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Wednesday, September 14, 2011

Essay on Black Holes

Black holes are simply the last stage in the existence of stars which are at least 10 to 15 times as big as the Sun.  When stars which are as big as the Sun reaches its death, it undergoes a supernova explosion. When this happens, the star leaves behind residues and remnants.  Since it does not have a size that can oppose or repel gravitational force, the usual tendency is that the remnant of the star collapse in on itself.  Eventually, the star reaches the stage of zero volume creating what is known as singularity.   As the density continues to increase, the light rays emitted from the star will be bent and wrapped around it.  Moreover photons which are emitted will be trapped into an orbit by its strong gravitational field.  At this point, no light will be able to escape.  It is now called the black hole. 

Because of its strong gravitational field, black holes are considered the bullies in the cosmic world. They acquired such bad reputation in view of the nature of their gravitational field that is so strong and powerful that nothing can escape it.  Astronomers have already confirmed the fact that not even light can escape the gravitational pull of a black hole.  Matthew Bershady, a professor of astronomy at University of Wisconsin-Madison explained that a person can jump higher on the moon because the moon has less mass which makes its gravity weaker.  On the other hand, if a celestial body is more massive, it gets more difficult to jump and escape its gravity.  Just imagine when a gravity of a celestial body is so strong then it would not be really possible for anything to escape its pull.  Thus, it acquired the name black hole because it is literally black and it absorbs all the light that comes within its path and that everything gets sucked into its hole.  

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It must however be stressed that contrary to myths and urban legends, black holes are not vacuum cleaners of the cosmic world.  This means that black holes do not simply suck everything within its path.  If the Sun will be replaced by a black hole, the Earth will remain on its orbit and its path will remain unchanged.  Thus, it does not follow that every planet that revolves around the sun will be sucked into the black hole, in case the sun is replaced by a Black hole.  To be sucked into a black hole, scientists say that one has to cross inside the Schwarzschild radium.  According to Goddard Space Flight Center, the Schwarzschild radius can be calculated using the following equation: 
vesc = (2GM/R)1/2

Based on this equation, if the sun was replaced by a black hole which is as massive, the Schwarzschild radium would be 3km.  This means that the Earth would have to be as close as 3km before it can get sucked into a black hole. 

Astronomers say that there is still so much to be known about black holes.  For instance, it was only in November 2002 that astronomers learned that super massive black holes actually exist.  It was reported in November 19, 2002 that Chandra X-ray telescope collected images from a galaxy known as NGC 6240 showing that it produces X-radiation.  Astronomers have long believed that the emission of X-radiation is a sign that there are super massive objects in this galaxy.  Further investigation revealed that NGC 6240 actually harbors two giant black holes both of which are active and are sucking in materials from their surroundings with their powerful gravitational pull.  Ray Villard, a professor of astronomy at Johns Hopkins University in Baltimore, said that this reinforces the theory that most if not all galaxies harbor super massive black holes.  It also suggests that when to galaxies merge, which is what happened with NGC 6240, the black holes existing therein may be drawn closer together. 

In addition, astronomers stress the magnitude of the impact in case black holes collide.  They say that there will be an enormous burst of gravitational radiation when smaller black holes merge into one massive black hole.  It may even be possible that the impact of the collision may knock out the black hole out of its galaxy.

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