# The Naked Scientists Forum

### Author Topic: How to measure Black Holes?  (Read 2041 times)

#### J Rahman

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• Truth is my passion, and my passion can lead me (and you too) to the Ultimate Truth... atleast I hope so!
##### How to measure Black Holes?
« on: 07/11/2009 03:49:11 »
What technique is used to measure the radius of the event horizon of a black hole? Is there any formula? If so, then please let me know.

Secondly I would like to ask whether the event horizons are of the same size for all black holes or they are of varying sizes: some big and some small?

Finally, I would like to ask whether it would be wise for Newton, if he were a member of this forum, to publish his laws of motion here or somewhere else in the internet (such as blogger)? What I'm asking is how safe it is to publish catastrophic theories (not hypothesis) in the internet? Can Newton get rid of the thought of someone stealing his 'Principia' ? What should I do if I make some discovery?

#### Mr. Scientist

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##### How to measure Black Holes?
« Reply #1 on: 08/11/2009 14:25:17 »
First, let us assume the following > M is for mass, R is for radius, D is for density and V is for volume. The radius of a thing like a black hole has proportional relationships.

The radius of a balck hole is found to be directly proportional to its mass.

(R- M)

The density of a black hole is given by its mass divided by its volume,

(D=M/V)

... and since the volume is proportional to the radius of the black hole to the power of three,

(V- R^3)

... then the density of the black hole is inversely proportional to its mass raised by the second power.

(D- M^2)

The event horizon is simply a boundary of a black hole. You can work out specific radius calculatuions, such as a killing horizon which has a radius of r=\sqrt 3/lambda. There is what is called a Schwarzschild radius - this is an area which acts like an event horizon. The characteristics are associated to the quantity of mass.

Where r is radius, G is Newtons gravitational constant, c is lightspeed the radius is found:

r=2GM/c^2

#### Mr. Scientist

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##### How to measure Black Holes?
« Reply #2 on: 08/11/2009 14:25:46 »
(and yeh) - they vary.

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##### How to measure Black Holes?
« Reply #3 on: 08/11/2009 17:42:22 »
Wouldn't the angular velocity also effect its density/volume/radius?

#### Mr. Scientist

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##### How to measure Black Holes?
« Reply #4 on: 09/11/2009 15:42:04 »
Wouldn't the angular velocity also effect its density/volume/radius?

Essentially, Velocity of angular momentum does in fact alter the shape of a black hole, by theory, though it should not in general alter its instrinsic density.

#### Soul Surfer

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##### How to measure Black Holes?
« Reply #5 on: 11/11/2009 08:59:04 »
To find the size and properies of of do it yourself black holes go to

http://xaonon.dyndns.org/hawking/

You will fond that a solar mass black hole is about a mile across and as the size is a linear function of its mass a billion solar mass black hole (the sort that are in the largest elliptical galaxies) is about as big as the orbit of Uranus and a one million solar mass black hole like the one in our galaxy is a bit bigger than the sun.

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##### How to measure Black Holes?
« Reply #5 on: 11/11/2009 08:59:04 »