Frame Dragging Direction for Outward Moving Test Mass

In summary: So, the correct answer is that the outward moving mass should be deflected in the opposite direction, relative to its velocity, as the inward moving mass.In summary, considering frame dragging, a test mass starting at rest or with an initial velocity pointing towards the center of a rotating mass will be deflected in the rotational direction. However, if the test mass starts near the rotating mass but is moving outwards with a velocity in the radial direction, the deflection will be in the opposite direction, relative to its velocity, as the inward moving mass. This is due to the fact that the "outward direction" is not the same for an observer close to the mass as for a distant Schwarzschild observer. This can be seen by looking
  • #1
Sonderval
234
11
I have the following question considering frame dragging:
A test mass starting at rest near a rotating mass or with an initial velocity pointing towards the center of the rotating mass will be deflected in such a way that it begins to move around the mass in the rotational direction. This is normal frame dragging.
Now consider the opposite situation: A test mass starts near the rotating mass but is moving outwards with a velocity in radial direction. In which direction would this mass be deflected?

According to standard formulations of gravitoelectromagnetism like here
http://www.arxiv.org/abs/gr-qc/0311030
the acceleration is proportional to v×B (with B being the analogue of the magnetic field); so if I reverse the velocity, the acceleration should be reversed as well, i.e., if a moving mass is deflected to the right relative to its velocity on falling in, a mass moving out should also be deflected to the right relative to its velocity.

But when I try to see this effect (for example using the program GRorbits
http://stuleja.org/grorbits/), the outwards moving mass is deflected in the co-rotating direction.

So I'm confused which answer is correct and where the mistake in my argument concerning the cross-product lies, if there is one.

I suspect that part of the problem may be that the "outward radial direction" depends on whether I look at the situation from the point of view of a distant Schwarzschild observer or a local frame, but I am not exactly sure how to see this more clearly or make this idea exact.
 
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  • #2
If I read (I'm using the word read rather loosely here, more like a momentary glance) the paper linked to correctly, ##B## should be along ##J##, the angular momentum of the mass. In this case the rotation of ##v## is about ##J## which means the change in ##v## would have the opposite sign if the direction is reversed.
 
  • #3
@Paul Arveson
Thanks. Yes, and this means that if a particle flying in one direction is accelerated to the right, a particle flying in the opposite direction is also accelerated to the right.
Actually, I think I found the problem: I looked only at the deflection of the orbit in GRorbits - but I should look at how the deflection changes over time. This shows that the direction of the acceleration is actually opposite to the rotation of the mass as the formula suggests.
The initial deflection of the orbit is due to the fact that the "outward direction" is not the same for an observer close to the mass as for a distant Schwarzschild observer.
 

1. What is frame dragging direction for outward moving test mass?

Frame dragging direction for outward moving test mass refers to the phenomenon in which a rotating massive object, such as a planet or star, causes the space around it to curve and drag nearby objects in the same direction as its rotation.

2. How does frame dragging affect the movement of objects in space?

Frame dragging can affect the movement of objects in space by changing their trajectory and causing them to move in a curved path instead of a straight line. This is due to the warping of space caused by the rotating mass.

3. What are the implications of frame dragging for space travel?

The implications of frame dragging for space travel are significant, as it can impact the trajectory and stability of spacecraft in orbit around massive objects. It can also affect the accuracy of navigation systems and the timing of spacecraft maneuvers.

4. How is frame dragging direction for outward moving test mass measured?

Frame dragging direction for outward moving test mass can be measured using various methods, such as using gyroscopes on spacecraft or analyzing the changes in the orbits of nearby objects. The Gravity Probe B mission was also specifically designed to measure frame dragging effects.

5. Can frame dragging direction be reversed or altered?

No, frame dragging direction cannot be reversed or altered. It is a natural consequence of the rotation of massive objects and is governed by the laws of physics. However, its effects can be counteracted or minimized through precise calculations and adjustments in spacecraft trajectories.

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