Black hole
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Basic Information

A black hole is an astronomical body whose gravitational pull is so strong that even light will be permanently drawn in if it comes within a certain distance. The escape velocity of the black hole is greater than the speed of light. The light (or any object traveling at or very close to the speed of light) either enters an orbit around the black hole, or gets "sucked in", depending on the direction the light was traveling relative to the black hole.

Any matter that crosses this orbital threshold, known as the event horizon, will be torn apart into elementary particles and irrevocably lost. Since light cannot escape, black holes cannot be seen directly but must instead be inferred from the effect they have on their surroundings. General relativity predicts that all of the mass of a black hole is concentrated in a single mathematical point, called a singularity.

The concept of a star so massive that it's own light could not escape was first proposed by John Michell in 1783, but at the time it was such an outlandish concept that the scientific community failed to embrace it. In 1916, physicist Karl Schwarzchild discovered that Albert Einstein's Theory of Relativity had solutions that allowed for light to get stuck in an orbit or collapse into a "hole" in spacetime. Over the decades that have since passed, the scientific consensus has gradually shifted to accepting that Black Holes almost certainly exist within our Universe.

A black hole is created if a mass if compressed to within its Schwarzschild Radius $\left(r_s=\frac{2Gm}{c^2}\right)$, which will also determine its event horizon. For the Earth, that would mean compressing it to the size of a peanut. However, it is predicted that a sufficiently massive star will go through a gravitational collapse to within its Schwarzschild radius after it burns out. Michell's math suggested it would take a star 500 times as massive as our sun, but more recent work suggests it's a possible end-stage for a star just 10 to 50 times the mass of our sun. Point being, most black holes are actually going to be much smaller than you might imagine. After all, they are collapsed stars. What's special about them isn't the amount of mass they have, it's that this mass is compacted into a very tiny area. If a star the size of our sun managed to collapse to the point of being a black hole, its event horizon would only be about 6 km in diameter.

Black Holes cannot currently be directly observed, since they swallow up the light and radiation we would use to see them. It would be possible to detect distortions where light is bent by some unseen object of great mass. Determining whether such a distortion was from a genuine black hole, as opposed to distortion caused by a Massive Compact Halo Object or other hypothetical form of Dark Matter would probably be difficult and dangerous. As such, a Black Hole might serve as a navigational hazard in a role-playing game.

Flying Into A Black Hole

In most settings, we can assume there will be some way of detecting and avoiding a black hole. Established space lanes and commonly traveled routes will avoid black holes and suspected black holes. The ships' computer might analyze visual data from the sensors, compare them to star charts, and compute likely gravitational distortions in the vicinity. With superscience or applied phlebotinum you might be able to build a sensor that accurately detects the warping of spacetime that occurs near a black hole.

So, black holes should really only be a danger to vessels exploring remote areas of space, or to ships that for whatever reason have lost their navigational sensors, computers, or star charts. For the sake of drama, though, we'll assume you've somehow bumbled upon a black hole without warning. It's not going to look like a big area of darkness as you might expect, at least not until you get very close. Instead, light from objects far beyond it will be bent, so you'll actually see behind the black hole. Objects on the other side of it will be distorted, but if they're just distant stars the distortions might not be immediately obvious. At near ranges to the event horizon, you'd be able to notice the big black spot, but the relativistic speeds used by most fictional space propulsion systems may well mean you have very little time to react.

At the Event Horizon, light is in orbit. As you cross that horizon, if you look perpendicular to your motion, you'll see light that has circled around. If the Schwarzschild Radius is small enough, you may actually see yourself in the distance, or even a chain of yourselves, as light runs circuits around similar to what happens on a hypersphere. Of course, if the black hole is large, the diameter of the event horizon may be so long that you and your spacecraft are tiny specks. One dramatic element the GM could narrate in would be the ship's automated proximity alarm going off, as the computer suddenly detects several other ships. This phenomena would alert you to the fact that you'd reached the Event Horizon, but it'd be too late to escape unless you have an FTL Stardrive. Unless you can travel Faster Than Light, the best you could do at this point is establish an orbit of the black hole. Again, the likely speed your craft was traveling at, and the relatively narrow band of the event horizon, means you're not likely to be in the orbital plane for long.

As your orbit decays and you fall into the black hole, things start getting distorted. This is going to be a nightmare, but at least you won't be staring a multiples of yourself any more. You'll be stretched in the direction of the black hole, and squished in the directions perpendicular to that. The parts of you closer to the singularity will feel much greater gravity, and start falling inward faster than the parts of you that are further from it. This stretching is called "spaghettification", but it'll actually look more like what happens when you stretch a broken rubber band. As you get longer, your midsection gets thinner.

Objects closer to, or further from, the singularity would get dimmer, and the light coming from those directions would have a reddish tone. This is the result of red shift, the phenomenon of the light taking longer to reach you. Looking perpendicular to your velocity, everything would be brighter, and have a slight bluish tone. This is the result of blue shift, the phenomenon of light taking less time to reach you. Your view would become distorted to include more of the plane perpendicular to the radius of the black hole, and our binocular vision would have serious trouble interpreting the distorted space. It would appear that the universe had been flattened into a plane perpendicular to your motion. These distortions would eventually become so strong that you would die, and then be crushed into the singularity. You'd be ripped apart on one axis, and crushed on the others.

Time would dilated as you accelerate into the black hole, but you'd be unable to notice. If your spacecraft were very large, you might be able to notice things ahead of you slowing down and stretching. It probably depends on the size of your ship, the size of the black hole, and the speed of your approach.

An outside observer watching your approach on the Schwarzschild Radius would see a very interesting display, though. First, you'd start to fade - this is the redshift effect again, as light coming from you takes longer to travel the distance to them. You'd appear to stretch. Your travel toward the center of the black hole would speed up, but the dilation of time would mess up their perception of it, and your other motions would seem to slow down. Eventually, as you cross the event horizon, you'd vanish from sight completely, as the light bouncing off of you would get stuck on that side of the Event Horizon.

Tropes over science

It's extremely rare that TV or movies depict a black hole at all realistically.
Gravity Sucks
Space Does Not Work That Way
Unrealistic Black Hole
You Fail Astronomy Forever

Sources

Bibliography
6. Non-Fiction Book: Hyperspace by Michio Kaku
7. Curious About Astronomy - page on the size of black holes

Game and Story Use

• A black hole may actually be one side of a wormhole, leading to any other place in space and/or time, or even to a different dimension or parallel universe. Of course, there's the matter of creating a wide enough opening and of somehow passing through without being utterly destroyed in the process.
• Also, this is probably a one-way trip, and with no idea what's on the other side.
• Your best odds of surviving entry into a blackhole-wormhole are if its a rotating black hole. See that entry for more details.
• Related theories:
• White Hole a mirror of the black hole which can theoretically exist paired up with a black hole.
• Fecund Universes theory - suggests everytime a black hole is formed, it creates a new universe within it.
• The sheer mass of a typical black hole makes its gravitational pull so strong that spaceships cannot safely go anywhere near it. Thus, a well-placed black hole can be an important strategic factor.
• The ability to create black holes can make for an impressive weapon. These can run the range from cannons firing micro-black holes that dissipate soon after taking a chunk out of enemy ships to planet- or system destroying weapons.
• If used carelessly or ruthlessly, such weapons can cause collateral damage on an unimaginable scale.
• A doomsday cult may try to cause the end of the world by creating an artificial black hole.
• A spacefaring civilization may use a black hole as a dump site.
• If it's actually one end of a wormhole, this may generate some unwanted attention…
page revision: 17, last edited: 19 Aug 2009 22:20