Hershey wrote::?
i bit too many advanced words for me >< lol very interesting though
cant wait for that black holes theory..^^
Ya ill be posting those right now:
Black Holes (2nd fav QP topic)
INTRO To BH's:
A black hole is an object with a gravitational field so powerful that a region of space becomes cut off from the rest of the universe – no matter or radiation, including visible light, that has entered the region can ever escape. The lack of escaping electromagnetic radiation renders the inside of black holes (beyond the event horizon) invisible, hence the name. However, black holes can be detectable if they interact with matter, e.g. by sucking in gas from an orbiting star. The gas spirals inward, heating up to very high temperatures and emitting large amounts of light, X-rays and Gamma rays in the process while still outside of the event horizon. Black holes are also thought to emit a weak form of thermal energy called Hawking radiation.
While the idea of an object with gravity strong enough to prevent light from escaping was proposed in the 18th century, black holes as presently understood are described by Einstein's theory of general relativity, developed in 1916. This theory predicts that when a large enough amount of mass is present within a sufficiently small region of space, all paths through space are warped inwards towards the center of the volume. When an object is compressed enough for this to occur, collapse is unavoidable (it would take infinite strength to resist collapsing into a black hole). When an object passes within the event horizon at the boundary of the black hole, it is lost forever (it would take an infinite amount of effort for an object to climb out from inside the hole). Although the object would be reduced to a singularity, the information it carries is not lost (see the black hole information paradox).
While general relativity describes a black hole as a region of empty space with a pointlike singularity at the center and an event horizon at the outer edge, the description changes when the effects of quantum mechanics are taken into account. The final, correct description of black holes, requiring a theory of quantum gravity, is unknown.
BLACK HOLES!
Event horizon
This is the boundary of the region from which not even light can escape. An observer at a safe distance would see a dull black sphere if the black hole was in a pure vacuum but in front of a light background such as a bright nebula. The event horizon is not a solid surface, and does not obstruct or slow down matter or radiation which is traveling towards the region within the event horizon.
The event horizon is the defining feature of a black hole - it is black because no light or other radiation can escape from inside it. So the event horizon hides whatever happens inside it and we can only calculate what happens by using the best theory available, which at present is general relativity.
The gravitational field outside the event horizon is identical to the field produced by any other spherically symmetric object of the same mass. The popular conception of black holes as "sucking" things in is false: objects can maintain an orbit around black holes indefinitely provided they stay outside the photon sphere (described below).
Singularity at a single point
According to general relativity, a black hole's mass is entirely compressed into a region with zero volume, which means its density and gravitational pull are infinite, and so is the curvature of space-time which it causes. These infinite values cause most physical equations, including those of general relativity, to stop working at the center of a black hole. So physicists call the zero-volume, infinitely dense region at the center of a black hole a "singularity".
The singularity in a non-rotating, uncharged black hole is a point, in other words it has zero length, width and height.
But there is an important uncertainty about this description: quantum mechanics is as well-supported by mathematics and experimental evidence as general relativity, and does not allow objects to have zero size - so quantum mechanics says the center of a black hole is not a singularity but just a very large mass compressed into the smallest possible volume. At present we have no well-established theory which combines quantum mechanics and general relativity; and the most promising candidate, string theory, also does not allow objects to have zero size.
The rest of this article will follow the predictions of general relativity, because quantum mechanics deals with very small-scale (sub-atomic) phenomena and general relativity is the best theory we have at present for explaining large-scale phenomena such as the behavior of masses similar to or larger than stars.
A photon sphere
A non-rotating black hole's photon sphere is a spherical boundary of zero thickness such that photons moving along tangents to the sphere will be trapped in a circular orbit. For non-rotating black holes, the photon sphere has a radius 1.5 times larger than the radius of the event horizon. No photon is likely to stay in this orbit for long, for two reasons. First, it is likely to interact with any infalling matter in the vicinity (being absorbed or scattered). Second, the orbit is dynamically unstable; small deviations from a perfectly circular path will grow into larger deviations very quickly, causing the photon to either escape or fall into the hole.
Other extremely compact objects such as neutron stars can also have photon spheres. This follows from the fact that light "captured" by a photon sphere does not pass within the radius that would form the event horizon if the object were a black hole of the same mass, and therefore its behavior does not depend on the presence of an event horizon.
Accretion disk
Space is not a pure vacuum - even interstellar space contains a few atoms of hydrogen per cubic centimeter. The powerful gravity field of a black hole pulls this towards and then into the black hole. The gas nearest the event horizon forms a disk and, at this short range, the black hole's gravity is strong enough to compress the gas to a relatively high density. The pressure, friction and other mechanisms within the disk generate enormous energy - in fact they convert matter to energy more efficiently than the nuclear fusion processes that power stars. As a result, the disk glows very brightly, although disks around black holes radiate mainly X-rays rather than visible light.
Accretion disks are not proof of the presence of black holes, because other massive, ultra-dense objects such as neutron stars and white dwarfs cause accretion disks to form and to behave in the same ways as those around black holes.
OH NOES IM FALLING INTO A BH SECTION
Spaghettification
An object in any very strong gravitational field feels a tidal force stretching it in the direction of the object generating the gravitational field. This is because the inverse square law causes nearer parts of the stretched object to feel a stronger attraction than farther parts. Near black holes, the tidal force is expected to be strong enough to deform any object falling into it; this is called spaghettification.
The strength of the tidal force depends on how gravitational attraction changes with distance, rather than on the absolute force being felt. This means that small black holes cause spaghettification while infalling objects are still outside their event horizons, whereas objects falling into large, supermassive black holes may not be deformed or otherwise feel excessively large forces before passing the event horizon.
Before the falling object crosses the event horizon
An object in a gravitational field experiences a slowing down of time, called gravitational time dilation, relative to observers outside the field. The observer will see that physical processes in the object, including clocks, appear to run slowly. As a test object approaches the event horizon, its gravitational time dilation (as measured by an observer far from the hole) would approach infinity.
From the viewpoint of a distant observer, an object falling into a black hole appears to slow down, approaching but never quite reaching the event horizon: and it appears to become redder and dimmer, because of the extreme gravitational red shift caused by the gravity of the black hole. Eventually, the falling object becomes so dim that it can no longer be seen, at a point just before it reaches the event horizon. All of this is a consequence of time dilation: the object's movement is one of the processes that appear to run slower and slower, and the time dilation effect is more significant than the acceleration due to gravity; the frequency of light from the object appears to decrease, making it look redder, because the light appears to complete fewer cycles per "tick" of the observer's clock; lower-frequency light has less energy and therefore appears dimmer.
From the viewpoint of the falling object, distant objects may appear either blue-shifted or red-shifted, depending on the falling object's trajectory. Light is blue-shifted by the gravity of the black hole, but is red-shifted by the velocity of the infalling object.
As the object passes through the event horizon
From the viewpoint of the falling object, nothing particularly special happens at the event horizon (apart from spaghettification due to tidal forces, if the black hole has relatively low mass). A falling observer would measure a non-infinite amount of time (in their reference frame) needed to fall past the point where the event horizon is supposed to be.
An outside observer, however, will never see an infalling object cross this line. The object appears to halt just above the horizon, due to gravitational time dilation, fading from view as its light is red-shifted and the rate at which it emits photons drops to approach zero. This doesn't mean that the object never crosses the horizon; instead, it means that light from the horizon-crossing event is delayed by a time that approaches infinity as the object approaches the horizon. The time of crossing depends on how the outside observer chooses to define space and time axes on spacetime near the horizon.
In practice, additional effects are expected to occur as an object approaches the event horizon of a black hole. Hawking radiation is expected to grow brighter, approaching the Planck temperature as an infalling object approaches to within the Planck length of the horizon. Both relativistic and quantum mechanical effects may present a backwards pressure that approaches infinite strength near the horizon, making the fate of infalling objects unclear. This type of back-pressure may cause the region near or within the event horizon to be at very high temperature. As of 2007, there is no scientific consensus about what happens as objects fall into black holes, beyond the fact that it's expected to differ from the picture described by general relativity.
Inside the event horizon
The object reaches the singularity at the center within a finite amount of proper time, as measured by the falling object. An observer on the falling object would continue to see objects outside the event horizon, blue-shifted or red-shifted depending on the falling object's trajectory. Objects closer to the singularity aren't seen, as all paths light could take from objects farther in point inwards towards the singularity.
The amount of proper time a faller experiences below the event horizon depends upon where they started from rest, with the maximum being for someone who starts from rest at the event horizon. A study in 2007 examined the effect of firing a rocket pack with the black hole, showing that this can only reduce the proper time of a person who starts from rest at the event horizon. However, for anyone else, a judical burst of the rocket can extend the life time of the faller, but over doing it will again reduce the proper time experienced. However, this cannot prevent the inevitable collision with the central singularity.
Hitting the singularity
As a infalling object approaches the singularity, tidal forces acting on it approach infinity. All components of the object, including atoms and subatomic particles, are torn away from each other before striking the singularity. At the singularity itself, effects are unknown; a theory of quantum gravity is needed to accurately describe events near it. Regardless, as soon as an object passes within the hole's event horizon, it is lost to the outside world. An observer far from the hole simply sees the hole's mass, charge, and angular momentum change to reflect the addition of the new object's matter.
ENJOY! Worm holes to come next.<<banned from SRF for rules violations. -SG>>
hmm some strange blabla ρ = 3c^6/ 32πm²G³
