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Black Hole

Black holes are the densest, most massive singular objects in the universe.

Tina S
Tina S
Jan 21, 2010
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Science


 

In the 1700s, there were some who proposed that a super massive object might draw light into it. Newtonian optics was a corpuscular theory of light, treating light as particles.

The idea of a body so massive that even light could not escape was put forward by geologist John Michell in a letter written to Henry Cavendish in 1783 to the Royal Society:
 
If the semi-diameter of a sphere of the same density as the Sun were to exceed that of the Sun in the proportion of 500 to 1, a body falling from an infinite height towards it would have acquired at its surface greater velocity than that of light, and consequently supposing light to be attracted by the same force in proportion to its vis inertiae, with other bodies, all light emitted from such a body would be made to return towards it by its own proper gravity.
—John Michell
 
John Michell published a paper in 1784 predicting that an object with a radius 500 times that of the sun (but the same density) would have an escape velocity of the speed of light at its surface, and thus be invisible. Interest in the theory died in the 1900s, however, as the wave theory of light took prominence.
 
When rarely referenced in modern physics, these theoretical entities are referred to as "dark stars" to distinguish them from true black holes.
 
General Relativity:

According to the general theory of relativity, a black hole is a region of space from which nothing, including light, can escape. It is the result of the deformation of space time caused by a very compact mass. Around a black hole there is an undetectable surface which marks the point of no return, called an event horizon. It is called "black" because it absorbs all the light that comes towards it, reflecting nothing, just like a perfect black body in thermodynamics. Under the theory of quantum mechanics black holes possess a temperature and emit Hawking radiation.

A black hole is a theoretical entity predicted by the equations of general relativity. A black hole is formed when a star of sufficient mass undergoes gravitational collapse, with most or all of its mass compressed into a sufficiently small area of space, causing infinite space-time curvature at that point (a "singularity"). Such a massive space time curvature allows nothing, not even light, to escape from the "event horizon", or border. 

Black holes have never been directly observed, though predictions of their effects have matched observations. There exist a handful of alternate theories, such as Magnetospheric Eternally Collapsing Objects (MECOs), to explain these observations, most of which avoid the space-time singularity at the center of the black hole, but the vast majority of physicists believe that the black hole explanation is the most likely physical representation of what is taking place.

Black holes are the evolutionary endpoints of stars at least 10 to 15 times as massive as the Sun. If a star that massive or larger undergoes a supernova explosion, it may leave behind a fairly massive burned out stellar remnant. With no outward forces to oppose gravitational forces, the remnant will collapse in on itself.
 
The star eventually collapses to the point of zero volume and infinite density, creating what is known as a "singularity". Around the singularity is a region where the force of gravity is so strong that not even light can escape. Thus, no information can reach us from this region. It is therefore called a black hole, and its surface is called the "event horizon".

Contrary to Popular Myth:

But contrary to popular myth, a black hole is not a cosmic vacuum cleaner. If our Sun was suddenly replaced with a black hole of the same mass, the Earth's orbit around the Sun would be unchanged. (Of course the Earth's temperature would change, and there would be no solar wind or solar magnetic storms affecting us.) To be "sucked" into a black hole, one has to cross inside the Schwarzschild radius. At this radius, the escape speed is equal to the speed of light, and once light passes through, even it cannot escape.

The Schwarzschild radius can be calculated using the equation for escape speed:
 
vesc = (2GM/R)1/2
 
For photons, or objects with no mass, we can substitute c (the speed of light) for Vesc and find the Schwarzschild radius, R, to be
 
R = 2GM/c2

If the Sun was replaced with a black hole that had the same mass as the Sun, the Schwarzschild radius would be 3 km (compared to the Sun's radius of nearly 700,000 km). Hence the Earth would have to get very close to get sucked into a black hole at the center of our Solar System.

At the very center of the black hole is where our understanding breaks down. Einstein's theory of gravity seems to predict that time it is destroyed at the center of the hole: time comes to an abrupt end there. For this reason, a black hole is sometimes described as the "reverse of creation." But no one knows how or why time could come to an abrupt end, any more than we know how time was created in the first place. Einstein's theory of gravity no longer applies at these tiniest scales of distance and new laws of nature must be found that describe what happens at the center of a black hole.

Does the inside of a black hole lead to another universe?
 
The truth is, no one really knows. We cannot do a direct experiment to find out, even in principle, since no information or evidence can ever get back out of a black hole.
That's what makes it so important to find and study black holes from theoutside, while at the same time developing theories that can more confidently predict what might happen on the inside of the black hole.
 
Falling into black hole:

In which we fall into a black hole on a real free fall orbit. All distortions of images are real, both general relativistic from the gravitational bending of light, and special relativistic from the near light speed orbit.
 
The black hole belongs to a quadruple stellar system, a binary. The system is fictional, but plausible.
After you are done dying at the central singularity of the black hole, feel free to explore more about the Schwarzschild geometry, about wormholes, about the collapse of a black hole, and about Hawking radiation.
 
However, from your vantage point, as you enter the black hole, nothing has changed. As you look "out" of the hole, the universe still looks relatively normal.
 
However, you are drawn towards the singularity, and cannot escape its grasp. At this point, modern physics does not know what would happen. The most likely outcome is that you are compacted into a miniscule size upon the singularity.
 
However, you would not actually survive the fall into the hole. The immense warping of space around the hole would cause a spaghettification effect - you would be pulled apart because your feet (assuming they went feet first) would be far greater than the force on your head, and they you would be pulled as one pulls dough into a rope. This would be rather unpleasant, as well as fatal.

White Holes

The idea of a white hole is the opposite of a black hole, and is entertained more in science fiction than in actual science journals. Some believe it is the "other side" of a black hole. It is theorized to spew matter and energy out.
 
A flaw in this theory, as many scientists have noted, is that the matter ejected from the white hole would accumulate in the vicinity of the hole, and then collapse upon itself, forming a black hole.

 

 

Author's note: Oh..Very difficult to me to understand..:(
Keywords: black hole,quantum mechanic,myth,universe,falling,orbit,Henry Cavendish,John Michell,modern physics,theoretical,dark stars,Magnetospheric, Eternally, Collapsing,singularity,speed,light,white holes.



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