[Hannah LS (OP)]

David asks:

If light cannot escape from a Black Hole, could one speculate that the gravitational pull from a Black Hole is faster than the speed of light?

What do you think?

[Colin2B]

David asks:

If light cannot escape from a Black Hole, could one speculate that the gravitational pull from a Black Hole is faster than the speed of light?

What do you think?

What reasoning are you using to reach that conclusion?

[Bogie_smiles]

David asks:


If light cannot escape from a Black Hole, could one speculate that the gravitational pull from a Black Hole is faster than the speed of light?


What do you think?

First of all, I'm not convinced that light cannot escape from a black hole. Gravitational attraction can bend light, and it seems possible that if enough mass is accumulated around a center of gravity, the gravitational attraction of the resulting massive object (black hole) could bend the path of light so severely that the light waves would curve back in toward the center of gravity of the black hole, making it appear that light cannot escape.


However, it is also possible that such a black hole is unstable and as its mass increases it becomes more and more unstable until it produces hot plasma jets and light from its poles, allowing light to escape that way.


Also, it seems possible that a black hole could accumulate matter and energy until a limit is reached, at which point it might collapse/bang into an expanding hot dense ball of energy, that then emits light in a massive burst of energy, and continues to produce photon energy from the expanding hot plasma.

Further, I see no reason why light waves and gravitational waves wouldn't traverse space at the same velocity, the speed of light and gravity being the same. Perhaps light waves and gravitational waves have some things in common, like they are both emissions, at the speed of light, from matter. The light waves would be emitted by photon particles, and the gravitational waves would be emitted by all objects with mass.


If that were true, then there would possibly be a corollary to that emissions scenario where photons and objects with mass absorb light and gravitational wave energy from the medium of space to replace the emitted wave energy.

[Janus]

David asks:

If light cannot escape from a Black Hole, could one speculate that the gravitational pull from a Black Hole is faster than the speed of light?

What do you think?

You are confusing two different things, a radiation ( such as light) with a field (gravity) responsible for an attraction.
There is also an electromagnetic field which is related to light(an electromagnetic radiation), and while the light radiation cannot escape the BH, the effects of the field can be felt outside of it.  Thus a BH can carry a charge which can be felt outside the event horizon.
In the same way there is both a field and radiation associated with gravity. Gravitational waves such as those detected by LIGO are the radiation (and cannot escape the BH event horizon),  However, it is the field that is responsible for what we feel as the gravitational force, and it remains after the BH forms.

[evan_au]

What is the 'speed of gravity'?

The most precise measurement of the "speed of gravity" was made for the merger of two neutron stars. The gamma ray burst was detected 1.7 seconds after the gravitational wave. 1.7s difference in a 130 million year journey is pretty close to a tie...

This is measuring the speed of disturbances in the gravitational field.

See; https://en.wikipedia.org/wiki/GW170817#Gamma_ray_detection

...the gravitational pull from a Black Hole is faster than the speed of light?

The gravitational field does not need to "escape" from the black hole, since the concentration of matter already deformed the gravitational field before the black hole formed.

There is another flaw with this theory: Even if the speed of gravity was twice the speed of light, that just means that there is another boundary at half the radius of the event horizon that gravity could not escape from - and all the matter is concentrated at the singularity within this inner sphere.

[chris]

A theoretical physicist once explained to me very clearly a lovely argument for why we believe gravity propagates at the speed of light; regrettably I cannot recall it!

Martin Rees was even more straightforward on the Naked Scientists when he joined us to discuss LIGO and gravitational wave experiments a few years back. He cited observed data, pointing out that the time differences between the detection of the waves at the different detector sites and the distance between those sites corresponded to a gravitational wave propagation velocity of c.

[yor_on]

Well, if we define lights speed in a vacuum as a field, to us 'propagating' measurable light signals (waves/photons), and then define gravity as another field (gravitons), then both are at 'c' to us. But as all paths (geodesics) possible for a light signal inside the event horizon only 'leads it back' there is no possibility to compare some sort of 'field strength/magnitude'. And as both must be at 'c', their 'speed' is equivalent.
=

Then again, maybe all is 'light/energy' inside that black hole?
But it doesn't matter for this, just as it doesn't matter how 'big' that black hole is etc.

Then again, again, if we just consider a field strength, then maybe it's possible to argue that the fact that light can't escape inside a event horizon must make a black holes 'magnitude' stronger than the 'light field' surrounding it.