Black Holes

[Blue Ghost]

We've talked about black holes in Traveller in the stellar mass thread, but we've never had a thread dedicated to them.

VSauce gives some of the basics on Black Holes;

https://www.youtube.com/watch?v=3pAnRKD4raY

And SciShow Space does the same;

https://www.youtube.com/watch?v=L8GCR88T3fE

https://www.youtube.com/watch?v=kq4u7Sv7GT4

List 25 gives their take;

https://www.youtube.com/watch?v=ZvAsvLjEdIo

 

[aramis]

To prevent an object at C from escaping, it needs to decellerate it by 300,000,000m/s...
or about 3e8 Gees. For 10 solarmasses, hyperphysics calculates a schwarzschild radius of just a bit under 30km. 0.0001LS. At 8.4 LM, that's 8.4*60*10000 times the distance... 5 million times the distance. or 1/25000000000000 the G's. You should be safe at 1 AU if it isn't "feeding"...

If it's feeding... well, the energy dump of a feeding black hole exceeds that of many stars... be a bit... warm.

 

[WistfulD]

Which highlights the often neglected fact that black holes are not cosmic vacuum cleaners. Unless you're in a position where you'd be in danger of falling into a star of the same mass, you're not in emmediate danger from a black hole (the likelihood of getting hit by a mass ejection, however, still means that you shouldn't get close, plus the fact that why would you?).

 

[Blue Ghost]

Yeah, that's been an issue niggling at the back of my mind. I think a lot of physicist have "Trek engineering / TL" in mind when they talk about the event horizon, and how you can't escape at that point.

Well, if you're close enough to get to the event horizon, then I got news for you, unless you have some very high tech under your hood, your epitaph was written way long before you got that close.

I am somewhat puzzled (perhaps even bothered) by something though, and this just stems from my absolute ignorance on the subject, but I've seen references that black holes can be destroyed by radiation. I'm assuming they mean high energy particle radiation. Given the nature of what black holes are, and given that space is filled with radiation given off by stars, how is it that black holes even survive as they are today?

My blind stab at an answer tells me that black holes, if susceptible to radiation, then it's got to be one of the radiation particles (Alpha, Beta, Gamma.......I can't remember the others from my university physic's class).

I'll have to do some research.

 

[aramis]

I am somewhat puzzled (perhaps even bothered) by something though, and this just stems from my absolute ignorance on the subject, but I've seen references that black holes can be destroyed by radiation. I'm assuming they mean high energy particle radiation. Given the nature of what black holes are, and given that space is filled with radiation given off by stars, how is it that black holes even survive as they are today?.

it is that they radiate away. Infalling radiation simply adds mass. they radiate very slightly.

 

[tjoneslo]

I am somewhat puzzled (perhaps even bothered) by something though, and this just stems from my absolute ignorance on the subject, but I've seen references that black holes can be destroyed by radiation. I'm assuming they mean high energy particle radiation. Given the nature of what black holes are, and given that space is filled with radiation given off by stars, how is it that black holes even survive as they are today?

The term you want to search for is "Hawking Radiation".

It arises because there are pairs of particles created (and immediately destroyed) in bare vacuum. But on the edge of the event horizon of a black hole, one of the two particles gets gobbled up by the black hole, and the other escapes into the void. In order not to violate the second law of thermodynamics, the physics of where the energy came from to create the new particle is the black hole itself. So eventually every black hole will evaporate into a cloud of radiation. But the time scale for a stellar sized black hole to evaporate is longer than the current age of the universe.

 

[Blue Ghost]

Interesting. Coming up with story / adventure concepts here.

 

[Frankymole]

Which highlights the often neglected fact that black holes are not cosmic vacuum cleaners. Unless you're in a position where you'd be in danger of falling into a star of the same mass, you're not in emmediate danger from a black hole (the likelihood of getting hit by a mass ejection, however, still means that you shouldn't get close, plus the fact that why would you?).

This is what amused me about the "Doctor Who" episode "The Impossible Planet", all about a planetoid that was orbiting a black hole whilst loads of other material was passing by and getting gobbled up. Why shouldn't it be orbiting? "Impossible" in the sense of "perfectly possible and indeed likely that something could orbit a mass in space".

 

[Blue Ghost]

But what sort of radiation would they be experiencing?

I wrote a teaser in the TAS news section I think, about a planet that started gushing plasma at the poles, as if there might be a black hole at the center *insert creepy 1950s theramin space music here*

The concept there being that it was an artificial planet (possibly a Grandfather construct) with a reactor at the core that used a controlled and contained spinning black hole. I never finished the concept beyond the teaser ... even though I posted it here, and it now belongs to Avery and the COTI, I may try to write up wholly and finish it.

But I digress; I do wonder what it would be like to live on a "class M" planet that somehow could survive the radiation of a black whole. Or, even more interesting, if it was a binary system with a regular star and black hole feeding off of it, and some planets orbiting both.

I may write this up too.

 

[aramis]

This is what amused me about the "Doctor Who" episode "The Impossible Planet", all about a planetoid that was orbiting a black hole whilst loads of other material was passing by and getting gobbled up. Why shouldn't it be orbiting? "Impossible" in the sense of "perfectly possible and indeed likely that something could orbit a mass in space".

It shouldn't have survived the supernova.

If it wasn't vaporized initially in the flash, it was pushed out of orbit by the gas-shell in the detonation, where it is likely to be above stable orbital velocity.

Further still, the supernova (before collapse) sheds a LOT of mass - and thus reduces the stable orbit speed.

So, it's been pushed out, and is now orbiting a smaller mass, and is likely to be at escape velocity.

And then the accretion begins... as matter and energy† fall into it, it gains mass, needed orbital velocity increases, and anything in a stable orbit begins to fall inward due to insufficient orbital speed. As it falls in, the difference between its orbital speed and its needed stable orbital speed widens... and so it falls in faster and faster.

Plus, anything that happens to be falling in has both gravitational drag and potential to impact.

So, really, the planet orbiting would be most unlikely to be falling in at the right angle of incidence and the right velocity to become stable, and even if it does, it won't remain stable as more falls into the black hole.


†Remember: Energy has a functional mass, and unlike a normal body, the energy cannot escape the black hole.

 

[G. Kashkanun Anderson]

It shouldn't have survived the supernova.

It needn't have been a survivor of the original system; it's debatable whether stars big enough to form black holes are decent candidates for planetary systems to begin with.

Rather, a planet orbiting within spitting distance of a black hole is probably something reassembled from the debris left behind after the supernova event -- or, perhaps even more likely, from the scattered remains of a cataclysmic merging of two neutron stars.

A massive enough Jovian or brown dwarf in a sufficiently distant orbit might be able to survive a supernova as a terrestrial core, though, as could a Jupiter-mass terrestrial world, if such exist (theorized, but not proved).

 

[aramis]

It needn't have been a survivor of the original system; it's debatable whether stars big enough to form black holes are decent candidates for planetary systems to begin with.

Rather, a planet orbiting within spitting distance of a black hole is probably something reassembled from the debris left behind after the supernova event -- or, perhaps even more likely, from the scattered remains of a cataclysmic merging of two neutron stars.

A massive enough Jovian or brown dwarf in a sufficiently distant orbit might be able to survive a supernova as a terrestrial core, though, as could a Jupiter-mass terrestrial world, if such exist (theorized, but not proved).

And it's not in a stable orbit, as the gravity continues to climb over time.

 

[salochin999]

A planet orbiting a black hole sounds like the perfect setting for a horror themed Traveller game.

 

[Blue Ghost]

I don't think you'd need any extraneous supernatural stuff. I think if you were in a vacc suit standing next to your ship on an airless barren planet, staring at this jet-black thing silhouetted by light, sucking in mass from a star, you'd be crazy not to be scared. o:

 

[WistfulD]

But what sort of radiation would they be experiencing?

I wrote a teaser in the TAS news section I think, about a planet that started gushing plasma at the poles, as if there might be a black hole at the center *insert creepy 1950s theramin space music here*

The concept there being that it was an artificial planet (possibly a Grandfather construct) with a reactor at the core that used a controlled and contained spinning black hole. I never finished the concept beyond the teaser ... even though I posted it here, and it now belongs to Avery and the COTI, I may try to write up wholly and finish it.

But I digress; I do wonder what it would be like to live on a "class M" planet that somehow could survive the radiation of a black whole. Or, even more interesting, if it was a binary system with a regular star and black hole feeding off of it, and some planets orbiting both.

I may write this up too.

Hawking radiation would be electromagnetic radiation is a black body with a temperature inversely proportional to the black hole's mass.

Matter falling into an event horizon, however, tends to give off gamma radiation and other high-energy particles, so there can be your plasma gush.

The smaller a black hole is, the more quickly it evaporates. David Brin's Earth, for instance, speaks of a microscopic black hole in the Earth's mantle that was so small, at certain densities in the Earth, it was evaporating as quickly as it was consuming matter (smaller size = more evaporation AND less likely to run into a particle).

 

[flykiller]

the energy dump of a feeding black hole exceeds that of many stars

like to see what happens if these two merge ....

http://phys.org/news/2014-10-composite-image-black-holes-orbiting.html

 

[Lycanorukke]

Well, if you're close enough to get to the event horizon, then I got news for you, unless you have some very high tech under your hood, your epitaph was written way long before you got that close.

That's one of the more interesting things with certain types of black holes. In the case of supermassive black holes, the tidal forces don't get to the point of tearing you apart torn apart until you are well inside the event horizon (you're still not getting out again without treknobabble though).

Another fun one are 'primordial' black holes. Not formed by stars but formed by mass concentrations at the beginning of the universe. As such they can be any size - though due to Hawking radiation, evaporation the smallest left today is calculated to be about 10¹¹ kg (microscopic in size).

Now if you want a small "asteroid sized" black hole (horizion radius 100m) the mass is about 4.5 x 10²⁹ kg (roughly the same as Barnard's star). So you could technically have planets happily orbiting the hole at the same distance as any other red dwarf without a supernova blowing them to bits. Though of course the hole would have had to have grabbed/stolen the planets from somewhere else.

 

[Blue Ghost]

Interesting.

But I'm more addressing any hope of escaping the hole via starship thrust at the most common tech levels, apart from actually feeling the effect of being stretched and crushed like a cartoon character.

At sufficiently high enough tech levels, it may be possible to negate the spaghettification effect, and travel to the heart to experience the mass of subatomic particles, or whatever is there. That would prove a most interesting adventure.

 

[WistfulD]

Well, gravity manipulation technology and FTL drives can pretty much act as magic wands in this case. The event horizon is quite literally only important if the speed of light is, and a black hole is only a threat to you if gravity is. Therefore, the two most game-intrinsic violations of known physical laws pretty much disrupt everything scary about black holes... if the GM says that they work in that instance.

 

[whulorigan]

Well, gravity manipulation technology and FTL drives can pretty much act as magic wands in this case. The event horizon is quite literally only important if the speed of light is, and a black hole is only a threat to you if gravity is. Therefore, the two most game-intrinsic violations of known physical laws pretty much disrupt everything scary about black holes... if the GM says that they work in that instance.

Yes, but I think I would have to argue that the game-descriptions for gravitics/contra-gravity and/or any given FTL-Drive are specific to their operations under normal space-time conditions (relatively speaking). Close to an Event Horizon surface, I would think that the physics of their operation would be a more complex relationship (speaking intuitively from a make-believe science standpoint, of course ).