Sub-Orbital Space Flights & Exploration
Well from my understanding, when things pulled into a black hole after a Sun in a galaxy explodes, they are compressed to microscopic sizes. That's what my science proffessor says at least. Well what happens then to the galaxy? Does the black hole just stay there or what? Any info on black holes or astronomy would be of much help.
It stays there until it can start sucking other stuff up in the vicinity.
http://en.wikipedia.org/wiki/Black_Hole
The black hole continues to suck in as much matter as it can, but even the largest Super Massive Black Holes have a limited raidius which they can suck in. They are about the size of 5-12 kilometers, only stars with a mass of over 3 can turn into a black hole. The black hole pretty much just stays there sucking everything it can take, which is only a limited radius like I said. =)
http://news.yahoo.com/s/space/20060424/sc_space/blackholesareactuallygreen
the edge of a black hole is called the event horizon. anything outside it is able to escape the black hole. anything inside it will be sucked in by the black hole.
black hole just keep sucking matter in, and the in-falling matter causes the BH to spin, creating a magnetic field. the matter is somehow converted to radition that is emitted at the north and south poles of the spin. so basically what goes in can come out as radiation.
Black holes are wild. When a dead sun of sufficient mass collapses, at a certain point (critical mass) the material is so dense that it essentially disapears. It becomes a point in space (no width, depth, or height). Where did this mass go? It was converted to a permanent deformation of space. It is a hole that looks as if there is a mass there. Just as a rocket needs an escape velocity to leave the Earth, the black hole has an escape velocity that is greater than the speed of light. This means that nothing can escape it. That’s why we call them black holes. They can swallow more matter and get even bigger. It has been determined that most galaxies have super massive black holes in there centers. Often black holes are seen with companion stars and they are sucking matter into them from the nearby sun. That is how we find a lot of them.
Black holes suck in matter in the nearby vicinity, but their gravitational field is not strong enough to sause an entire galaxy to collapse.
A black hole is a concentration of mass great enough that the force of gravity prevents anything past its event horizon from escaping it except through quantum tunnelling behaviour (known as Hawking Radiation). The gravitational field is so strong that the escape velocity past its event horizon exceeds the speed of light. This implies that nothing, not even light, inside the event horizon can escape its gravity. It is, however, theorized that wormholes can let one exit a black hole. The term “black hole” is widespread, even though it does not refer to a hole in the usual sense, but rather a region of space from which nothing can return.
The existence of black holes in the universe is well supported by astronomical observation, particularly from studying X-ray emission from X-ray binaries and active galactic nuclei.
Formation
General relativity (as well as most other metric theories of gravity) not only says that black holes can exist, but in fact predicts that they will be formed in nature whenever a sufficient amount of mass gets packed in a given region of space, through a process called gravitational collapse. For example, if you compressed the Sun to a radius of three kilometers, about four millionths of its present size, it would become a black hole. As the mass inside the given region of space increases, its gravity becomes stronger — or, in the language of relativity, the space around it becomes increasingly deformed. Eventually gravity gets so strong that nothing can escape; an event horizon is formed, and matter and energy must inevitably collapse into a singularity.
A quantitative analysis of this idea led to the prediction that a stellar remnant above about three to five times the mass of the Sun (the Tolman-Oppenheimer-Volkoff limit) would be unable to support itself as a neutron star via degeneracy pressure, and would inevitably collapse into a black hole. Stellar remnants with this mass are expected to be produced immediately at the end of the lives of stars that are more than 25 to 50 times the mass of the Sun, or by accretion of matter onto an existing neutron star.
Stellar collapse will generate black holes containing at least three solar masses. Black holes smaller than this limit can only be created if their matter is subjected to sufficient pressure from some source other than self-gravitation. The enormous pressures needed for this are thought to have existed in the very early stages of the universe, possibly creating primordial black holes which could have masses smaller than that of the Sun.
Supermassive black holes are believed to exist in the center of most galaxies, including our own Milky Way. This type of black hole contains millions to billions of solar masses, and there are several models of how they might have been formed. The first is via gravitational collapse of a dense cluster of stars. A second is by large amounts of mass accreting onto a “seed” black hole of stellar mass. A third is by repeated fusion of smaller black holes.
Intermediate-mass black holes have a mass between that of stellar and supermassive black holes, typically in the range of thousands of solar masses. Intermediate-mass black holes have been proposed as a possible power source for ultra-luminous X ray sources, and in 2004 detection was claimed of an intermediate-mass black hole orbiting the Sagittarius A* supermassive black hole candidate at the core of the Milky Way galaxy. This detection is disputed.
Certain models of unification of the four fundamental forces allow the formation of micro black holes under laboratory conditions. These postulate that the energy at which gravity is unified with the other forces is comparable to the energy at which the other three are unified, as opposed to being the Planck energy (which is much higher). This would allow production of extremely short-lived black holes in terrestrial particle accelerators. No conclusive evidence of this type of black hole production has been presented, though even a negative result improves constraints on compactification of extra dimensions from string theory or other models of physics.
The “surface” of a black hole is the so-called event horizon, an imaginary surface surrounding the mass of the black hole. Stephen Hawking proved that the topology of the event horizon of a non-spinning black hole is a sphere. At the event horizon, the escape velocity is equal to the speed of light. Thus, anything inside the event horizon, including a photon, is prevented from escaping across the event horizon by the extremely strong gravitational field. Particles from outside this region can fall in, cross the event horizon, and will never be able to leave.
Since external observers cannot probe the interior of a black hole, according to classical general relativity, black holes can be entirely characterised according to three parameters: mass, angular momentum, and electric charge. This principle is summarised by the saying, coined by John Wheeler, “black holes have no hair” meaning that there are no features that distinguish one black hole from another, other than mass, charge, and angular momentum.
Objects in a gravitational field experience a slowing down of time, called time dilation. This phenomenon has been verified experimentally in the Scout rocket experiment of 1976,[9] and is, for example, taken into account in the GPS system. Near the event horizon, the time dilation increases rapidly. To the distant observer, a falling object’s movement slows down, approaches but never reaches the event horizon. Any escaping photons do not slow down when escaping the gravity well but experience redshifting. From the falling object’s frame of reference, it will cross the event horizon and reach the singularity, at the centre of the black hole within a finite amount of time.
Spacetime inside the event horizon of an uncharged non-rotating black hole is peculiar in that the singularity is in every observer’s future, so all particles within the event horizon move inexorably towards it (Penrose and Hawking). This means that there is a conceptual inaccuracy in the non-relativistic concept of a black hole as originally proposed by John Michell in 1783. In Michell’s theory, the escape velocity equals the speed of light, but it would still, for example, be theoretically possible to hoist an object out of a black hole using a rope. General relativity eliminates such loopholes, because once an object is inside the event horizon, its time-line contains an end-point to time itself, and no possible world-lines come back out through the event horizon. A consequence of this is that a pilot in a powerful rocket ship that had just crossed the event horizon who tried to accelerate away from the singularity would reach it sooner in his frame, since geodesics (unaccelerated paths) are paths that maximise proper time.[10]
As the object continues to approach the singularity, it will be stretched radially with respect to the black hole and compressed in directions perpendicular to this axis. This phenomenon, called spaghettification, occurs as a result of tidal forces: the parts of the object closer to the singularity feel a stronger pull towards it (causing stretching along the axis), and all parts are pulled in the direction of the singularity, which is only aligned with the object’s average motion along the axis of the object (causing compression towards the axis).
At the centre of the black hole, well inside the event horizon, general relativity predicts a singularity, a place where the curvature of spacetime becomes infinite and gravitational forces become infinitely strong.
It is expected that future refinements or generalisations of general relativity (in particular quantum gravity) will change what is thought about the nature of black hole interiors. Most theorists interpret the mathematical singularity of the equations as indicating that the current theory is not complete, and that new phenomena must come into play as one approaches the singularity.[11]
The cosmic censorship hypothesis asserts that there are no naked singularities in general relativity. This hypothesis is that every singularity is hidden behind an event horizon and cannot be probed. Whether this hypothesis be true remains an active area of theoretical research.
Another school of thought holds that no singularity occurs, because of a bubble-like local inflation in the interior of the collapsing star.[12] Radii stop converging as they approach the event horizon, are parallel at the horizon, and begin diverging in the interior. The solution resembles a wormhole (from the exterior to the interior) in a neighborhood of the horizon, with the horizon as the neck.
According to theory, the event horizon of a black hole that is not spinning is spherical, and its singularity is (informally speaking) a single point. If the black hole carries angular momentum (inherited from a star that is spinning at the time of its collapse), it begins to drag space-time surrounding the event horizon in an effect known as frame-dragging. This spinning area surrounding the event horizon is called the ergosphere and has an ellipsoidal shape. Since the ergosphere is located outside the event horizon, objects can exist within the ergosphere without falling into the hole. However, because space-time itself is moving in the ergosphere, it is impossible for objects to remain in a fixed position. Objects grazing the ergosphere could in some circumstances be catapulted outwards at great speed, extracting energy (and angular momentum) from the hole, hence the name ergosphere (”sphere of work”) because it is capable of doing work.
The singularity inside a rotating black hole is a ring. It is possible for an observer to avoid hitting this singularity, for example, proceeding along the black hole spin axis; however, it is still not possible to escape the black hole’s event horizon.
In 1971, Stephen Hawking showed that the total area of the event horizons of any collection of classical black holes can never decrease. This sounded remarkably similar to the Second Law of Thermodynamics, with area playing the role of entropy. Classically, one could violate the second law of thermodynamics by material entering a black hole disappearing from our universe and resulting in a decrease of the total entropy of the universe. Therefore, Jacob Bekenstein proposed that a black hole should have an entropy and that it should be proportional to its horizon area. Since black holes do not classically emit radiation, the thermodynamic viewpoint was simply an analogy. However, in 1974, Hawking applied quantum field theory to the curved spacetime around the event horizon and discovered that black holes can emit Hawking radiation, a form of thermal radiation. Using the first law of black hole mechanics, it follows that the entropy of a black hole is one quarter of the area of the horizon. This is a universal result and can be extended to apply to cosmological horizons such as in de Sitter space. It was later suggested that black holes are maximum-entropy objects, meaning that the maximum entropy of a region of space is the entropy of the largest black hole that can fit into it. This led to the holographic principle.
Hawking radiation originates just outside the event horizon and, so far as it is understood, does not carry information from its interior since it is thermal. However, this means that black holes are not completely black: the effect implies that the mass of a black hole slowly evaporates with time. Although these effects are negligible for astronomical black holes, they are significant for hypothetical very small black holes where quantum-mechanical effects dominate. Indeed, small black holes are predicted to undergo runaway evaporation and eventually vanish in a burst of radiation. Hence, every black hole that cannot consume new mass has a finite life that is directly related to its mass.
An open question in fundamental physics is the so-called information loss paradox, or black hole unitarity paradox. Classically, the laws of physics are the same run forward or in reverse. That is, if the position and velocity of every particle in the universe were measured, we could (disregarding chaos) work backwards to discover the history of the universe arbitrarily far in the past. In quantum mechanics, this corresponds to a vital property called unitarity which has to do with the conservation of probability.
Black holes, however, violate this rule. Because of the no hair theorem, we can never determine what went into the black hole. Information is apparently destroyed, as there is no way to reconstruct what went into the black hole. This is an important unsolved conceptual problem in quantum gravity.
On 21 July 2004 Stephen Hawking presented a new argument that black holes do eventually emit information about what they swallow, reversing his previous position on information loss. He proposed that quantum perturbations of the event horizon could allow information to escape from a black hole, where it can influence subsequent Hawking radiation.[13] The theory has not yet been reviewed by the scientific community, and if it is accepted it is likely to resolve the black hole information paradox. In the meantime, the announcement has attracted a lot of attention in the media.