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PostPosted: Wed May 17, 2017 3:50 pm 
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Is it possible to have extant planetary systems around a black hole?

If I remember correctly, you need an O-type, or at least a fat A-type, to have enough mass to collapse into a black hole. Because of the intense and energetic radiation, the local disk is likely to be swept clear of dust and debris out to the Oort Cloud. Then, when the star goes into giant phase and then novas, the shockwave would clear out anything that was nearby anyway.

I'm putting together a scenario where a jovian (now cthonic) with habitable (sorta) moons is around a black hole, but I've gotten the feeling recently that it crosses the line from "infintesimal, but non-zero" to "no, this is fantasy". Note: I can work with that, but I do want to know what foundation I'm building on.

What do you think?


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PostPosted: Thu May 18, 2017 3:13 am 
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It'd be pretty unlikely, I think. First you need a big star as you pointed out - O type, maybe a high mass B, but not an A or less though. Those have short lifespans on the order of a few million years, and tend to blow away their protostellar disks pretty rapidly anyway. And then they turn into supergiants and blow up as supernovae.

Some neutron stars in nebulae do have planets around them (the infamous "pulsar planets"), and one explanation for those is that planets might be able to form out of the debris after the explosion, but I can't think of any black holes that are in supernova nebulae (a search doesn't reveal any either - have we just never found any?). If they do exist then maybe you can get planets forming around them like they allegedly do around neutron stars.

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PostPosted: Fri May 19, 2017 1:15 pm 
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Perhaps if the gas giant originally orbited a different star, but was captured by the black hole when its parent star came too close to it?

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PostPosted: Sat May 20, 2017 4:30 am 
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Baron Opal wrote:
I'm putting together a scenario where a jovian (now cthonic) with habitable (sorta) moons is around a black hole

What warms the moons?

Also, if the gas giant has lost most of its mass in becoming a chthonian, will the moons still be gravitationally bound?

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PostPosted: Sat May 20, 2017 2:19 pm 
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From what I understand of the gravitational issues, as the mass decreases, so does the hill sphere radius. However this also depends upon distance. In general, the further from a star a planet is, the larger its gravitational influence becomes, thus increasing its hill sphere radius. In order for this Jovian's moons to continue orbiting about it, it must have been at the edges of its solar system, where its hill sphere influence would be largest. Even if the mass were to decrease, the distance from the black hole should compensate and allow the moons to continue orbiting about the planet.

Now, will these moons be habitable? Tidal flexing could warm the moons, just like what happens with the Galilean satellites of Jupiter. If the moon is rocky, it's unlikely to be able to support life as it would end up being volcanic like Io. If on the other hand the moon were like Europa, tidal flexing from the Jovian could warm the interior of the planet and create a subsurface ocean that could support a form of life. Any light however would have to come from bio-luminescence. It certainly wouldn't come from the black hole.

The other thing is if the beings on these moons were technologically advanced when the star collapsed into a black hole. How much of their civilization would manage to survive the catastrophe?

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PostPosted: Sat May 20, 2017 9:29 pm 
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Well, it was a bit of a winding road.

The thought was that it is a planet orbiting a black hole. I'm trying to come up with a scenario where that is possible, if not feasible. After the conversion, the back third of the planet is not sterilized and life survives. I haven't decided yet that it's the original civilization, colonized ruins, or newly evolved. Then, I thought it might have to be a jovian moon to give the planet more shielding from the blast. Would the jovian be cthonic at that point?

The inhabitants look up in the sky at the Sol Adligatus, farm their black and purple flora, and retreat to the Final Enclave before the critters come out.


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PostPosted: Sun May 21, 2017 12:01 am 
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The reality of the situation is that reality tends to break down around a black hole. Now, there's nothing that says in a science fiction setting you can't have a world's population surviving a major cataclysm that would have otherwise rendered all life extinct. Star Trek: Enterprise did it with the planet Dakala, a class R world ejected from its system and left to wander the cosmos alone. Ordinarily, such a world would have completely frozen over and all inhabitants would have died, but Dakala was found to have both an atmosphere and life forms due to geothermal venting.

So in a science fiction setting, you can have a Jovian moon and a portion of its inhabitants survive the cataclysm that turned the parent star into a black hole. You can even provide plausible scientific reasoning for it (e.g. the discussion regarding hill sphere radii and tidal flexing). But here's the reality: stars with sufficient mass to collapse into a black hole are too large and too short-lived to create planets. If planets did somehow form, they wouldn't be habitable, simply because there would be no time for evolution to do its work before the star exhausted its fuel. When the star collapses into the black hole, it would start taking in all the matter it could find, including planets. There would be no survivors.

You might be better off going the Dakala route and having the world be a rogue.

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PostPosted: Sun May 21, 2017 5:58 am 
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Baron Opal wrote:
Well, it was a bit of a winding road.

The thought was that it is a planet orbiting a black hole. I'm trying to come up with a scenario where that is possible, if not feasible.


Feasible? Or likely?

Quote:
After the conversion, the back third of the planet is not sterilized and life survives. I haven't decided yet that it's the original civilization, colonized ruins, or newly evolved. Then, I thought it might have to be a jovian moon to give the planet more shielding from the blast. Would the jovian be cthonic at that point?


If it is the moon is airless, too.

Quote:
The inhabitants look up in the sky at the Sol Adligatus, farm their black and purple flora


This black and purple flora is chemosynthetic, I suppose, as it grows in complete darkness.

These inhabitants — how did they survive being inside a supernova? Or did they evolve later on an airless, waterless moon?

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PostPosted: Sun May 21, 2017 6:20 am 
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Traveller wrote:
When the star collapses into the black hole, it would start taking in all the matter it could find, including planets.

It'll only take in planets etc. if there is some mechanism that removes their orbital energy and angular momentum. And that's no more likely for planets orbiting a black hole than for planets orbiting a star.

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PostPosted: Sun May 21, 2017 5:32 pm 
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Agemegos wrote:
Feasible? Or likely?

Well, informally they're the same thing. "Feasible" does sound better to the ear since I'm crafting the system, however.
Quote:
Baron Opal wrote:
The inhabitants look up in the sky at the Sol Adligatus, farm their black and purple flora

This black and purple flora is chemosynthetic, I suppose, as it grows in complete darkness.


Photosynthetic. I was imagining that there would be plenty of UV from the black hole from infalling matter. (Where did the accretion disk come from? I don't know. That's a step further down that I've gotten, yet.) The thylakoids in the chloroplasts would appear black if they absorbed those particular wavelengths.

Quote:
These inhabitants — how did they survive being inside a supernova? Or did they evolve later on an airless, waterless moon?

Thus hiding the planet / moon behind the jovian. Also accepting that a good portion of the atmo- and hydrospheres would be eliminated. But, only one city of 10,000 would need to survive. (c.f. Toba) I'm also picturing that the planet needs to survive a blast wave and not a prolonged baking, which may be incorrect.

It may be that I'll need to have the black hole be wandering and captured by the system. Which will have unfortunate consequences for the original star.


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