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How black holes work

You may have heard someone say, “My desk has become a black hole!” You may have seen an astronomy program on television or read a magazine article on black holes. These exotic objects have captured our imagination ever since they were predicted by Einstein’s Theory of General Relativity in 1915

What is a black hole: A black hole is what remains when a massive star dies.

History: The concept of an object from which light could not escape (e.g., black hole) was originally proposed by Pierre Simon Laplace in 1795. Using Newton’s Theory of Gravity, Laplace calculated that if an object were compressed into a small enough radius, then the escape velocity of that object would be faster than the speed of light. A star is a huge, amazing fusion reactor. Because stars are so massive and made out of gas, there is an intense gravitational field that is always trying to collapse the star. The fusion reactions happening in the core are like a giant fusion bomb that is trying to explode the star. The balance between the gravitational forces and the explosive forces is what defines the size of the star.

As the star dies, the nuclear fusion reactions stop because the fuel for these reactions gets burned up. At the same time, the star’s gravity pulls material inward and compresses the core. As the core compresses, it heats up and eventually creates a supernova explosion in which the material and radiation blasts out into space. What remains is the highly compressed, and extremely massive, core. The core’s gravity is so strong that even light cannot escape.

This object is now a black hole and literally disappears from view. Because the core’s gravity is so strong, the core sinks through the fabric of space-time, creating a hole in space-time — this is why the object is called a black hole.

The core becomes the central part of the black hole called the singularity. The opening of the hole is called the event horizon.

Types of black holes: There are two types of black holes: Schwarzschild - Non-rotating black hole

Kerr - Rotating black hole

The Schwarzschild black hole is the simplest black hole, in which the core does not rotate. This type of black hole only has a singularity and an event horizon. The Kerr black hole, which is probably the most common form in nature, rotates because the star from which it was formed was rotating. When the rotating star collapses, the core continues to rotate, and this carried over to the black hole.

How we detect black holes: Although we cannot see black holes, we can detect or guess the presence of one by measuring its effects on objects around it. The following effects may be used: Mass: Many black holes have objects around them, and by looking at the behaviour of the objects you can detect the presence of a black hole. You then use measurements of the movement of objects around a suspected black hole to calculate the black hole’s mass.

What you look for is a star or a disk of gas that is behaving as though there were a large mass nearby. You then estimate the mass of the black hole by looking at the effect it has on the visible object.

Gravity lens: Einstein’s General Theory of Relativity predicted that gravity could bend space. Therefore, an object with immense gravity, like a black hole, between the Earth and a distant object could bend the light from the distant object into a focus, much like a lens can. Emitted radiation: When material falls into a black hole from a companion star, it gets heated to millions of degrees Kelvin and accelerated. The superheated materials emit X-rays, which can be detected by X-ray telescopes.

It is important to remember that black holes are not cosmic vacuum cleaners — they will not consume everything. So although we cannot see black holes, there is indirect evidence that they exist. —Howstuffworks.com

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