4 ms·
This has curious similarity with errors which can appear in basic n-body simulations, where excessively close interactions can break orbits by throwing bodies t
by strainer 10y ago
This has curious similarity with errors which can appear in basic n-body simulations, where excessively close interactions can break orbits by throwing bodies too far from circumstances in one timestep to the next.
In n-body simulation the 'point gravity' objects are kind of mathematical singularities which never collide because they have no size. The integration time-step gives them a kind of radius or gradient of proximity where very large errors occur, where virtual energy can be added or lost.
I read in these cases of true black hole collision, the shedding of energy through gravitational waves is the main cause of their orbits decay - without making the waves, the holes could circle each other for a very long time. Presumably energy&momentum is maintained over the collision of the two astrophysical non-point singularities, unlike the basic n-body excessive gravitation phenomenon.
The full details of what actually happens during the collision/overlap of black-hole 'calculation radii' are surely mysterious.
- z3t4 10y agothis is also my experience with simulated gravity and galaxy systems. i guess newton physics alone would be enough to make a body flung out if it comes close enough. and i guess a merge is close enough. i was working on a space mmo and after leaving the server running for weeks some body would always be flyng away with crazy speed.
- strainer 10y agoThe newtonian model itself doesn't produce this behaviour as it is continuous, so however much bodies accelerate towards each other they can decelerate just as much once they have passed. In n-body simulation the continuous model is 'squeezed' into time-slices, where bodies can accelerate towards each other in one time-slice and in the next be too far past each other to slow each other down again. Seemingly in the real astrophysical world, blackholes will free-fall towards each other by their masses 'dragging' on spacetime, causing deep perturbations in spacetime (as gravity waves). Eventually there is a 'merge' as you called it, an operation during which the resulting merged body can get a directed kick from the persisting spacetime perturbations, one powerful enough to eject it from a galaxy. In the real world, overall it is expected energy and momentum is not defied during this merge operation, it seems remarkable considering how exceptional and energetic these events appear. edit ...on second thoughts, this 'merge event' produces GRAVITATIONAL PROPULSION - sorry for the caps but I think they might be justified.
- kristianp 10y agoFinally we have reactionless space travel! All we have to do is merge two black holes!
- AnimalMuppet 10y agoIt's not reactionless. It's essentially a "gravitational wave rocket".
- grigjd3 10y agoGeneral relativity is a continuous theory as well.
- abecedarius 10y agoIn Newtonian gravity you need at least three bodies to arrange an ejection: two of them start orbiting more tightly, to counterbalance the third one flying out to infinity. (IIRC this happens a lot in globular clusters, and simulations like yours.) With just two bodies you get only Newton's solutions, the conic sections.