- What is a Black Hole
A black hole is formed when a star of sufficient mass (at least 3 time the size of our sun) undergoes gravitational collapse, with most or all of its mass compressed into a sufficiently small area of space, causing infinite spacetime curvature at that point (a "singularity"). Such a massive spacetime curvature allows nothing, not even light, to escape from the "event horizon," or border.
Stars are powered by nuclear fuel; most stars use hydrogen. The larger a star is, the faster it will use up its fuel, and thus, the sooner it "dies". If the stars are large enough, however, then the gravitational pull will crush the star to 'zero volume', or in the Schwarzschild radius. This forms a black hole.
- There are currently 14 known black holes.
- Astronomers think that at least one black hole is born every day.
- The closest known black hole to Earth is Cygnus X-1, which is located about 8000 light years away.
- What would happen to our Solar System if the Sun were to suddenly become a black hole?
Not much! Other than getting very dark and very cold, nothing else would change. The planets would not be sucked into the black hole. Their orbits would not change since the mass of the Sun has not changed. Only the space the Sun occupies has changed. The gravity of a black hole is very powerful only when you are very close to it.
- Although black holes have a strong suction force, they may only suck up what crosses their event horizons, and, therefore, are not capable of absorbing the whole universe.
- How much would a feather weigh on the "surface" of a black hole?
Several billion tons! The weight of an object is determined by the mass of an object and how much gravity is affecting the mass. The force of gravity near a black hole is extremely strong. Under this extremely strong gravitational pull, the object would weigh several billion tons.
- What would happen to an astronaut if he tripped and fell into a black hole?
The astronaut would be stretched like a piece of spaghetti! The closer he got to the black hole, the stronger the force of gravity would be. In fact, the pull of gravity increases so fast, that the gravity tugs on his feet more than on his shoulders. With his feet being pulled into the black hole faster than his shoulders, he would be stretched out farther and farther, like a piece of spaghetti.
- Could you watch this stretched out astronaut enter the black hole?
No! Einstein's theories of relativity tell us that as you approach an object that has a great deal of mass (like a black hole) time slows down. The closer the astronaut gets to the black hole, the more time slows down. When the astronaut reaches the event horizon time stops. To the astronaut however, time is normal, so they will see themselves enter the black hole, assuming of course they could survive the gravity.
- Will black holes devour the universe?
Probably not. Black holes only severely affect the space within a few thousand miles of them. In the field of astronomy, a few thousand miles is considered a very small distance.
- Could someone survive a trip through a black hole?
No! You would be killed by many things before you could enter the black hole. Gravity would pull you apart. X-rays and other forms of radiation would be lethal. Even though your lifeless form would appear to be suspended over the black hole forever, the atoms that make up your body could never be rescued from the black hole.
- Black holes have no color, or light, or anything else we can use to identify them. This famous statement reminds us that once matter is inside a black hole, we can't tell what it was. As far as we could tell, or the black hole could tell, the matter inside could be made of elephants, cockroaches, toasters or anything else! The only things we can use to identify a black hole is its mass, electrical charge, and the amount of rotation it has.
- Why are black holes black?
In order for a rocket to leave the surface of Earth, it must travel faster than 25,000 miles per hour (7 miles per second). This is called escape velocity. If the rocket has a speed less than the escape velocity of an object, the object's gravity will pull it back down. The escape velocity of a black hole is greater then 186,000 miles per second. That means a rocket would have to travel faster than 186,000 miles per second in order to leave the black hole. The speed of light is 186,000 miles per second, so light doesn't travel fast enough to leave the black hole, hence it is black.
- The center of a black hole, the singularity, is the point where the laws of physics break down. These singularities are hidden by the black hole, so that the effects of the breakdown cannot be observed by people outside.
- Although whiteholes are mathematically possible, there have yet to be observations to prove their existence.
- According to Einstein's theories of relativity, nothing can travel faster than the speed of light. Therefore once an something is inside a black hole it can never get out.
- If you get close enough to a black hole you will see the back of your own head! This effect is called an Einstein ring, this is caused by the intense gravity around a black hole. When you are near a black hole at certain distances the light that leaves from the back of your head will travel though space that is bent so much by gravity that it will enter your eyes.
Black Holes Glossary of Terms
• Accretion disk: A disk of matter that forms when a large amount of material falls into a
black hole. The disk is outside the event horizon of the black hole. Friction and other forces
heat the disk, which then emits light.
• Escape velocity: The velocity needed for an object to become essentially free of
gravitational effect of another object.
• Event horizon: The distance from the center of a black hole where the escape velocity is
equal to the speed of light.
• Galaxy: A collection of gas, dust and billions of stars held together by their mutual gravity
• Gamma-ray burst: An enormously energetic explosion of high-energy light, some of which
is thought to be due to the formation of a black hole.
• Gravity: The attractive force of an object that depends on its mass, and your distance from
it. The more massive an object, or the closer you are to it, the stronger the force of its
gravity will be.
• Mass: The quantity of matter that makes up an object.
• Supernova: An exploded, or exploding, star.
• Wormhole: A theoretical shortcut through space caused when a black hole punches
through the fabric of space&time. While possible mathematically, in reality they probably do