How scientist measure the gravitational pull of a body.for ex they say that black holes have large pull how?

Answer 1

Black holes bend light. Astronomers can measure the bending effect to determine the location of the lack hole.

Answer 2

If something (say a star) is rotating around a black hole, the centrifugal acceleration is
4 pi^2 r /T^2
where T is the time it takes to cycle the orbit and r is the radius of the orbit.
For the orbit to be circular, this must be equal to the gravitational acceleration
MG/r^2
where G is the gravitational constant (can be measured in a lab) and M is the mass of the black hole.

If r and T are known, you can solve the equation
MG/r^2=4 pi^2 r /T^2:

M = 4 pi^2 r^3/(GT^2)

With more advanced math you can do the same for non-circular movements. The orbitting object does not have to be a star. It could also be light, as the first answerer said.

Answer 3

Scientists figure out the mass of an object by the effect it has on the matter that surrounds it. The greater the object in size, the more mass it has, the greater the effect of that objects gravity will have on the surrounding matter. Black holes on the other hand are infinitly small and infinitly dense. Even though you cannot see a black hole you can observe it's effects on the surrounding matter. It's a matter of physics. Gravity isn't actually created by the mass of the object though. The mass of the object actually causes space to warp around it. If you stretch a rubber sheet and place a bolling ball on it you can see how the sheet gets stretche by the mass of the ball. The same thing happens with space. Hope this helps.
Cheers!

Answer 4

If we know the orbit of a body near by we could calculate the gravity of the pulling body. For example if on from outer space measure the orbit of the moon ( difficult to observe because it doesn't have its own light) then from the orbital data one can calculate the earths gravity. Black holes are more often the center of galaxies so stars orbit around them. Stars are easy to observe.

Note: If one knows the orbit the gravity can be calculated without knowing the mass. ( I have to refresh on this. Studied long time ago) roughly

(mv^2/2) * r = mg

that is centrifugal force = weight

m cancels.
v^2 =2 g*r

But actual calculations are more complex because one has to adjust for the decay of gravity with altitude and the orbit are seldom circular. mostly elliptical. I Will leave that for a more reading on the subject

Answer 5

Einstein made a mistake in thinking that an accelerating mass had an addition of mass added to it in form of energy. It is because of this mistake that black holes, and the big bang exist. Moving mass transforms the overall frequency of the mass into a single dimension. This happens at a proportional reduction of frequency at right angles to the direction of movement.

The concept for this is a bit different. It is found in a frequency trilogy:

E = hf, is that for electromagnetic energy.

mk = hf, describes why mass frequency changes with movement. In that mass is made up of electromagnetic energy, it is under the same value. The greater the energy in a particular direction - the greater the line density/frequency.

c = hf, is that for a graviton [c(g)].

There is a writing at http://360.yahoo.com/noddarc that explains this. It is entitled, "The Problem and Repair of Relativity).

Answer 6

They do this by observing the black hole's (or other object's) effect on a body of a known size.

Answer 7

because black hole has a capablitiy to even absorb light. dats y dey cnt b detected. they enormous mass n gravitational pull