The+Physics+of+a+Black+Hole

Black Holes: What Are They?
====Black holes are the evolutionary endpoints of stars at least 10 to 15 times as massive as the Sun. If a star that is 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] ".==== ====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.====

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==== ========

[[image:http://archive.ncsa.illinois.edu/Cyberia/NumRel/Images/anatomy.gif]]
====By definition a black hole is a region where matter collapses to infinite density, and where, as a result, the curvature of spacetime is extreme. Moreover, the intense gravitational field of the black hole prevents any light or other electromagnetic radiation from escaping. But where lies the "point of no return" at which any matter or energy is doomed to disappear from the visible universe?====

====Applying the Einstein Field Equations to collapsing stars, German astrophysicist [|Kurt Schwarzschild] deduced the critical radius for a given mass at which matter would collapse into an infinitely dense state known as a singularity. For a black hole whose mass equals 10 suns, this radius is about 30 kilometers or 19 miles, which translates into a critical circumference of 189 kilometers or 118 miles.====

[[image:http://archive.ncsa.illinois.edu/Cyberia/NumRel/Images/basicsm.gif align="left"]]
====If you envision the simplest three-dimensional geometry for a black hole, that is a sphere (known as a Schwarzschild black hole), the black hole's surface is known as the **event horizon**. Behind this horizon, the inward pull of gravity is overwhelming and no information about the black hole's interior can escape to the outer universe.====

Apparent versus Event Horizon
====As a doomed star reaches its critical circumference, an "apparent" event horizon forms suddenly. Why "apparent?" Because it separates light rays that are trapped inside a black hole from those that can move away from it. However, some light rays that are moving away at a given instant of time may find themselves trapped later if more matter or energy falls into the black hole, increasing its gravitational pull. The event horizon is traced out by "critical" light rays that will never escape or fall in.====

[|Caption]
====Even before the star meets its final doom, the event horizon forms at the center, balloons out and breaks through the star's surface at the very moment it shrinks through the critical circumference. At this point in time, the apparent and event horizons merge as one: the horizon. For more details, see the caption for the above diagram.==== ====The distinction between apparent horizon and event horizon may seem subtle, even obscure. Nevertheless the difference becomes important in [|computer simulations] of how black holes form and evolve.==== ====Beyond the event horizon, nothing, not even light, can escape. So the event horizon acts as a kind of "surface" or "skin" beyond which we can venture but cannot see. Imagine what happens as you approach the horizon, then cross the threshold.====

====At the center of a black hole lies the singularity, where matter is crushed to infinite density, the pull of gravity is infinitely strong, and spacetime has infinite curvature. Here it's no longer meaningful to speak of space and time, much less spacetime. Jumbled up at the singularity, space and time cease to exist as we know them.====

Newton and Einstein may have looked at the universe very differently, but they would have agreed on one thing: all physical laws are inherently bound up with a coherent fabric of space and time.
====At the singularity, though, the laws of physics, including General Relativity, break down. Enter the strange world of **quantum gravity**. In this bizzare realm in which space and time are broken apart, cause and effect cannot be unraveled. Even today, there is no satisfactory theory for what happens at and beyond the singularity.====

Cosmic Censorship
====It's no surprise that throughout his life Einstein rejected the possibility of singularities. So disturbing were the implications that, by the late 1960s, physicists conjectured that the universe forbade "naked singularities." After all, if a singularity were "naked," it could alter the whole universe unpredictably. All singularities within the universe must therefore be "clothed."====

Science versus Speculation
====We can't see beyond the event horizon. At the singularity, randomness reigns supreme. What, then, can we really "know" about black holes? How can we probe their secrets? The answer in part lies in understanding their evolution right after they form.====


 * What types of black holes are there? **

Black holes often look very different from each other. But this is because of variety in what happens in their surroundings. The black holes themselves are all identical, except for three characteristic properties: the mass of the black hole (how much stuff it is made of), its spin (whether and how fast it rotates around an axis), and its electric charge. Amazingly, black holes completely erase all of the other complex properties of the objects that they swallow.

Astronomers can measure the mass of black holes by studying the material that orbits around them. So far, we have found two types of black holes: stellar-mass (just a few times heavier than our Sun) or supermassive (about as heavy as a small galaxy). But black holes might exist in other mass ranges as well. For example, recent observations suggest there may be black holes with masses between stellar-mass and supermassive black holes.

Black holes can spin around an axis, although the rotation speed cannot exceed some limit. Astronomers think that many black hole in the Universe probably do spin, because the objects from which black holes form (stars for example) generally rotate as well. Observations are starting to shed some light on this issue, but no consensus has so far emerged. Black holes could also be electrically charged. However, they would then rapidly neutralize that charge by attracting and swallowing material of opposite polarity. So astronomers believe that all black holes in the Universe are uncharged.

//**MythBusters**// is a science entertainment TV program created and produced by an Australian company, [|Beyond Television Productions][|[1]] originally for the [|Discovery Channel] in the United States. The series is screened by numerous international broadcasters, including [|SBS One] and the Discovery Channel in Australia, [|Discovery Channel Canada], [|Quest] and the Discovery Channel in the UK. The show's hosts, [|special effects] experts [|Adam Savage] and [|Jamie Hyneman], use elements of the [|scientific method] to [|test the validity] of rumors, myths, movie scenes, [|adages], Internet videos and news stories. Filming is based in [|San Francisco, California], though some elements of production are done in [|Artarmon, Australia]. Planning and some experimentation takes place at Hyneman's workshops; experiments requiring more space or special accommodations are filmed on location, typically around the [|San Francisco Bay Area] and other [|Northern California] places. During the second season, members of Savage and Hyneman's team ("The Build Team") were organized into a second team and now test myths separately from the main duo.

The series concept was created for the Discovery Channel as //**Tall Tales or True**//[|[2]] by Australian writer and producer [|Peter Rees] of Beyond Productions in 2002. Discovery rejected the proposal initially because they had just commissioned a series on the same topic. Rees refined the pitch to focus on testing key elements of the stories rather than just retelling them. Discovery agreed to develop and co-produce a three-episode series [|pilot]. Hyneman was one of a number of special effects artists who was asked to prepare a casting video for network consideration. Rees had interviewed him previously for a segment of the popular science series //[|Beyond 2000]// about the British/American [|robot combat] television series //[|Robot Wars]//. Savage, who had worked with Hyneman in commercials and on the [|robot combat] television series //[|BattleBots]//, was asked by Hyneman to help co-host the show because, according to Savage, Hyneman thought himself too uninteresting to host the series on his own.[|[3]][|[4]] During July 2006, an edited thirty-minute version of //MythBusters// began airing on [|BBC Two] in the UK. The episodes shown on the European Discovery Channel sometimes include extra scenes not shown in the U.S. version (some of these scenes are included eventually in "specials", such as //[|MythBusters Outtakes]//).

 Conclusions of the experiments By the end of each episode, each myth is rated "busted," "plausible," or "confirmed". Myths are confirmed as "Busted" when the myth's results cannot be replicated via either the described parameters, nor reasonably exaggerated ones. Often, when a myth is declared Busted, the team will attempt to see what would be required to replicate the result of the myth through scientific means, discarding the original parameters of the myth itself. This is commonly referred to in the series as "the MythBusters way", and often reveals that the circumstances required to accurately recreate a 'Busted' myth are physically impossible or highly unlikely to occur with the scientific facts presented, or the equipment used in the myth used to gain the results is neither available to civilians, or capable of producing the results.Some of these myths are retested if the viewers are dissatisfied with the results, and are declared "Re-Busted" if the results of this second attempt results in the same conclusion as the original attempt. On rare occasions, re-tested myths result in a different conclusion than the first attempt, usually going from "Busted" the first time, to "Plausible" or even "Confirmed" on the re-test. Plausible is given under a few circumstances: The MythBusters are able to recreate or closely recreate the myth's purported outcome with the described circumstances. A Confirmed myth is usually corroborated with documented evidence of actual occurrences.If the myth lacks any specific scenarios, the Mythbusters will test every reasonable scenario, and just one scenario is enough for them to confirm the myth (for example, when testing to see whether //shooting fish in a barrel// was in fact very easy. In most tests, they could not hit the fish with a bullet, but the energy transfer to the water by the bullet was lethal to the fish). The term "True" was used in the first season.
 * Busted **
 * Plausible **
 * The myth's results can only be replicated by expanding some parameters of the myth by a realistic and reasonable margin. This may have been due to facts of the myth having been altered slightly over time by it being told and re-told by the time it was tested by the MythBusters. Also, certain materials may have had to be substituted for others in some cases as a matter of necessity during the course of the myth being tested, but the new materials are almost always very similar to the materials specified and usually are readily available, so as to prevent it from being prohibitively costly or impractical.
 * If there is not any documentation of the myth occurring, yet the MythBusters were still able to duplicate it very closely to how the myth was described (such as the myth that pirates wore [|eye patches in order to keep their night vision], or a civilian being talked through landing an airplane).
 * If it requires a highly improbable set of circumstances, yet shown to be possible under similar yet artificial circumstances. For example, in the myth of, [|"Can two colliding bullets fuse together?"] it was shown that two bullets can fuse together but would be exceedingly difficult to actually get two period guns with period ammunition to collide in the correct way to cause the result, however the results can be created in a similar laboratory setting.
 * If the results stated in the myth are attainable, but in such a way as to make the process either highly dangerous or less efficient than more common methods of achieving the same result. For example, in "[|Car vs. Rain]", the MythBusters declared the myth "Plausible (but not recommended)", due to the danger in driving a car at high speeds on a wet road even though the myth was completely true.[|[27]]
 * Occasionally a myth will be labelled plausible if the described scenario produces a result similar to, but of less intensity than, the one described in the myth.
 * Confirmed **

Popularity and influence Jamie and Adam as keynote speakers at Symantec Vision 08. Hyneman and Savage have appeared on numerous entertainment programs, such as //[|Good Morning America]//,[|[33]] //[|The Late Show with David Letterman]//,[|[34]] [|NPR]'s news program //[|All Things Considered]//,[|[35]] the syndicated radio //[|Bob and Tom Show]//, and in the movie //[|The Darwin Awards]// (as two military surplus vendors who sold a [|JATO] rocket to the main character). //[|Skeptic]// magazine's [|Daniel Loxton] interviewed the duo in a 2005 article entitled "Mythbusters Exposed."[|[36]] Hyneman and Savage spoke at the annual convention of the [|National Science Teachers Association] in March 2006, and the California Science Teachers Association named them honorary lifetime members in October 2006.[|[37]] They also are occasionally interviewed for articles by //[|Popular Mechanics]// and are featured in that magazine's September 2009 issue.[|[38]] Hyneman and Savage occasionally appear at colleges around the United States to talk about what it's like to be a MythBuster; the show consists of an interview and discussion to give the audience the opportunity to ask the MythBusters questions. The Build Team members have sometimes made appearances in similar capacity. They hold lectures in both collegiate and corporate settings, though the technical colleges tend to be the most enthusiastic.[|[39]][|[40]] They have spoken at [|WPI], [|RPI], [|MIT], [|Georgia Tech], [|Michigan Tech] and many others. Adam Savage and Jamie Hyneman at the [|Discovery Channel]'s Young Scientists Challenge pose with [|Skulls Unlimited International]'s [|Jay Villemarette] and Joey Williams 2004. Adam Savage has written a primer on mold-making for [|//Make// magazine], and was a featured guest at the 2008, 2009, and 2010 [|San Mateo] [|Maker Faire]. Kari Byron was interviewed on //The Late Show//, on January 16, 2006.[|[41]] People involved in survival stories reported in local newscasts have sometimes mentioned previous viewings of //MythBusters// as an influence to their actions. Twenty-three year old Theresa Booth of [|St. Martin, Minnesota] credits a //MythBusters// episode for her and her infant child's survival. On April 3, 2007 she skidded off the road into a drainage ditch which had filled with flood water from the [|Sauk River]. In a local newscast, she is described as opening the car door as soon as it entered the water, and credits her watching of the show (specifically, the episode of [|the Underwater Car myth]) for her knowledge of how to survive the accident.[|[42]] On October 19, 2007 in Sydney, Australia, a teenager named Julian Shaw pulled a fainted middle-aged man off the railway tracks near a train station to safety below the platform. He pulled back as the train passed, citing that [|the "Train Suction" episode] affected his response.[|[43]] On the May 1, 2008 episode of //[|CSI]//, "[|The Theory of Everything]", Hyneman and Savage appeared in a cameo as observers taking notes during a test to determine whether a taser bolt can set someone on fire under various circumstances (They later tested the same thing on Mythbusters). During August 2008, Hyneman and Savage appeared on the stage of [|NVISION 08], an event sponsored by [|Nvidia], having been asked by Nvidia's Creative Director, David Wright, to provide a visual demonstration of the power of the [|GPU] vs a [|CPU]. They did this by creating an image of the [|Mona Lisa] with a giant [|parallel processing] [|paintball] gun, setting a [|world record] for largest paintball gun in the process.[|[44]][|[45]] An encore of the demonstration was given at [|YouTube Live] featuring Hyneman standing in the path of the paintballs wearing a suit of [|armor].[|[46]] Hyneman, Savage, and others from the //MythBusters// crew have appeared at [|The Amaz!ng Meeting], and subsequently were interviewed by Dr. [|Steven Novella] and the "skeptical rogues" for the podcast [|The Skeptics' Guide to the Universe].[|[47]][|[48]] On April 16, 2010, Hyneman and Savage received the Outstanding Lifetime Achievement Award in Cultural Humanism from the Harvard Humanist Chaplaincy.[|[49]] MythBusters at the White House. On October 18, 2010, President Barack Obama, as part of the White House Science Fair, announced he had taped a segment of //MythBusters// and would appear on December 8, 2010. Obama's segment will cover the [|Archimedes] Solar Ray myth.[|[50]][|[51]] Both men appeared at the [|Rally to Restore Sanity and/or Fear] on October 30, 2010 in Washington, D.C. to conduct an experiment with the crowd involving the wave.