Thursday, June 28, 2012

Transmission from InfiniG: in the ergosphere

My dear collaborators,

Let me tell you about my path toward Sgr A*. For the moment I'm feeling cheerful (and apologize for the gloom in the last few transmissions; I do of course appreciate this opportunity, and am finding joy in experiencing this amazing journey even though I miss you...)

Let's discuss spacetime. Let's think of it as a sheet of rubber pulled taut; and very massive objects, like planets, stars, black holes, etc, sit upon it and indent it. This, as you know, creates a structure for lighter objects to orbit heavier objects, and creates the foundation for what we call gravity. On earth you can see games for children in museums that use this structure: a very wide funnel in which you can roll a penny until it spirals to the center and falls into a hole. The penny spirals in due to friction; it loses energy with each "orbit". But in space, there would be no friction, and the penny could orbit on the same circular path without crashing in... the way our moon orbits the earth. Riding on this indentation in spacetime.

I have always enjoyed thinking of spacetime in this way.

When approaching a black hole like Sgr A* we encounter some complications in this structure. This black hole is rotating, and its rotation causes spacetime to warp. Inside a black hole's ERGOSPHERE, spacetime is dragged and stretched so much by the black hole's rotation that it is impossible for objects to be stationary with respect to a fixed point in the rest of the universe.

To illustrate this point, imagine a large lake covered with boats. You are in a rowboat in the middle of the lake, and you look far out to the edges of the lake and fix your eyes on a distant sailboat. To remain stationary with respect to that sailboat, all you need to do is stay right where you are. That might involve a little paddling here and there, but you can do it. Now imagine a spinning disk is placed in the center of the lake, and it causes a strong vortex at the surface of the water where you are. In your rowboat you simply cannot paddle such that you can remain stationary in relation to that faroff sailboat--the force of the vortex is too strong.

This metaphor of the lake is limited because we are thinking about boats on a 2-dimensional surface, and it is easy to imagine our little rowboat spiraling inward, inward, as if it is going down a drain. Let's now imagine objects moving in the universe in 3-dimensions. As they move around the black hole, their orbits will be skewed, and will resemble a tangled slinky due to warped, irregular spacetime.

You might enjoy this simulation:

   

Inside the ergosphere, objects do not necessarily careen into the black hole (and in fact, there is an interesting mode of escape called the Penrose Process, but that's for another time). If I wanted... I could stop here for a while and follow one of these magical tangled orbits...

Yours,
InfiniG

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