Balck Holes too soft - Page 4

Suicide Junkie · #31 March 31st, 2001, 02:01 AM

quote:
Here is a question for you--could our sun become a black hole?

Yes. Even Earth would become a black hole if you squeezed it down to the size of a marble (1 cm)
Will it happen naturally? Not a chance.

quote:
A black hole has a huge mass right? So if a ship tried to orbit it, would it take lots of energy to remain in orbit?

To remain in orbit takes zero energy. Just take a look at the sun/earth/moon.

It may take a lot of energy to get into orbit from the surface, but once you're there you're there for good until you hit something, or generate thrust.

quote:
1. A spacecraft the size of the shuttle approaches our sun on a course aimed directly for the 'center' of the star.
2. Take the main engines used to achieve escape velocity out of the equation.
3. Assume the spacecraft doesn't use any fuel until it reaches closest approach.
4. Assume that heat/radiation aren't a factor--robotic pilot if you want.
How close do you think the spacecraft can get to our sun before it must alter its course to try to enter an orbit around the star?

The key to getting an orbit is to have a mass whose gravitational well you happen to be in.
The Intrepid Space Pilot in your question happens to be in an orbit already, its just that that orbit happens to pass through the surface of the star

In order to stay in orbit, all the spacecraft must do is miss the star. To do that, the spacecraft need only dodge sideways one star-radius. It will then skim past the edge & go flying out, slow, fall back, and zing past the opposite edge.

Now, lets say you want to orbit an object that's 30,000Km wide. Since we are heading straight for it at the moment we must move sideways 15,000Km before we hit. If our ship is one second from impact, we must accelerate to 0.1c (10% the speed of light) in one second, then we can cut engines and be in orbit.
By accelerating to 30,000Km, in one second, we average 15,000Km/s, and in the one second before we hit, we've slid one star radius to the side, and fly past.

If we are nice and far away, such as near pluto's orbit, then we will have weeks to months before we reach the (30,000Km)"sun" (light takes 7 hours to get to pluto, and we're not going to be going anywhere near lightspeed)
divide the 15,000Km by 2 months, and we have:

quote:
No-calculator math time:
2 months= 60 days
=60*24 = 1200+240 = 1440 hours
=1500 x 60 = 60000+3000 minutes
=60000 x 60 = 3,600,000 seconds
15,000km / 3,600,000 seconds
=15 km / 3,600 s
= 15 /3.6 m/s
= about 5 m/s
= Jogging Speed.

So, even a ship without engines coud merely open a door & vent some atmosphere, to get a boost to that speed.

All you have to do is scoot sideways the width of your target & you're in orbit. Very Hot & Very cold at times, but an orbit nonetheless.

raynor · #32 March 31st, 2001, 04:02 AM

Thanks!

Stupid Sci-Fi shows should try to be a bit more accurate about black holes.

AJC · #33 March 31st, 2001, 05:37 AM

Excellent SCI-FI book -

Light of Other days
by Arthur C. Clarke, Stephen Baxter http://images.amazon.com/images/P/08...1.LZZZZZZZ.jpg
Its about wormholes. Fascinating read.

[This message has been edited by AJC (edited 31 March 2001).]

jc173 · #34 March 31st, 2001, 10:57 AM

Sheesh next time I need a lesson in orbital mechanics for a sci-fi roleplaying game or a piece of fan fic, I'll remember to ask here. <G>

dogscoff · #35 April 2nd, 2001, 02:01 PM

<Red Dwarf>
Thing about space, right, is it's black. And the thing about black holes, right, is they're black. So how you meaent to see 'em then?
</Red dwarf>

Sorry, it was all getting beyond me=-)

------------------
--
There is an exception to every rule. Including this one.

raynor · #36 April 2nd, 2001, 04:27 PM

I just watches four episodes of Star Blazers yesterday. Their mission is to travel around 200,000 light years in less than a year. That's a pretty good distance considering that ST:V'Gr is gonna take around 70 years to travel just 70,000. Oh, I just figured it out. They made their first space warp from the moon to Mars and covered several thousand light years. :-)

Sirkit · #37 April 2nd, 2001, 06:02 PM

black holes are tecnically a pain in the *** to detect, but in the case of light if matter was caught in the accreation disc you could see it and then recognize the fact that a dense peiec of matter was at the center (ie. a black hole) BTW listen to Suicide_Junkie for the most part hes right

Suicide Junkie · #38 April 2nd, 2001, 08:36 PM

quote:
Their mission is to travel around 200,000 light years in less than a year.

I hope that wasn't a straight line distance.
Since [our] galaxy is only 100k LY across, that would put them in the middle of nowhere no matter which way they went.

--------------------------------

Black hole detection:
If your black hole didn't have an accretion disk, and there was nothing in orbit (or even nearby), then it would be difficult to see indeed.
There would be a slight distortion from gravitational lensing around the edge of the hole, but you'd have to be looking right at it.
The ship would be slightly stressed from gravitational shear, but it it was noticeable over the air & people inside, it would be too late anyways...

But the main thing is:
This black hole is in the middle of nowhere, since there is nothing in the area to form an accretion disk. That means you'd have no reason for going there in the first place, & would never be in that position.

If you were travelling through an SE4 warp point to get to a BH system, then you'd have something to compare your movement to.
Since the WP is at a fixed distance from the hole, and likely provides no momentum to your ship, you would immediately start falling towards the hole.
What you would see is the WP moving away from you.
So, you:
A) full thrust for the WP & go home right away.
B) Assume you're being pulled by gravity & not an alien tractor beam, so you thrust sideways and go into orbit.
From your orbit & seeing the motion of the stars, you figure out where the hole is & what its mass is. Having mapped the system, you look for other WPs and then report to the empire for further instructions.
Note that the orbiting of the hole is easy & immediate.

quote:
Black holes are tecnically a pain in the *** to detect,

Well, Black holes are a pain to detect, sitting on your home planet if you're flying around in your spaceship inside the BH system, and have a WP to compare to, its mindless busywork to detect and map the thing.

[This message has been edited by suicide_junkie (edited 02 April 2001).]

Nitram Draw · #39 April 2nd, 2001, 08:41 PM

I thought they found black holes by looking for what was not there, no light where there should be some. I know they use x-rays and heat measurements also but I thought the absence of light was the main indicator.

Suicide Junkie · #40 April 2nd, 2001, 11:30 PM

quote:
I thought they found black holes by looking for what was not there, no light where there should be some. I know they use x-rays and heat measurements also but I thought the absence of light was the main indicator.

Very good.
the point you're missing is that they knew something is there, just not what it could be. If you look out into the depths of space at a black hole, you don't see much at all, and move on. If you see a star going in little circles, but nothing else, then you look closer and find that theres got to be a star-sized mass right there, but we don't see any light. Probably a black hole.

If the hole is sitting all alone, then it is almost impossible to detect. When your ship goes through the warp point, the hole is no longer alone, you and the warp point are there, & you can quickly see somethings amiss and conclude that it's a Black hole