Rendereing of a Black HoleCredit: photo courtesy of NASA


 Black holes are the foundation of many plots in science fiction movies, novels and television shows.  For years, scientists have studied the possibility of the theory of the black hole and initially concluded there was no such thing in reality.  With the exploration of space, however, there is more evidence that black holes do occur and exist, though the closest one to earth is light years away.  There is a large volume of work about black holes and much of it is difficult to understand for the average person.  In layman’s terms--just what are these phenomena of space?

 What is a Black Hole

 The simple definition of a black hole is a compact mass which has a gravitational pull so strong nothing is able to escape.  To escape the object; the movement would have to be at a velocity faster than the speed of light.  There is nothing known to man faster than the speed of light; therefore, nothing can escape the object.  Typically, the objects are collapsed stars. 

 In the 18th century as scientists explored the theories of gravity and proposed the theory of the black hole, they concluded the smaller the size or the more massive an object, the more gravitational pull could be felt on its surface.  John Mitchell and French scientist Pierre-Simon Laplace contended if an object was either extremely small or extremely large, there was the possibility nothing, not even light, could escape its gravitational pull.  The term black hole was not coined until 1967 when John Archibald Wheeler introduced it to the science community.  Since then mathematicians and physicists have learned space and time near black holes have unusual properties.

 Black holes form when stars collapse from the compression of their own gravity.  Another type of the phenomena, the Stellar-mass, is born when stars at least 25 times heavier than our sun runs out of nuclear fuel and explodes as a supernova. A third type, Supermassive blackholes, are significantly heavier than stellar-mass black holes and exist in the center of a galaxy.  Not much is known about how these are formed.

 The Event Horizon

 The event horizon around a black hole is considered the point of no return.  This is the point at which any path light can take, and thus any forward path of light cone particles within the horizon, is warped such that it falls further into the hole.  Therefore, once a particle crosses into the horizon, it is inevitable it will fall into the black hole.   Passing Through the Event HorizonCredit: photo courtesy of NASA

 Once matter is pulled into the event horizon and sucked into the hole, it is squashed into the central singularity; a region of infinitely small volume.  The event horizon is like an imaginary sphere surrounding the central singularity. The size of the event horizon is proportional to the mass of the black hole.  The size of the sphere is called the Schwarzschild radius after the German physicist, Karl Schwarzschild, the man who discovered it based on his study of Einstein’s theory of relativity. 

 Do Black Holes Actually Exist

 The simple answer to the question of whether or not blackholes exits is yes, they do.  The universe is vast and there is no way of knowing how many black holes there actually are; however, there are none known close enough to earth to cause any danger. 

 Earth’s galaxy, the Milky Way, contains approximately 100 billion stars.  About one of every thousand stars has enough mass to become a black hole; therefore, it stands to reason there would be around 100 million stellar-mass holes.   The majority of them are invisible to human eyes and only about a dozen have actually been identified; the nearest of which is at least 1600 light-years from earth.  On top of that, there are billions of galaxies in the universe.  In addition, moBlack Hole in SpaceCredit: photo courtesy of NASAst of the galaxies contain supermassive black holes in the center, so exponentially there are millions of black holes in the universe.

 In January of 2001, the Hubble telescope measured chaotic fluctuations in ultraviolet light from gas trapped in the orbit of a black hole.  Flashes of light from the hot gas were caught spiraling into the hole.  From what was captured by the telescope, it appeared to match theories of what scientists predicted would be seen when light from matter falling close to the event horizon dims as gravity stretches it to longer wavelengths.

 The Growth and Death of Black Holes

 This space phenomenon grows by sucking in the gas, dust, and star debris that gets close to it.  Unlike the science fiction stories, black holes do not draw in matter from great distances away.  The bigger holTwo Blackholes MergingCredit: photo courtesy of NASAes can swallow whole planets when they come within the event horizon, and holes can grow when they merge and collide.

 Since nothing can escape a black hole, it was long believed they would live forever.  In 1974 the well-known physicist Stephen Hawking used the laws of quantum mechanics to study the area close to the event horizon.  These studies showed the black holes eventually evaporate.  To the layperson it appears as if the black hole is glowing as microscopic particles actually do escape as light is continually created and destroyed by the hole.  This Hawkings glow carries away energy and decreases the black hole’s mass until it is completely gone.  For the known holes existing in the universe today, the Hawking’s glow doesn’t matter.  It would take a long, long time for the energy to decrease their mass.  However, the discovery showed there is much to learn about black holes.


 Reference: accessed February 12, 2012 accessed February 12, 2012 accessed February 12, 2012

The American Heritage® Science Dictionary 2005 by Houghton Mifflin Company. Published by Houghton Mifflin Company


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