How Can Black Holes Vary in Size if They Are Singularities?

[kickaxe]

TL;DR

How are blackholes the same

I may be missing something.

A black hole is supposedly a 'sinkhole' in spacetime.It is a singularity, where a star collapses into a single point in space.

My question is about so called massive black holes.

If a black hole is a singularity, meaning it essentially has has no real size, being just a single point, how could one be larger than another?

Probably answered before, but I am new here.

And saying it accrues matter, etc. makes no sense. A point cannot accrue anything, otherwise it wouldn't be a point any longer, hence couldn't be a black hole.

 

[PeroK]

If a black hole is a singularity, meaning it essentially has has no real size, being just a single point

It isn't. A Black Hole is an extended spacetime geometry. It includes an event horizon and a central singularity. Note that the singularity is not a point in space, but a breakdown of the mathematical model - which means that, technically, what happens at the singularity is outside our current knowledge.

 

[weirdoguy]

Note that the singularity is not a point in space, but a breakdown of the mathematical model

And if you want to think about it as a point (that is not part of the spacetime, since maths break down there) it's more of a moment in time than place in space.

 

[kickaxe]

I know it has an event horizon. But a singularity is a singularity. A single point in 'space time' according to math or 'reality'. So how does one or the other have an extended have more inflluence over another?

 

[PeroK]

I know it has an event horizon. But a singularity is a singularity. A single point in 'space time' according to math or 'reality'. So how does one or the other have an extended have more inflluence over another?

A black hole has three characteristics: mass, charge and angular momentum. It's not a point in space.

 

[weirdoguy]

But a singularity is a singularity

And is not a black hole, nor is a part of spacetime, as been said. The premise of your question is wrong, so you must rethink your questions having that in mind.

 

[Bandersnatch]

I think it's best to think of black holes outside in, rather than inside out. I.e. don't start with the singularity.

You have a thing that is just like any other thing in space - there's some mass that has gravity, and the more compressed the mass, the higher the gravity it can reach as you get closer - only in the case of BHs, there's enough mass in small enough a region to create the event horizon. Without even getting into what goes inside, beyond the horizon, it remains true that if you put more mass in the object, it'll have even more gravity, which translates to the horizon being further out.
That's the black hole - it's this mass surrounded by the event horizon. The more mass it has, the larger the horizon.

Now, if you were to try and figure out what could possibly be going on beyond the horizon, using all the currently understood physics, you would conclude that there is no physical process that could stop the mass inside from compressing until it has zero size. That's the singularity.
Does it make physical sense for all the mass to be compressed to zero size? - maybe? possibly not? But you can still use your physics toolkit to try and describe in a self-consistent manner what the interior would look like, in terms of fields and geometry and causal interactions, with all the mass in the singularity and otherwise empty. Once you assume that there can be a mass in the form of a singularity, then it shouldn't matter to you whether that mass is X or 2X or X+1 or any other amount.

And in any case, whether that interior description is physical (i.e. corresponding to reality) or not, it doesn't change the properties you see outside the event horizon - that the black hole behaves like any other mass creating its gravitational field that depends on how much mass in how small a region there is.

 

[kickaxe]

Ok, a black hole is a singularity in space time (or a moment) where gravity is infinifte at that point. That's basically the definition of a BH. I know event horizon. You are misdunderstanding my question.

How can one bh be 'bigger' than another?

One infinite in space should be just as infinite as the other.

There are black holes and 'super' black holes. What's the difference?

 

[Bandersnatch]

Ok, a black hole is a singularity in space time

It isn't. A black hole is a mass surrounded by the event horizon. That may or may not have a singularity in it.

 

[kickaxe]

An event horizon is when nothing can escape the gravitational pull. So what does that except a singularity?

Still doesn't answer my question.

 

[phinds]

An event horizon is when nothing can escape the gravitational pull. So what does that except a singularity?

Still doesn't answer my question.

Because you have a belief that "singularity" denotes something physical but it does not (except in nonsensical pop-sci presentations). It simply indicates a place where our math model "breaks down" in the sense that it gives us a infinite answer and thus is not considered a physical reality.

 

[weirdoguy]

Ok, a black hole is a singularity

You had 5 (five!) answers saying that black hole is NOT a singularity, and your response is this?

Still doesn't answer my question

Your question is based on a false premise. Rephrase your question without thinking about singularity.

 

[kickaxe]

I understand that a singularity is a mathematical 'construct'. I was speaking either 'real' or 'theoretical' , So many quotes. Lol. If anyone could read what what I originally asked, what is the difference between a bh and a super massive bh. Stop being pedantic please.

I just wanted to know how a real or theoretical, can be larger or more powerful than another when they are all mathematically or otherwise singularities. Though you all seem to hate that term for some reason.

 

[phinds]

what is the difference between a bh and a super massive bh

amount of mass

 

[phinds]

I just wanted to know how a real or theoretical, can be larger or more powerful than another when they are all mathematically or otherwise singularities.

Since they are not singularities, your question continues to be based on a false premise. If you would get the fundamentals right, you could answer your own question.

You are beginning to sound like a troll, just saying over and over that black holes are singularities when you have been told repeatedly that they are not.

 

[weirdoguy]

when they are all mathematically or otherwise singularities.

Now you have 8 posts that says that black holes are not singularities, and you write that they are. Are you here to learn?

 

[Bandersnatch]

Cough. This is a conversation, people. Both sides are supposed to try and get into each other's headspace for communication to take place.

I just wanted to know how a real or theoretical, can be larger or more powerful than another when they are all mathematically or otherwise singularities. Though you all seem to hate that term for some reason.

It's good to clarify the terminology before zeroing-in on the issue, so that we all know we're talking about the same thing. The point of the comments above was to stress that the black holes are much more about the event horizons, than they are about gravitational singularities. The latter are almost incidental.

But let's talk about those.
The strength of a gravitational field depends on two things: mass, and distance from that mass. When one talks about a singularity, one talks about the second thing being reduced to zero. At which point you're dividing by zero and the whole thing stops making sense (that's almost literally what a singularity is in the mathematical sense).
But before you get to zero, the strength of the field approaches infinity. The closer, but not quite there, you get, the smaller a number you're dividing by.
Still, for any - arbitrarily close to zero - distance, the first of the two things listed earlier, the mass, can still vary between black holes.
You could, for example, imagine two BHs, one more massive than the other. You could then pick a distance - any distance - from its centre*, whether outside or inside its event horizon, and measure the strength of the gravitational field. It would be stronger for the more massive one, since you're multiplying by a larger number.
You could pick any number of pairs of distances and compare those, finding out that while for both holes gravity approaches infinity as you get closer to the centre, it does so faster for the more massive one. All because there is more mass contained in that central point. At the central point it's infinity for both, but it's how fast you get to that infinity what defines how the black hole looks from the outside.

*we're cheating here a bit by thinking purely in Newtonian terms, but I'm hoping relativitists (relativists?) will forgive us.

 

[kickaxe]

Still noone answering me. Sorry 'singularity' is a trigger word.

If all blackholes have infinite mass, how is one more massive than another?

Event horizons, I understand, but again, if they are all infinitely massive with infinite gravity, how can they have different event horizons?

Explain please

 

[Ibix]

If all blackholes have infinite mass

They don't.

they are all infinitely massive

They aren't.

with infinite gravity

You'd have to define what you mean by infinite gravity.

Explain please

You seem to have a lot of misconceptions about black holes. Are you going to listen to comments describing them correctly?

 

[russ_watters]

Ok, a black hole is a singularity in space time (or a moment) where gravity is infinifte at that point. That's basically the definition of a BH. I know event horizon. You are misdunderstanding my question.

How can one bh be 'bigger' than another?

It just seems like you aren't listening. When people colloqually talk about the "size" of anything they may be referring to its physical dimensions or its weight/mass. So when people talk about the "size" of a black hole, they are referring to either the mass or radius of the event horizon.

Or, from the other direction: yes, all black hole singularity are the same and they don't contain any information about the "size" of the black hole(beyond just being a broken equation, which is why physicists believe they don't exist). So, again, that's not what people are referring to when they describe a black holes size.

One infinite in space should be just as infinite as the other.

That isn't true either, but that's a different issue...

There are black holes and 'super' black holes. What's the difference?

As said: mass and therefore event horizon radius.

 

[PeterDonis]

If a black hole is a singularity, meaning it essentially has has no real size, being just a single point

It isn't. As you have been told, a black hole is an extended spacetime geometry. To the extent it has a "size", its size is the area of its event horizon.

Even the singularity itself is not a point. It's a spacelike line, i.e., a moment in time that is to the future of every event inside the horizon.

If all blackholes have infinite mass

They don't. Every black hole has a finite mass.

You have been given these answers, and they are correct. Further discussion is pointless if you're not going to listen to them. Thread closed.