Black Holes
Ever wonder what it would be like to journey near a black hole?? what does the approach to a point of infinite density and infinite gravity feel like?
Here is a cool website with loads of great facts...
Black Holes: gravity's relentless pull.
What are black holes?
A black hole is a region of space in which the gravitational field is so powerful that nothing can escape after having fallen past the event horizon. The name comes from the fact that even light is unable to escape, rendering the interior invisible. However, black holes can be detected if they interact with matter outside the event horizon.
What are the sizes of black holes?
Supermassive, Intermediate-mass, and Stellar-mass black holes are enormous, as for the Micro black holes for they are small. Believed to exist in the center of most galaxies, the supermassive black holes has billions of times the mass of the sun. Whose size is measured in thousands of solar masses, the Intermediate-mass black holes have been proposed as a possible power source for ultra-luminous X-ray sources. Who have masses ranging from about 1.5-3.0 solar masses (the Tolman-Oppenheimer-Volkoff limit) to 15 solar masses. The Stellar-mass black holes are created by the collapse of individual stars. which have masses at which the effects of quantum mechanics the micro black holes are expected to become very important. The term micro black hole or mini black hole may refer to any black hole with mass less than a star.
Why is it impossible to escape from black holes?
There are several ways of describing the situation that causes escape to be impossible. The difference between these descriptions is how space and time coordinates are drawn on spacetime(the choice of coordinates depends on the choice of observation point and on additional definitions used). One common description, based on the Schwarzchild description of black holes, is to consider the time axis in spacetime to point inwards towards the center of the black hole once the horizon is crossed. Under these conditions, falling further into the hole is as inevitable as moving forward in time. A related description is to consider the future light cone of a test object near the hole (all possible paths the object or anything emitted by it could take, limited by the speed of light). As the object approaches the event horizon at the boundary of the black hole, the future light cone tilts inwards towards the horizon. When the test object passes the horizon, the cone tilts completely inward, and all possible paths lead into the hole.
What happens when I or a clock fall into a black hole?
Earth does not fall into the Sun because we move around it at a speed of some 67 thousand miles per hour. But the orbits near a black hole can have various interesting shapes, whereas those in the solar system are always elliptical (and almost circular).Suppose that you are near a black hole and launch a spaceship to study it up close. If you start too slow, you will spiral into the black hole. If you start too fast, you will fly into the far off distance. At intermediate speeds you will orbit the black hole in a complicated pattern. There is exactly one launch speed that will put you on a circular orbit. This provides a stable vantage point if you start far from the black hole, but it is like playing Russian roulette if you start too close. In that case, even the smallest movement on your ship will drastically change your orbit. You might drift away from the black hole, but if you are unlucky you will spiral into it.
If you actually read the whole thing you should know alot about black holes now and it won't hurt to read it so read it.
Why is it impossible to escape from black holes?
There are several ways of describing the situation that causes escape to be impossible. The difference between these descriptions is how space and time coordinates are drawn on spacetime(the choice of coordinates depends on the choice of observation point and on additional definitions used). One common description, based on the Schwarzchild description of black holes, is to consider the time axis in spacetime to point inwards towards the center of the black hole once the horizon is crossed. Under these conditions, falling further into the hole is as inevitable as moving forward in time. A related description is to consider the future light cone of a test object near the hole (all possible paths the object or anything emitted by it could take, limited by the speed of light). As the object approaches the event horizon at the boundary of the black hole, the future light cone tilts inwards towards the horizon. When the test object passes the horizon, the cone tilts completely inward, and all possible paths lead into the hole.
What happens when I or a clock fall into a black hole?
Let's assume that you start outside the event horizon of the black hole. As you look toward it, you see a circle of perfect darkness. Around the black hole, you see the familiar stars of the night sky. But their pattern is strangely distorted, as the light from distant stars gets bent by the black hole's gravity.
As you fall toward the black hole, you move faster and faster, accelerated by its gravity. Your feet feel a stronger gravitational pull than your head, because they are closer to the black hole. As a result, your body is stretched apart. For small black holes, this stretching is so strong that your body is completely torn apart before you reach the event horizon.
If you fall into a Supermassive black hole, your body remains intact, even as you cross the event horizon. But soon thereafter you reach the central singularity, where you are squashed into a single point of infinite density. You have become one with the black hole. Unfortunately, you are unable to write home about the experience.
Imagine that we are on a spaceship near a black hole. We drop a clock into the black hole and compare its time to that of our onboard clock. The falling clock runs progressively slower. It never crosses the event horizon, but stays frozen there in space and time. The falling clock also becomes continuously redder, since its light loses energy as it escapes from the black hole's vicinity.
By contrast, if we were falling with the clock, time would appear to behave perfectly normally. We would see no slowdown as we approached the event horizon. We would cross the horizon without any perceptible change, and our color would not appear to change. This is the principle of relativity: things can appear different depending on whether you are moving or standing still.
Can we orbit a black hole?
As you fall toward the black hole, you move faster and faster, accelerated by its gravity. Your feet feel a stronger gravitational pull than your head, because they are closer to the black hole. As a result, your body is stretched apart. For small black holes, this stretching is so strong that your body is completely torn apart before you reach the event horizon.
If you fall into a Supermassive black hole, your body remains intact, even as you cross the event horizon. But soon thereafter you reach the central singularity, where you are squashed into a single point of infinite density. You have become one with the black hole. Unfortunately, you are unable to write home about the experience.
According to Einstein's theory of general relativity, massive objects create distortions in space and time. Near a black hole, these distortions become so strong that time behaves in unexpected ways.
Imagine that we are on a spaceship near a black hole. We drop a clock into the black hole and compare its time to that of our onboard clock. The falling clock runs progressively slower. It never crosses the event horizon, but stays frozen there in space and time. The falling clock also becomes continuously redder, since its light loses energy as it escapes from the black hole's vicinity.
By contrast, if we were falling with the clock, time would appear to behave perfectly normally. We would see no slowdown as we approached the event horizon. We would cross the horizon without any perceptible change, and our color would not appear to change. This is the principle of relativity: things can appear different depending on whether you are moving or standing still.
Can we orbit a black hole?
Earth does not fall into the Sun because we move around it at a speed of some 67 thousand miles per hour. But the orbits near a black hole can have various interesting shapes, whereas those in the solar system are always elliptical (and almost circular).Suppose that you are near a black hole and launch a spaceship to study it up close. If you start too slow, you will spiral into the black hole. If you start too fast, you will fly into the far off distance. At intermediate speeds you will orbit the black hole in a complicated pattern. There is exactly one launch speed that will put you on a circular orbit. This provides a stable vantage point if you start far from the black hole, but it is like playing Russian roulette if you start too close. In that case, even the smallest movement on your ship will drastically change your orbit. You might drift away from the black hole, but if you are unlucky you will spiral into it.
If you actually read the whole thing you should know alot about black holes now and it won't hurt to read it so read it.
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