A black hole is one of the most intriguing objects in the universe and the science of Astronomy. It is all that remains after a massive star has completed burning its nuclear fuel. Stars exhibit a delicate balance between the energy produced by fusion of its fuel and the huge amount of gravity possessed by its mass. When a star has exhausted its nuclear fuel, it no longer has the energy to counteract the tremendous force of its own gravity. The star then implodes under its own immense gravity and compresses or shrinks to a single point, called a singularity (a.k.a. black hole). At this point, pressure and density become infinite. The current knowledge suggests that any object that gets too close to a black hole is pulled in, stretched to infinity, and trapped forever. The gravity exhibited by a black hole is calculated to be so large that nothing can escape, not even light. However, high amounts of energy have been measured streaming from some black holes suggesting that physical-chemical reactions occur to the materials as they are being pulled in and heated. As materials are heated, they emit tremendous amounts of x-rays and gamma rays.
Black Hole Anatomy
Not all stars will end up to become black holes. Special circumstances are required to create such massive singularities of gravity. A black hole forms when its pre-cursor star has sufficient mass to create a massive implosion. Giant stars more than three times the mass of our Sun are thought to be large enough to implode to form a black hole. Without sufficient mass, dying stars can have other ends, such as white dwarfs, brown dwarfs, or red giants.
Average-sized stars, like our Sun, shrink to become white dwarfs (small, extremely dense stars having low brightness) about the size of Earth. (Although, there are other theories that suggest our Sun may also become a red giant in its dying days). However, stars that are three times the mass of the Sun and greater, may have the required mass and gravity to form a huge gravity singularity.
Black holes cannot be seen, so how do we they know they exist? Astronomers have not witnessed a black hole directly, however there are several ways they know of their existence. One method is to observe nearby stars that are not close enough to be pulled in, but are close enough to be affected by the black hole’s tremendous gravitational pull. Observations of the orbits for several stars over time can be tracked by a telescope and computers are then able to calculate the relative position of the central area around which all the stars are orbiting.
In addition, physicists have been able to calculate their existence. There is no way I can possibly explain the complex calculations they use to determine their existence, however, rest assured we can rely on physicists to be correct.
We can use escape velocity to illustrate what it would take to escape large objects in space and then extend this to black holes. For example to escape Earth’s gravity, we would have to travel at a speed of a minimum of 7 miles per second. To escape the Sun, we would have to travel at 380 miles per second. We could extend this idea to an object so massive and so dense that the escape velocity of light is exceeded (186,000 miles per second). Objects with such massive gravity have been determined to exist, therefore nothing would be able to escape their gravity not even light.
Black Holes Can Warp Space and Time
According to the famous Albert Einstein’s (1879–1955) general theory of relativity, space becomes curved near massive objects that are extremely dense. The greater the density, the more space is curved. When a black hole forms, space curves so much, that only a small opening to the rest of normal space remains. The surface of this opening is called the event horizon, a theorized point of no-return. Any matter that crosses the event horizon is drawn in by the black hole’s gravity and cannot escape, vanishing across the event horizon forever. What happens inside a black hole is unknown.
Einstein considered space and time were both relative, indicating they BOTH could change. Evidence of Einstein’s theory of time warping was determined by examination of extremely accurate clocks in satellites in orbit above the earth over 200 miles up. Clocks in these satellites were shown to run faster than those on Earth by a very small amount (1 ten thousandth of a third of a second). This time difference was verified carefully numerous times. It was clear, that objects on such a massive object such as the earth, exhibited slower time than objects only 200 miles away. Extrapolate this theory to the super massive black holes that have been calculated to exist, and you would find that time stands still at a black hole!
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