Transwiki:Black hole FAQ
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[edit] Black Hole FAQ
Here are some frequently asked questions on black holes, the strangest objects in the sky.
1. Q. What is a black hole?
A. A black hole is a region is space with so much gravitational attraction that nothing, not even light can escape.
2. Q. Will black holes suck up everything in the universe?
A. No, black holes have an area around them called an event horizon. Once you go pass this horizon you'll get sucked up, but as long as you are out of the event horizon you are safe.
3. Q. How come we can't see a black hole?
A. No light emits out of a black hole and if there is any light emitting out of the black hole it gets sucked right back into the black hole so it never reaches our eyes.
4. Q. What would happen if I got sucked into a black hole?
A. You will be pulled long and thin due to the gravitational tidal forces from the black hole. Then you'll be squeezed into an extremely small space called a singularity.
5. Q. What is a black hole's effect on time?
A. General relativity (A theory proposed by Albert Einstein, that states how matter creates gravitational force by distorting the very fabric of spacetime and how matter reacts to the shape of spacetime.) predicts that when an object approaches close enough to a black hole, it's infall rate will slow down as seen from far away. Also, any signal from the object show that clocks are running more slowly than of ours. This difference is called time dilation.
6. Q. Can a black hole transport a Human being to one place to another?
A. Science fiction supports such objects called wormholes that transport you to one spot in spacetime to another spot. Transporting beings through a black hole is pretty much impossible. First, you wouldn't survive the fall into a black hole, so there is no use in transporting people by this means. Second, cosmic censorship states that no object that enters a body with a singularity (such as a black hole) can escape.
Different types of black holes have differently shaped singularities: in a stationary black hole it is a point, in a rotating black hole it is a ring. If you passed through the center of the ring without touching the ring singularity itself, the mathematics predicts you will come out somewhere else and you cannot return. This is the basis of the wormhole idea. However the mathematics gives no indication of where (or when) that somewhere else is, and no way to control or select it yourself.
7. Q. Do black holes last forever?
A. No, black holes evaporate by a process called virtual particle production (see Hawking Radiation). In this process a particle pairs up with it's antiparticle at the event horizon. Normally particles and antiparticles destroy each other on contact, but in this case the black hole rips the particle and antiparticle apart before they can annihilate each other. One of these particles fly off into space and the other falls into the black hole. Since the one of the black holes particles have just been lost, the black hole has lost mass, and since this is happening all the time black holes are always losing mass.
8. Q. Will the sun turn into a Black Hole?
A. No, the sun is not massive enough. If it was 10 times as massive as it is now it would.
9. Q. If the sun did turn into a Black Hole what would it's effect on our Earth be?
A. Even though the sun won't turn into a black hole, if it did without gaining or losing any mass, the only effect on our Earth would be EXTREME freezing temperatures. The earth wouldn't get suck up because it has the same amount of mass and the same amount of gravitational attraction.
10. Q. How many types of black holes are there?
A. Three, a stationary black hole (Schwarzschild Black Hole), a rotating black hole (Kerr Black Hole), and an electrically charged black hole (Reissner-Nordström Black Hole). However in the real world only rotating black holes are likely to exist (nothing in the universe is truly stationary and any electrical charge on a black hole would tend to be neutralized rapidly).
11. Q. What is a Schwarzchild Radius?
A. It is the distance to the center (singulatity) of a stationary black hole to it's outer region (Event horizion).
12. Q. Do galaxies contain supermassive black holes in their centers?
A. Recent calculations predict that there are supermassive black holes in the center of most (if not all) galaxies, including the Milky Way.
