10 or 100 Diameters of a Black Hole?

[RainOfSteel]

Ok, since Black Holes are supposed to be zero size points in space (last time I read, a long time ago), and given that they have titanic gravity fields, how do I determine the 10 and 100 Diameter distance thresholds for Jump safety from the black hole itself?

 

[Hecateus]

I don't think the 'rule of thumb' was intended to cover extreme densities. I can't seem to find the thread which discussed this.

But the Event Horizon would be a good basis...and on something that dense, I would say the minimum safe distance is a gazillion diamaters away.

Apparantly it is the Tidal effect that must be avoided when jumping...which makes me worry about gravity deck plating...or annoying jump drive hampering 'remote activated gravity-limpet mines' that pirates mights sneak aboard my ship when I am not looking.


[edit: > Here < is the thread...in plain site no less.

[edit2: reading further, the 10-100 seems to OTU be limited to conventional densities, gas clouds don't count. No mmention is officially made re Black holes.

 

[Anthony]

The tidal effect model is fairly simple, and basically works out to 100D * (density/standard planet density)^1/3. Assuming standard planet density is 5.0, that's 1.3 million km * (mass/Mearth)^1/3, or 0.6 AU * (mass/Msun)^1/3

 

[sandman]

Originally posted by Hecateus:
I don't think the 'rule of thumb' was intended to cover extreme densities.

Well, neither is Relativity

 

[Zutroi]

My suggestion would be to use the 100d limit for a main-sequence star with the black holes mass. This should fully account for any gravitational effects...

 

[Hecateus]

Zut, I am not sure that would have quite the same efffect. Radius expands linearly, but mass expands much more with the diameter of a main sequence star...ie Sirius is about 8 times the mass of Sol, but it's diameter isn't much more than Sol's. Black holes are often around that mass. But I seriously doubt that minimum safe distance is within the main sequence 10-100d limits.

Similar problem with main sequence Red Giants. Sol will eventually turn into a Red Giant. It's radius will expand and swallow the Earth...it will pretty much occupy the original 100d limit...but it's mass won't change until it starts to expell it's outer layers. Due to lowered density, it's tidal effct will also lessen. I wonder if it would be possible to jump inside such a star (assuming 100d limit is reimagined for tidal effect instead of diamaeter.)

 

[Andrew Boulton]

If you're close enough to a black hole to worry about this then YOU'RE TOO CLOSE!

 

[mark_rotteveel]

If you're close enough to a black hole to worry about this then YOU'RE TOO CLOSE!

I second that!

 

[RainOfSteel]

As for getting too close for the PC's own good, I was thinking about scientific expeditions and probes.

A mention of an adventure in another thread (The Traveller Adventure thread) with a black hole in it led me to thinking about some plot hooks, giving the PC's a job to study a black hole, or maybe supply or retrieve some scientists doing some studies there. Heh heh, not exactly at the top of desireable tasks, but if they're otherwise out of work or in trouble . . .

This led me to thinking about 10/100 G/J-Limit.

As I understand it, gravity isn't just a function of total mass, but, of course, how close you are to it. Sol is about 864,000 miles in diameter. So, the outer 100,000 mile shell exerts gravitational force that is much closer to any particular object outside the star than the inner 100,000 mile sphere (although relative density of the interior may give it more mass than the much more voluminous exterior shell; though I don't have the data to work that one out). This makes things very complicated, which is why I'm content to use diameters.

Black holes wrap up their entire contents into a single point, although, of course, stellar debris heading in toward a feeding black hole would excert their own gravitation pull, too.

I like Zutroi's comment about using the event horizon. It sounds like a game-plausive hand-wave that will avoid lots calculations that are beside the point for the role-playing.

Now I need to know how to figure out what the size of the event horizon of a black hole is.

 

[vegascat]

Another question for black holes is just how close can you get before high speed particles or Gamma radiation and larger chucks of whatever become a problem for ships and their crews? This would be a very unhealthy location for a ships crew to be. Heavy armor would not be of much help, and would be harder to decon afterwards.a black globe would be of some help, but how fast would it charge up the ships capacitors?

 

[TheEngineer]

Hi Travellers,

AFAIK you can calculate the event horizon -
often named as "Schwarzschild" radius by the
formula:
R = 2,95 km * (Mass of black hole / Mass of the sun)
So if our sun would be a black hole the Schwarzschild radius would be about 3 km.


Regarding the 10/100 diameter ranges just take
a look at the value g ratings in the appropriate
distances from the selected body.
You can use Newtons good old gravition formular:

a = 6,67e-11 x m / (D^2)
m is the mass of the body in kg
D is the distance in meters to the bodies mass centre

To get g - ratings just devide the result by 10m/s^2.

E.g.
At 10 diamaters from earth the acceleration is something around
0,027 m/s^2 --> 0,0028 g
At 100 diameters there are 0,0000280 g - not much - left.

So, if we have to deal with a black hole with a mass around 1000 suns the 10 diameter g-value
would be at a distance of 2200000000,
approximatly 15 au's (thats somewhere between Saturn and Uranus in our home system).

To be at a safe jump distance you will have to move to 147 au.

That pretty far away.....

I would suggest to set up an excel chart and
play around with black hole masses.

Besides, in galaxy M87 there seems to be a
monster of about 3 000 000 000 times sun mass.
Should be marked as a red zone, I guess.....

Dealing with vegascat last question....it depends
on how much traffic is there around the beast.
The space maybe cleaned up already.... there
is just everything inside of the black hole.

Or its still eating.
Then you can calculate the median speed of particles and chunks catched and accelerated
by black holes gravitation....
After a few days of "falling" even a micropiece
of dust will break every hull and overload
black globe capacitators...
Its not so very easy to calculate exactly because
of the changing gravitation, but if I have to...

Anyway its a great setting for a traveller adventure...

Regards,

Mert

 

[siefertma2]

Originally posted by vegascat:
Another question for black holes is just how close can you get before high speed particles or Gamma radiation and larger chucks of whatever become a problem for ships and their crews? This would be a very unhealthy location for a ships crew to be. Heavy armor would not be of much help, and would be harder to decon afterwards.a black globe would be of some help, but how fast would it charge up the ships capacitors?

Also, don't forget the whacky effects of time dialation. The closer you get to the nasty thing thhhheee ssssllloooowwwweeeerrrrr tttttiiiiimmmmeeee beeeecoooommmmeeeesss rrrreeeeellllaaaattttiiivvveee ttttoooo thhheee cccccccrrrrreeeeeeewwwww.

 

[vegascat]

Has anyone tried using a black hole in an adventure?
What problems did you encounter?

 

[TheEngineer]

I once made another "misjump setting" for my player group, kicking them out of jumpspace
at the g-well of a minor black hole.
Of course their humble merchant vessel was
nearly out of fuel.

One chance to get out was to reach a large gas giant placed a little bit nearer to the system center, which was already loosing hydrogen athmossphere to core direction.
Because of the weak maneuver drive they were
not able to do an easy skimming.

They had to calculate a keen route in order to
dive deeper in the gravity well of the hole,
do some classic turns around the giant.
Crossing the hydrogen area with high orbital
speed was quite a rough trip for both ship and crew.

Finally they changed to an more and more ecliptic orbit and with some help of engineering and DGP overthrust they made their way back to outer g well.

The seed was designed to get all the crew engaged with some action and their special profession.
Two of the players were students of physics, so
I had to calculate all the g stuff very carefully...

 

[MrMorden]

Originally posted by Rotters:
</font><blockquote>quote:</font><hr /> If you're close enough to a black hole to worry about this then YOU'RE TOO CLOSE!

I second that! </font>[/QUOTE]Agreed. Within 100 diameters of a black hole = DEAD.

 

[Pwyll]

Larry Niven wrote some really marvelous stories about black holes, if anyone is looking for inspiration