Black Holes

Some independent research from one of our RGS Physics pupils:

Black_Hole_Milkyway

The first thing to consider when discussing black holes is the question of exactly what they are. Scientifically, a black hole is defined as ‘A region of space having a gravitational field so intense that no matter or radiation can escape.’

Black holes form when a given mass is compressed within a certain volume. When a large mass fills a very small volume, its density becomes very great due to the equation DENSITY=MASS/VOLUME. When an object becomes dense enough, its gravitational field force becomes so great that not even light can escape.

The exact volume any given mass must be compressed into in order to have the necessary density to become a black hole is called its ‘SCHWARZSCHILD RADIUS’ named after the German physician Karl Schwarzschild. The earth’s Schwarzschild radius is about the size of a peanut.

So what might happen if you were to fall into a black hole?http://www.spacetimetravel.org/expeditionsl/expeditionsl.html  (We’ll work under the presumption that you’re wearing an incredible suit which renders all of the dangers of space completely harmless eg. extremities of temperature, lack of oxygen) The first major point of interest you will reach is called the PHOTON SPHERE. At this exact point upon approaching a black hole, the gravitational field strength of the black hole is just perfect such that light can neither escape from nor be sucked into the hole: instead, light orbits it. At this point in the universe you could theoretically do something which no one on earth has ever done: seen the back of their own head without a mirror. This is because light which reflects off the back of your head orbits the entire black hole and returns to your eye.

The next point of interest is called the EVENT HORIZON. Very basically this is the point of no return. Your eventful and law-defying journey has come to its inevitable climax. Let’s say you’ve brought a friend along to accompany you. When your friend sees you cross the event horizon, they will not in fact see you sucked into the black hole to disappear forever. They will see you actually appear to slow down as you approach it and then freeze upon crossing. Slowly your friend will see your body become more and more REDSHIFTED (red) until it eventually disappears. This is because once you cross the event horizon, light can no longer escape: your friend simply cannot see you any more.

For you however, your journey would continue. Until, unfortunately and inevitably, the incredible gravitational field force of the black hole begins to have more effect on the parts of you close to the hole’s centre than those parts furthest away: you are literally pulled apart in a process called SPAGHETTIFICATION. Try it yourself here :http://hubblesite.org/explore_astronomy/black_holes/encyc_mod3_q16.html

mod3_q16_2

Then what? In truth, nobody knows. Perhaps your individual molecules and atoms would be teleported to another part of the universe through a wormhole?  Perhaps you’ll be crushed into an infinitesimally small volume with an infinite density?   Perhaps you’ll simply disappear into nothingness defying all laws of physics? To be honest, none of these options sounds overly appealing.

SOURCES:

http://hubblesite.org/explore_astronomy/black_holes/

http://en.wikipedia.org/wiki/Black_hole (of course)

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3 thoughts on “Black Holes

  1. How did scientists discover the ‘order of events’ that would take place if you fell into a black hole? Was it theoretically devised and proved using the maths or were any experiments done?

    1. Obviously realistically speaking, the events I’ve described could never happen as you’d be dead long before you approached even the photon sphere. But the sphere itself was calculated mathematically using Newton’s and Einstein’s equations and theories. Knowing the mass and velocity of a photon and the range of masses of a black hole we can calculate that there would be a point whereby photons orbit the hole. (A similar calculation was made for the event horizon- the point whereby light can no longer escape the hole’s pull) Again, similarly, we can calculate that the ‘tidal forces’ (difference of gravitational pull across an object) would be so great as to be able to pull a body apart. Stephen Hawking developed these ideas and writes about them to a fair extent in ‘A Brief History of Time’. As for experiments, the nearest black hole is called V4641 Sagittarii and it’s 1600 light years away. This makes it (fairly obviously) quite difficult to experiment on.

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