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Are Black Holes Fuzzballs?
A string theory description of the insides of black holes is surprising scientists.
NASA artist concept of how a black hole might look if it were surrounded by a disk of hot gas and a large doughnut, or torus, of cooler gas and dust. The light blue ring on the back of the torus comes from the fluorescence of iron atoms excited by X-rays from the hot gas disk.
[click to enlarge NASA/CXC/SAO photo]
Most cosmologists used to believe that anything that entered a black hole ceased to exist. That is, the interior of a black hole was not changed by particles that entered it.
Now, physicists at Ohio State University understand that all particles in the Universe are made of tiny vibrating strings.
Their equations suggest things that enter a black hole continue to exist and, in fact, become bound up in a giant tangle of strings that fills a black hole from its core to its surface.
In other words, black holes are not smooth and featureless as had been thought. Instead, they are stringy fuzzballs.
How black holes are born. Astronomers believe a black hole forms when a supermassive object – a dying giant star – collapses in on itself to form a very small point of infinite gravity.
That point is called a singularity.
A special region in space surrounds the singularity. The border of that region is known as the event horizon.
Any object that crosses the event horizon is pulled into the black hole, never to return. That means that not even light can escape from a black hole.
How big is a black hole? The diameter of the event horizon depends on the mass of the object that formed it. For instance:
- If the Sun were to collapse into a singularity, its event horizon would be about 1.9 miles across.
- If the collapsing body were Earth, its event horizon would be only 0.4 inches across.
So far, physicists have not known what lies between the event horizon and the singularity. That is, that don't know what is inside the black hole.
What is a Singularity?
The center of a black hole is a singularity.
NASA's Goddard Space Flight Center defines it as, "A place where spacetime becomes so strongly curved that the laws of Einstein's general relativity break down and quantum gravity must take over."
It also has been defined as:
- the point where the curvature of space-time is infinite.
- the point at which spacetime becomes compressed to the point of being infinitely dense and infinitely small.
- the zero-dimensional point at the center of a black hole or other significant object – such as the Universe at the instant of the Big Bang – at which all conceptions of space and time break down and become incomprehensible.
- the dimensionless point at the center of a black hole, where all the mass of the collapsing star has shrunk to infinite density.
- the object of zero radius into which the matter in a black hole is believed to fall.
Previously, they had thought there was no structure or anything measurable inside the event horizon. The inside of a black hole was uniform and featureless throughout.
What was wrong with the old theory? The problem with the old theory was physicists must be able to trace the end product of any process, including the process that makes a black hole, back to the conditions that created it. But, if all black holes are the same, then no black hole can be traced back to its unique beginning, and any information about the particles that created it is lost forever at the moment the hole forms.
Now the Ohio State researchers have described the structure of black holes in a new way. According to string theory, all the fundamental particles of the Universe – protons, neutrons, electrons – are made of different combinations of strings. But as tiny as strings are, they can form large black holes through a phenomenon known as fractional tension.
Strings can be stretched, but each carries a certain amount of tension, like a guitar string. With fractional tension, the tension decreases as the string gets longer. Just as a long guitar string is easier to pluck than a short guitar string, a long strand of quantum mechanics strings joined together is easier to stretch than a single string, according to the new theory.
So, when a great many strings join together, as they would in order to form the many particles necessary for a very massive object like a black hole, the combined ball of string is very stretchy, and expands to a wide diameter.
When the Ohio State physicists derived their formula for the diameter of a fuzzy black hole made of strings, they found that it matched the diameter of the black hole event horizon suggested by the old theory.
Since the new theory suggests strings continue to exist inside a black hole, and the nature of the strings depends on the particles that made up the original source material, then each black hole is as unique as are the stars, planets, or galaxy that formed it.
The strings from any subsequent material that enters the black hole would remain traceable. That means a black hole can be traced back to its original conditions, and information about what entered survives.
SOURCE: OHIO STATE UNIVERSITY
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