Black Holes: Difference between revisions

 

{{quote|''Consideration of black holes suggests, not only that God does play dice, but that He sometimes confuses us by throwing them where they can't be seen.''|'''[[Stephen Hawking]]''', ''The Nature of Space and Time''}}

 

''And it is getting closer.''|RobotRollCall, [http://www.reddit.com/r/askscience/comments/f1lgu/what_would_happen_if_the_event_horizons_of_two/ here].}}

 

Stars convert hydrogen into helium via fusion, which produces enormous amounts of energy. This energy keeps the core from collapsing. However, when the star ages, the hydrogen runs out. Stars of sufficient mass can fuse helium into heavier elements (turning into red giants), but even that can't go on forever; producing elements heavier than iron uses energy instead of producing it. So at some point the star runs out of fuel and collapses.

 

 

Black holes can form from masses smaller than stars if the mass is under enough pressure, producing a "micro black hole", but this may require exotic physical conditions such as the ones existing right after the Big Bang.

 

 

In fact, space-time will become quite freaky around the event horizon: the closer you get to the event horizon, the [[Year Inside, Hour Outside|slower time becomes]] (due to relativity, however, you won't notice it). In fact, if an observer outside the event horizon could see you, they would see as you get closer and closer (and get redder, due to gravitation red shift, while everything you see would be bluer), you would go slower and slower until you hit the edge of the event horizon at which point you would ''stop'' (nobody would actually see you hit the event horizon, since you appear to slow down as you get closer, for an outside observer, you would take an infinite amount of time to reach it. You wouldn't actually stop, that's just what they'll see). This prediction, however, assumes zero mass of incoming object and neglect quantum effects, so reality may be more tricky.

 

 

However, you'd probably be long dead before that anyway as black holes come with some dangers attached due to the extremely intense gravity around them: First, you'll be spaghettified (this ''is'' the scientific term for it); the tidal forces of the black hole are so strong that, if you were going in feet first, your feet would feel a stronger attraction than your head and thus your body would stretch out (incidentally, this occurs in more applicable situations, such as returning space shuttles, as well - the difference is that the attraction difference is so minor that the astronauts do not stretch a measurable amount). The gravity exerted by black holes is so strong that it can even deform atoms. On the upside, the bigger a black hole is, the less drastic this effect becomes on its edge; in fact, for a supermassive black hole, an individual should survive at least past the event horizon. The second big danger is good old radiation, due to gravitational blueshifting. Any radiation hitting you from the outside would be blueshifted (given higher frequencies, and therefore energy, as opposed to redshifting, which decreases the frequency of electromagnetic radiation and therefore their energy) and thus a lot more dangerous, to the point that, [http://jila.colorado.edu/~ajsh/insidebh/realistic.html according to some simulations], it would be the thing that would kill you before you could reach the singularity, assuming a black hole big enough to neglect tidal effects. It's known as [http://discovermagazine.com/2011/jun/26-strange-physics-singular-views-inside-black-holes/article_view?b_start:int=2&-C= ''inflationary instability''] and, according to scientists, [[There Is No Kill Like Overkill|its effects would go very far beyond of just vaporizing your body.]]

A black hole's size -- that is, the radius of its event horizon -- depends on its mass, spin, and charge. The simplest case of an uncharged, non-spinning ("Schwarzchild") black hole has a surprisingly straightforward formula:

 

 

And for astrophysics, this is more than sufficient to get a ballpark estimate of the size of any black hole based on the mass it contains. Thus, a black hole with a mass equal to the sun has an event horizon 3 kilometers in radius (6 km in diameter).

 

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[[Category:Black Holes]]