Tidal effects on event horizon of binary rotating BHs

[Christian Thom]

TL;DR Summary

The presence of a big mass in the vicinity of a BH must have an effect on the shape of the event horizon. When the system is rotating, it would lead to tidal effects on the horizon that would disclose internal material of the BH.

The presence of a big mass (BH or neutron star) in the vicinity of a BH must have an effect on the shape of the event horizon, an indentation comes logically to mind. When the system is rotating, it would lead to tidal effects on the horizon that would disclose internal material of the BH. This would even allow some of it to possibly escape to free space or to fall in the second massive body. This maybe would also, on the contrary, ease the capture of the content of an potential accretion disk. Or is these too Newtonian speculations ?

 

[PeterDonis]

internal material of the BH

There is no such thing. A BH is vacuum.

Or is these too Newtonian speculations ?

Basically, yes. A black hole is not an ordinary object, and the horizon is not an ordinary surface.

There are no known exact solutions for a massive object near a BH, either orbiting or falling in, so cases like this have to be studied numerically. However, heuristically I think the following is a reasonable description:

(1) If the massive object is orbiting, it has to be orbiting far enough from the hole that effects on the hole's horizon are negligible.

(2) If the massive object is falling in, the horizon grows, it doesn't shrink, so any intuitions based on the massive object "pulling" against the pull of the hole obviously don't apply.

 

[Christian Thom]

Thank you for your reply.
I nevertheless would not be so positive about the vacuity of the BH. It is true that the Schwarzchild are only valid for vacuum space, but that doesn't mean that the actual BH are of this kind.
As for the tidal waves, we have a some evidence for them : gravitational waves that have been detected during fusion events.

 

[Vanadium 50]

I am having a hard time distinguishing your response from "I am not going to do the calculation myself, but I think you're just wrong" or possibly "maybe GR is just wrong in some unspecified way".

If this isn't where you are coming from, it would be helpful if you would clarify. Ideally with calculations.

 

[PeterDonis]

I nevertheless would not be so positive about the vacuity of the BH.

You should be. While it is true that actual BHs are formed by the collapse of massive objects, so there will be a portion of the spacetime inside the horizon that is not vacuum, it is clear both from exact solutions like the Oppenheimer-Snyder model and numerical simulations that the non-vacuum portion of the interior plays no significant role once the hole is formed. So treating actual BHs as vacuum is still the best model.

It is true that the Schwarzchild are only valid for vacuum space, but that doesn't mean that the actual BH are of this kind.

As far as anything we can detect from the outside is concerned, actual BH will be described, except for the portion of the spacetime occupied by the collapsing matter (which, as above, plays no significant role once the hole is formed) by a solution in the Kerr-Newman family of solutions, which are vacuum. This has been a known theorem since, IIRC, the late 1960s.

As for the tidal waves, we have a some evidence for them : gravitational waves that have been detected during fusion events.

We have detected gravitational waves from mergers, yes. But these are nothing like what you describe in your OP.

 

[Ibix]

but that doesn't mean that the actual BH are of this kind.

Semi-realistic models of stellar collapse such as Oppenheimer-Snyder have an interior that is mostly vacuum. There are no models I'm aware of where there's matter hanging around just inside the event horizon, anyway. Certainly not in vanilla GR.

As for the tidal waves, we have a some evidence for them : gravitational waves that have been detected during fusion events.

Yes, and they match GR predictions to the best precision available - so we are talking of event horizons that reach towards each other and cannot reveal anything that's crossed them.

 

[Christian Thom]

Thank you all. I surrender !