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/sci/ - Science & Math

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3007255 No.3007255 [Reply] [Original]

If a light source was directed perpendicular to the plane which is tangent to a point on the radius of the sphere where the escape velocity of a black hole is equal to the speed of light, would the light from it go into orbit?

Another, maybe simpler way of putting it:
If a light source is directed opposite the centre AT the Schwarzschild radius of a black hole would it go into orbit, just be stationary, or would something else happen?

>> No.3007258

>>3007255
I meant surface of the sphere, not radius.

>> No.3007278

>>3007255
My phrasing was shit, I will rephrase yet again.

If I shone a light beam away from the singularity at the event horizon of a black hole what would happen?

>> No.3007296

I dont know if it will go into orbit, but light wont stay in orbit around a black hole because its to unstable, it will fall into the black hole or escape before making a complete orbit.

capcha: Einstein forkeryw

>> No.3007354

>>3007296
What do you mean by unstable?
If an object is kept at a fixed distance away in the gravitational field, moving around in circular motion then it's in orbit no?
Assuming that the light wasn't "disturbed" by anything else would it be able to remain in this state?
Is it even possible to have stationary light?

>> No.3007449

Bump for answer (if there is one).

>> No.3007471

I would think the light would orbit the black hole, but Im just an undergrad so Im likely horribly wrong

ask this question next time physics guy has a q&a thread, it would be interesting.

>> No.3007476

>>3007471
I will, my physics tutor didn't have a clue and didn't even seem interested to be honest.
Maybe someone will come along with an answer!

>> No.3007722

COSMOLOGISTS GET IN HERE AND ANSWER THIS GOD DAMN QUESTION.

>> No.3007800
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3007800

>>3007722
I don't know many cosmologists who actually do general relativity.

Anyway, if I understand you correctly, then you are searching for a path radially away from the back hole.
You're also considering light.
So take the Schwarzschildmetrik, set d\theta=0 and d\varphi=0 so you end up with a 2-dimesnional problem in r and t. then find the lightlike directions X:

g(X,X)=0

and plug it into the geodesic equations D_X(X)=0 so kill the remaining parameters.

You'll end up with some flow where you can choose start positions.

I will not do it for you but if you do, I'll comment on the calculation. You'll learn some GR while doing it, gogo

>> No.3007850

>>3007800
I'm too much of a noob to do this, I'm only starting undergrad mathematics in a few months.
;_;

>> No.3007917

Theoretically it stays on the event horizon, but in practice that would be like balancing a pencil on its tip.