 meters of the vent. That isn't much room for a "jungle" to form.

Planet Issue

As for a ice planet orbiting a black hole, that would have to have either an extremely long year cycle, or and extremely low and fast orbit, both would have a significant effect on the planet.

In the former case, the planet's distance from the black hole would result in a core that cools very quickly and therefor geothermal pockets that cool down very quickly.

In the latter case, it would need to be close to its Rosch Limit, that way the tidal forces may cause enough tensile stress to cause friction and therefore keep the planet's core molten and the pockets warm, however there would be near constant earthquakes and a general environment not conducive to life.

There would almost certainly be bacterial life in those areas, but not complex life.

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    $\begingroup$ a blackbody emitter can emit any wavelength,, the peak frequency is given by 2.8 kT/h where k is the boltzmann constant, T is the thermodynamic temperature, and h is planck’s constant. You can totally have an ultraviolet black hole, it would just need to emit a lot of hawking radiation meaning you need a very small black hole. $\endgroup$ – taylor swift May 11 '18 at 13:41
  • $\begingroup$ What is the reasoning behind the Planet Issue section, if you don't mind elaborating more. I can't really see why the planet would require a vast orbit. A stellar mass black hole would gravitationally behave like a normal steller mass, so orbiting as close as Mercury wouldn't cause major issues. $\endgroup$ – abestrange May 11 '18 at 17:30
  • $\begingroup$ @taylorswift The problem is by the time your black hole is small enough to emit enough hawking radiation to warm a planet its lifespan is too short to allow life to form. $\endgroup$ – Schwern May 11 '18 at 23:10
  • $\begingroup$ @abestrange The size of the black hole would need to be sufficiently high t=so that it lasts long enough for complex life to evolve, so it would also dish out not enough Hawking Radiation, Schwern describes this brilliantly below, so i'll leave that to him. The internal friction heating concept would need the planet to be close to its Roche Limit, as the example in our system we know about is due to Europa being tidally locked to Jupiter and the effect Jupiter's other moons have on it, without those other close effectors the planet would need to be a lot closer to cause the same situation $\endgroup$ – Blade Wraith May 14 '18 at 13:19
  • $\begingroup$ @BladeWraith Ah thanks for pointing out that the intended source of heating was from Hawking Radiation. I had not yet heard of that being a possible option. I incorrectly assumed that you would rely on an accretion disk to provide the necessary radiation. $\endgroup$ – abestrange May 14 '18 at 15:54
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It is my understanding that a planet orbiting a black hole receives only light, and no heat...

This assumption is only for a non-feeding, non-rotating black hole. Stellar black holes (ie. they formed from a collapsing star) always rotate and, if there's a planetary system still around them after the collapse of the star, are often feeding.

Tidal Heating

Our hypothetical planet can get as close to the black hole as we like, so long as it stays outside the Roche Limit where it will be torn apart. As it orbits, it experiences tidal forces which tug on one side more than the other. The planet is literally stretched out. As it rotates, the direction the planet is stretched changes. This constant flexing produces tidal heating which provides heat to the planet. Europa, orbiting Jupiter, is such an example.

This would power your geothermal pockets.

Feeding

This is the simplest way to get energy out of a black hole, throw stuff into it. Thus the term "feeding".

As the matter stream spirals towards the black hole it forms an accretion disk around the black hole. Friction causes it to heat up and emit electromagnetic radiation: light. If the mass of the black hole is just right, the accretion disk can emit visible light.

Trouble is the black hole needs something to feed from. Usually this is another massive star, but there's no such star in your system. Nothing else is massive enough to provide energy on the time scales necessary to evolve life.

Hawking Radiation?

While black holes do emit radiation from Hawking Radiation, and it can be quite a bit, it doesn't emit enough of it consistently enough and for long enough for life to evolve.

The problem is the smaller the black hole the more Hawking Radiation it emits. Large black holes last a very long time, but emit very little radiation. Small black holes emit a lot more energy, but don't last long. By the time it's emitting enough energy to warm a planet it's smaller than the planet and won't last very long.

A 3 stellar mass black hole, the minimum needed to form a stellar black hole, would radiate 1e-29 W of power and last 6e68 years. This is an infinitesimal amount of power over an unfathomable period of time.

A 1e10 kg black hole emits 3.5 TW of power, but will only last 2.7 million years. That's a lot of power, but isn't enough to warm a planet. And 2.7 million years is a long time, but not in geological terms; it isn't long enough for life to form.

This is less massive than even a dwarf planet like Ceres by 10 orders of magnitude, so the black hole would be orbiting the planet (a pretty cool idea!)

Up the power to usable stellar levels and the lifespan gets shorter.

A black hole that emits as much energy as a dwarf star via Hawking Radiation is just 1e5 kg and will last 80 milliseconds.

Such a small black hole could not have formed naturally, it could only have come from a stellar mass black hole that's had 1e68 years to evaporate. So either your setting is in the Black Hole Era (which would be cool) or this tiny black hole is artificial.

How Did It Survive The Death Of A Star?

How did this planet wind up around a black hole? Typically black holes form from a massive collapsing star. Presumably this planet formed with the star and somehow survived the star's usually very energetic death without having all its lighter elements (ie. what makes up organic life) burned off.

If it was instead captured by the black hole it would have a very eccentric orbit taking it periodically very close to and then far away from the black hole producing an unstable climate unsuitable for sustaining life.

What Would A "Jungle" Look Like?

Not like the Rogue Planet on Enterprise where they can freely walk around in a warm Earth-like jungle. There's numerous problems with that.

There would be no atmosphere, even near the vents. Most of the planet would be too cold and the atmosphere would have long since frozen. The vents would heat the surface and produce gases, but it would quickly dissipate into the surrounding near-vacuum and freeze again. Without an atmosphere to conduct heat the vents would warm only a very, very small radius.

Another is the lack of light (visible or otherwise) for photosynthesis. You might instead have life forms optimized with high surface areas to absorb as much heat as possible from the vents, but without an atmosphere they couldn't get very far nor very complex.

More likely the planet would be like Europa with a thick sheet of surface (not necessarily water) ice. This would provide insulation for a core kept active by tidal heating. Below would be a liquid (again, not necessarily water) layer which could support life. The liquid layer would conduct heat and provide a stable environment for life to evolve.

There would be no "plants" because there's no light for photosynthesis. Instead it would look something more life around a deep sea hydro-thermal vent on Earth. Rather than photosynthetic organisms being at the bottom of the food chain, chemosynthetic organisms would be at the bottom of the food chain turning the chemicals and heat coming from the vents into energy.

You could get something akin to plants from organisms adapted to collect as much heat and chemicals as possible, such as giant tube worms. They would either be working in a symbiotic relationship with chemosynthetic organisms, as tube worms do, or have fully integrated them into their biology, like chloroplasts in plants.

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