Can black hole be used in hardish science story?

[Czcibor]

After reading:

The Slate article was written by Phil Plait of Bad Astronomy, by the way.

Some of the points he mentions are:
-habitable planets around a black hole, with sunlight!
-a planet orbiting the black hole near the event horizon(way past the Roche limit)
-said planet having tidal waves(i.e., not being tidally locked)
-vastly egaggerated gravitational time dilation
-accretion disk being cold
-no spaghettification

I wondered about the following thing - is it possible to make a story in which there is a place for a habitable planet and a black hole? (I mean, I have one idea, but it does not end up well... ;) )

I see one additional limitation: the black hole was created in a supernova, so it would have not only exterminated nearby life, but also evaporated nearby planets. Any planet had to be formed later.

Black hole as far away accretion disk, which is barely visible on the sky? Boring... Any cool idea?

 

[Simon Bridge]

Planet orbits a bh+star binary.

 

[Czcibor]

Planet orbits a bh+star binary.

That's what I know, I more wondered what interesting stuff the black hole could provide when it's in safe distance.

 

[Khashishi]

To my knowledge, the larger the black hole, the lower the tidal forces will be near the event horizon, so for a sufficiently large black hole, all of that should be possible. I haven't run any numbers though...

 

[Simon Bridge]

Yep... look up super-massive black hole.

 

[DHF]

but there is a distinct problem with having a habitable planet around a black hole, mainly the fact that there would be no sunlight and therefore highly unlikely to have life.

 

[Simon Bridge]

The bh could have a non-black companion as mentioned above.
The accretion disk would probably be an issue, and life would need to be able to handle the radiation.

 

[Czcibor]

The bh could have a non-black companion as mentioned above.
The accretion disk would probably be an issue, and life would need to be able to handle the radiation.

That at least seems for me feasible:

Assuming that you have an equivalent of 10 km of Earth atmosphere, at the surface you should have:

10 000/150 = 66,(6) halving of amount of radiation.

So the surface goes 1/(1.17*10^20) of the radiation that was in the space. (Good enough or not?)

http://en.wikipedia.org/wiki/Radiation_protection#Shielding

Seems that the ozone layer would be massacred but the surface should be mostly intact. Yes, aquatic life or life very good ad shielding from UV.

The part that's tricky to me:
-how to put here any numbers (how far shall I place the black hole, to be both interesting and not outright lethal)
-it's not a stable main sequence star, but a black hole that produces light only during "feeding". Can I make it more or less stable? Or maybe the only realistic way is - whenever it devours another star then on the planet there is another mass extinction phase? While in hundred million mean time it is dormant, and can be only traced through gravitational lensing or its gravitational interaction with nearby stars?

 

[Simon Bridge]

You may want to look at Cygnus X1 for the srt of numbers to expect.
Youd want a more separated binary with a cooler star, but you don't want to rely on "feeding" for light.
A habitable planet would have to orbit well out of the accretion disk, and avoid the jets.
For gravitational effects... anything noticeable would probably be fatal as well.

 

[DHF]

so I am curious. If we are talking about a Binary system with a cooler star and a black hole, The planet in question would have to be a considerable distance from the black hole to avoid the extreme gravity and radiation, would the light from the star be enough to benefit the planet at all considering the distance?