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Sample essay topic, essay writing: Black Holes - 1540 words

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.. Let's say that you weigh 110 lbs standing on the surface of normal Earth. As you get closer to the Earth-black hole you would feel a stronger and stronger force. If you got past 3189 km, (which is half the radius of normal Earth) of the Earth as a black hole you would weigh 440 lbs. That's very heavy! If you were to dig to 3189 km of the center of the earth you would weigh about 60Ibs, since the inside of the Earth's mass is smaller, it's more comparable to you.

Think about the Sun. If the Sun was to also become a black hole (which is impossible) the Earth would keep its normal orbit and would feel the same force of gravity from the Sun as usual, since the distance is still the same. In order to be 'sucked up' by a black hole, you have to get very close, if not you will experience the same force of gravity as if the black hole was still the normal star it used to be. As you get close to a black hole, the effects of relativity will become important. For example, the escape velocity gets bigger, which is defined as "the minimum velocity needed to escape a gravitational field" and in time it reaches the speed of light and then things like the 'event horizon" effect will start to happen

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Once you're past the event horizon you cannot turn back because the black hole's force is too strong for even the speed of light. Stars can only become black holes if they have large masses. For example, our Sun isn't massive enough to become a black hole. When the Sun runs out of the nuclear fuel in its core, four billion years from now it will die, but it will not become a black hole. Stars like this type die as white dwarf stars. Stars that are more massive stars, like those with masses that are over 20 times our Sun's mass, will probably create a black hole sooner or later. When a massive star runs out of nuclear fuel it won't be able to carry its own weight causing it to die. When this happens the star becomes hot and some fraction of its outer layer, which usually contains some nuclear fuel, will activate the nuclear reaction again and cause an explosion which is known as a supernova.

The rest of the inside of the star, the core, continues to fall down. The star may become a neutron star and stop falling, or if it keeps falling apart it may become a black hole. This all depends on the mass of the star. The dividing mass of the core, which determines what will happen to it, is about 2.5 solar masses. It is thought that to produce a core of 2.5 solar masses the ancestral star should begin with over 20 solar masses.

A stellar black holes is a black holes which was formed from a star.There might be three types of black holes, they are stellar, supermassive, and miniature black holes. It all depends on their size. These black holes have also formed in different ways. I already described how stellar black holes were formed. Supermassive black holes probably exist in the centers of most galaxies, including our own galaxy, the Milky Way.

They can have a mass that is euqual to billions of suns. In the outer parts of galaxies there are huge distances between stars. Although, in the area that is the center of galaxies, stars are packed very close together. Because everything in the central region is packed, a black hole in the center of a galaxy can get bigger and bigger as stars that are near it get sucked into the black hole. By measuring the velocity of stars that are orbiting close to the center of a galaxy, we can assume that there is a supermassive black hole and estimate the mass. In the supermassive black hole, there are sometimes two jets of hot gas.

These jets can be up to millions of light years in length. They are probably caused by the contact of gas particles with strong, turning magnetic fields that surround the black hole. Some observations made with the Hubble Space Telescope have given us the best evidence to date that supermassive black holes exist.It is not known how miniature black holes develop, but there are some ideas. First, is that they might have been formed right after the 'Big Bang,' which is thought to have started the Universe about 15 billion years ago. At that point the rapid expansion of some matter might have compressed slower matter creating black holes. Some scientists believe that black holes can evaporate and explode.

The time that is needed for evaporation would depend on the mass of the black hole. Massive black holes would need a longer time than the age of the universe. Miniature black holes are thought to be able to evaporate at the current age of our universe. For a black hole formed at the time of the 'Big Bang' to evaporate today its mass must be about 1015g (i.e., about 2 trillion pounds), a little more than twice the mass of the current Homo sapien population on planet Earth. During the final part of the 'evaporation,' a black hole would explode with a force several trillion times greater than the most powerful nuclear weapon.

So far, there is no proof that miniature black holes exist.With the use of Newton's Laws in the late 1790s, John Michell of England and Pierre LaPlace of France suggested an invisible star could exist. Michell and LaPlace estimated the mass and size,( which is now known as the event horizon) that an object needs for it to have an escape velocity that is bigger than the speed of light. In 1967 John Wheeler, an American theoretical physicist, described these collapsed objects as black holes, and the name just stuck like that.Astronomers have found evidence for supermassive black holes. They based this on measurement of gas around the black hole. In 1994, a measurement from the Hubble Space Telescope showed a huge mass at the center of a galaxy (M87).

The mass was about 3 billion times the mass of our Sun and appears to be concentrated into a space smaller than our solar system. For a lot of years x-rays from the double-star system Cygnus X-1 convinced many astronomers that the system had a black hole. With better measurements tools, the evidence for a black hole in Cygnus X-1 is very strong.A black hole is not seen since light can't escape it. In order for a black hole to be found the matter surrounding it has to be seen. Matter that surrounds a black hole heats up and gives off radiation so that it can be found.

Around a stellar black hole this matter is made up of gas and dust. Around a supermassive black hole in the center of a galaxy the swirling disk is made of gas and stars. In February of 1997 an instrument called the Space Telescope Imaging Spectrograph (STIS) was installed in the Hubble Space Telescope. STIS is the space telescope's black hole hunter. A spectrograph uses prisms to create rainbow patterns.

The STIS can take a spectrum of many places at the same time. Each spectrum tells scientists information about the gas around stars. With that information, the mass that the stars are orbiting can be estimated. The more massive the central object is, the faster the stars go. STIS found a supermassive black hole in the center of the galaxy M84. There was a rotation of 400 km/s, which is equal to 1.4 million km every hour.

The Earth orbits our Sun at 30 km/s. If Earth moved as fast as 400 km/s our year would be only 27 days long.The Advanced Camera for Surveys, which was installed in March 2002, represents the third generation of science instruments flown aboard the Hubble Space Telescope. It has a wider field of view, better image quality and better sensitivity. The new camera has double the field of view and has much more capabilities than the Hubble. The telescope with ACS's technology will make it ten times more useful and it will also last longer. ACS is probably going to work better than all the other instruments flown on the Hubble Space Telescope, because of ACS's increased wavelength range. Since the ACS was created to study some of the earlier activities in the universe, ACS will see from ultraviolet to infrared light.On the inside, the new instrument has three different cameras each doing different things.

The wide field camera, the high-resolution camera, and the solar blind camera. For example, with a greater field view than the Hubble's, ACS's wide camera can do surveys of the universe. Astronomers will use it to study the galaxies in more detail, which will show more clues about how our universe has grown. The camera will take excellent pictures of the inside regions of galaxies. It will search for other stars or planets and will take close-up images of the planets in our own solar system.

The solar blind camera, will focus on hot stars producing radiating in ultraviolet wavelengths.

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