what is a black hole?

Question

I have alwas been interested in astronomy and would like a complete detail information on it. Please anwer the question OR refer to a website.
Thank You

Answer 1

Any mass contained in a radius smaller than its schwarzschild radius,

r_s = (2GM/c^2) with

c= the speed of light, G = the gravitational constant and M is the mass of the object.

The schwarzschild radius scales linearally with mass (an object twice as massive will have twice the schwarzschild radius) and to get you started, an object the mass of the sun (2x10^30kg) has a Schwarzschild radius of 3 km. In otherwords, if you jammed the sun into a sphere 6km across, it would be a black hole. The schwarzschild radius indicates a volume of space where the escape velocity from the mass in question is the speed of light or greater. Using the linear scaling, an object the mass of the earth (6(?)x10^24 kg would have a schwarzschild radius of about 1/300,000 of 3km, or 1 cm.

Black holes have some peculiar properties, such as evaporation, extremely strong tidal forces near their central singularity (but weak tidal forces at the schwarzschild radius of a supermassive black hole). Things can happen inside of the schwarzschild radius too. For instance, if our universe was closed (not expanding enough to continue expanding forever) it is technically inside of its own schwarzschild radius (we would be living inside a huge black hole.)

It is called a black hole because no light that crosses the schwarzschild radius can completely escape the mass to an infinite distance. (This does mean that if you are just outside the schwarzschild radius yourself, you CAN see light that is emitted from within it, or passes within it as long as it is not too close; only an observer at d= infinity cannot.) Thus this volume of space appears "black." You can read more about black holes on wikipedia at http://en.wikipedia.org/wiki/black_hole....

The concept of an object with gravity so great was first conceived by a little known geologist named John Michell. The better known Simon Laplace took the idea and ran with it in a book years later and so is often credited with coming up with the idea.

Answer 2

A black hole is the remanants of a massive star that has collapsed to a very dense object and its surface gravity is so strong that even light cannot escape.

A black hole doesn't posses any more mass than the normal star it was formed out of and from far distances (like if a planet was orbiting it) the gravity wouldn't act any differently.

Normal stars limit there density and maintain their size by the fusion reaction (turning hydrogen to helium) balancing the gravitational pull. When the hydrogen runs out in the core (the only place hot enough to fuse hydrogen to helium) the star collapses and a new reaction starts (turning helium into a heavier element). The star keeps on fusing heavier elements until it forms an iron core that will not fuse into a heavier element. The star collapses, then springs back in a supernova.

One of three things happen after a supernova:

1) The star loses the majority of its mass and becomes a nebula.

2) The star retains most of its mass (Below 1.44 solar masses) and collapses to the size of a small planet, squishing electrons and protons together to become a neutron star. Mutual repulsion of the matter balance the crushing forces of gravity.

3) The star retains most of its mass (above 1.44 solar mass) and collapses. Mutual repulsion isn't enough to couteract gravity since the matter would have to be moving at the speed of light to produce enough repulsion. So the star collapses further into a black hole.

Answer 3

A black hole is a mathematical explanation of mysterious x ray emitting points in the universe. Scientists have found areas in space that emits x rays but could not find the source.

So their explanation was that, there are places in the space where the gravitational pull is so high and thus all matter around that point are sucked in to that place. They believe that these places are actually energy remains of dead stars. ( Remember that in stars matter is converted in to energy and since energy can not be destroyed when the star dies it is converted to gravity)

The gravitational pull is so high at these points ( the mathematical centre of a black hole is called the singularity) it makes the matter run around and round and thus heated to very high heat. Up to the heat that is exceeds the light emitting stage and start emitting x rays. These are the x rays that scientists observed.

The reason why they called it a black hole is that neither light can pass this places with out being sucked in. Remember that light is after all photons which have a mass and thus it is matter.

This is all mathematical and based highly on quantum mechanics. So, I guess that only Einstein and Max Planck would totally understand this and believe this

Answer 4

A black hole is a region of spacetime from which nothing can escape, even light.

To see why this happens, imagine throwing a tennis ball into the air. The harder you throw the tennis ball, the faster it is travelling when it leaves your hand and the higher the ball will go before turning back. If you throw it hard enough it will never return, the gravitational attraction will not be able to pull it back down. The velocity the ball must have to escape is known as the escape velocity and for the earth is about 7 miles a second.

As a body is crushed into a smaller and smaller volume, the gravitational attraction increases, and hence the escape velocity gets bigger. Things have to be thrown harder and harder to escape. Eventually a point is reached when even light, which travels at 186 thousand miles a second, is not travelling fast enough to escape. At this point, nothing can get out as nothing can travel faster than light. This is a black hole.

Source:
http://www.damtp.cam.ac.uk/user/gr/public/bh_intro.html

Answer 5

Let's think about the answers we give before you answer them. A black hole is not necessarily black. Light does escape from a black hole. Black holes event horizon radiates energy,a black hole has a temperature then why would it radiate x-rays into space. A black hole does not need to be a star with 3 solar massse to collapse into it's self. If the earth could be squeezed to the sized of a M&M it would be a black hole. Anything could be a black hole if you can make it's mass sufficiently small.

Answer 6

I'm surprised no one used the word vortex yet.

But anyways... a black hole is simply a vortex with unlimited length in its... swirly thing.

The death of stars are caused by black holes. A small black hole can pull in a star bigger than our sun because in this hole, there is a vacuum so strong. After that? No one knows for sure. We simply say that it disappears.

And yes, a black hole is visible. It looks the opposite of a star, a dark eliptical shadow that moves across the universe.

~Ninth Grader

Answer 7

it's not filled with smoke!
A black hole is an object predicted by general relativity[1] with a gravitational field so strong that nothing can escape it — not even light. http://en.wikipedia.org/wiki/Black_hole
so, it's just an object with an EXTREMELY strong gravity field
also, see quasar, which is a galaxy with a black hole in the middle.
http://en.wikipedia.org/wiki/Quasar

Answer 8

Black hole creates after the supernova of star it must have 1.5 mass bigger then sun.In every galaxy there is a black hole.In the center is the biggest black hole.There are quasars in the biggest black holes.1000 times bigger then main black hole in the center of our galaxyhttp://www.phys.vt.edu/~jhs/faq/quasars.html#q1

Answer 9

its a hole black full of smoke that sucks in gravity in its path

Answer 10

well, first, you start with a nubian princess....