Black hole gravitational pull

[JuniorAlcala]

TL;DR Summary

Speaking about the gravitational pull of black holes

Do all black holes have the same gravitational pull yes or no, and if not, is it possible that if space and time bends on itself and connects two black holes that the one with the strongest pull will continue as a black hole and the weakest will turn into a white hole considering the amount of matter that is being pulled out by the stronger black hole? Theoretically speaking of course just a question seeking an answer of my curiosity .

 

[member 656954]

Do all black holes have the same gravitational pull

No they don't. Their gravity is dependent on their volume and density (and proximity of course).

As for connected BH's, nobody knows, though I'd think we'd have noticed if they were connected and the 'pulling' that you posit had a manifestation such as the less massive one shrinking in size (or perhaps even being dragged through space toward each other). If there is no manifestation in our space time (on the assumption that the connection is hidden behind the event horizon and therefore 'outside' our space time) then I doubt we'd ever know.

White holes are theoretical objects, and if we've seen any, we've not recognized them as such, but my (admittedly sketchy) understanding is that they don't form from black holes in any way - connected or otherwise - and if they do exist, we wouldn't expect to see them until the end of time.

But what I don't get in your question is why you think the less massive black hole would turn into a white hole? As long as there is an event horizon, they'll remain black, and it's not clear why a black hole of any kind should suddenly invert and start spewing matter.

 

[lomidrevo]

Their gravity is dependent on their volume and density

Neither volume nor density are well defined quantities for BHs. Mass, angular momentum and charge are the only relevant characteristics of a BH. The curvature of space-time around BH ("gravitational pull") depends only on these quantities.
https://en.m.wikipedia.org/wiki/Black_hole

 

[lomidrevo]

Summary: Speaking about the gravitational pull of black holes

Do all black holes have the same gravitational pull yes or no,

No, see my previous post. Mass of the black hole is the most significant quantity determining the gravitational field around it (as seen far from the BH).
The rest of your post seems to be a speculation, so I won't comment it as it is against the PF rules.

 

[member 656954]

Neither volume nor density are well defined quantities for BHs

Agree that BH mass is the ultimate measure of gravitational pull, but BH density is defined, being the mass divided by the volume within its Schwarzschild radius. On this basis, a SMBH could be less dense than water, which can lead to very gentle tidal forces (at least until you're well into the black hole) such as the event horizon of a 10M solar mass black hole having about the same tidal force between your head and feet as we do standing up on Earth.

That was my take on JuniorAlcala's question, and yes, the rest was speculation but so is string theory and quantum gravity, and they're discussed here, and sometimes even by laypeople

 

[Orodruin]

volume within its Schwarzschild radius

There is your problem. The ”volume within the Schwarzschild radius” is not a well defined concept due to how strongly space and time are intertwined there. Also note that the Schwarzschild radius is not in any way the distance from the singularity,

the rest was speculation but so is string theory and quantum gravity, and they're discussed here

The difference is that string theory, for better or worse, is actively discussed in the scientific community. What PF forbids is personal speculation and original research.

 

[member 656954]

No argument from me, there might have been a bulge in my cheek as I was typing

But it is an interesting point. When does "personal speculation" tip over into "actively discussed"? How much activity defines the measure?

If, as Biologist Danielle N. Lee said in an interview with Erica Anderson on Recode Decode recently, "...how science works, people are pursuing questions that are personally relevant", then everything discussed on PF is merely the consequence of answering personally interesting questions, and that has to start somewhere!

Anyway, that's the entirety of my speculation quota, I think, I'll settle down now.

 

[Orodruin]

When does "personal speculation" tip over into "actively discussed"? How much activity defines the measure?

According to PF rules, this occurs when the discussed matter is published in a reputable peer-reviewed journal in the relevant field. It is not a strict line, but it is a good guideline.

 

[lomidrevo]

how science works, people are pursuing questions that are personally relevant", then everything discussed on PF is merely the consequence of answering personally interesting questions, and that has to start somewhere!

The problem is that, once you allow discussion of personal theories and speculations, very soon it would be almost impossible (at least for non-professionals) to distinguish what is a verified fact and what is just nonsense.
I am sure you can find plenty of forums on Internet where you can discuss personal theories, philosophy and even speculations. But places like PF are quite rare (I think), and the rules helps to keep its mission:

Our mission is to provide a place for people (whether students, professional scientists, or others interested in science) to learn and discuss science as it is currently generally understood and practiced by the professional scientific community. As our name suggests, our main focus is on physics, but we also have forums for most other academic areas including engineering, chemistry, biology, social sciences, etc.

That is why I like it here!

 

[lomidrevo]

Agree that BH mass is the ultimate measure of gravitational pull, but BH density is defined, being the mass divided by the volume within its Schwarzschild radius.

This was already discussed on PF, you may want to read the below thread to further see why it is not very useful concept to define density and volume for a black hole:

https://www.physicsforums.com/threads/density-of-a-black-hole.870027/

 

[member 656954]

I am sure you can find plenty of forums on Internet where you can discuss personal theories, philosophy and even speculations.

Indeed you can, and I know that they can get pretty loopy, pretty quickly. The moderation of PF is definitely a plus with regards constructive, fact-driven discussions, even if newbies like myself sometimes wobble their way into full appreciation of the guidelines

 

[snorkack]

No.
We know what happens when a black hole is pulled by another black hole of similar size. We have seen 10 or so such events.
Nothing can be pulled out of a black hole by anything, including by another black hole. What happens when a black hole is pulled by another black hole is that the hole is pulled into another hole and stays whole while pulled into hole. They get slightly distorted and wobbling, but nothing gets out except gravity waves.

 

[Orodruin]

nothing gets out except gravity waves

What about gravitational waves?

 

[lomidrevo]

We know what happens when a black hole is pulled by another black hole of similar size. We have seen 10 or so such events.

Right, but based on the original post, I don't get the impression that OP is talking about black holes merging:

if space and time bends on itself and connects two black holes

So maybe some further clarification from OP about his thoughts would be required to elaborate any meaningful answer.

They get slightly distorted and wobbling, but nothing gets out except gravity waves.

To my knowledge, neither gravitational waves are originated "inside" the merging black holes (if this is what you suggest). The radiated energy comes from the decreasing orbital energy of the binary system as the black holes spiral in. So nothing really escapes the black hole (event horizon) during this process.

Btw. these are gravitational waves (as @Orodruin already hinted). Gravity waves are something totally different:
https://en.wikipedia.org/wiki/Gravity_wave

 

[PeterDonis]

is it possible that if space and time bends on itself and connects two black holes that the one with the strongest pull will continue as a black hole and the weakest will turn into a white hole considering the amount of matter that is being pulled out by the stronger black hole?

No.