The mass of a super massive Black Hole measured in Suns.

Rhys Essien

Holy Moly.

http://i.imgur.com/MUg63B0.gifv

Triangla

It would be cool if they showed how much volume the super massive black hole took up.

Mind blowing mass!

sbsquarepants

Wow.

Am I wrong in thinking the volume is the same regardless of the mass? ie a single (non dimensional???) point?

Triangla

sbsquarepants wrote: »

Wow.

Am I wrong in thinking the volume is the same regardless of the mass? ie a single (non dimensional???) point?

Mass is the the amount of matter in an object. Measured in kilograms. Volume is the space it takes up.

For example a litre of water being 1kg. A litre of a different material might be 10kg or 0.50kg.

riffmongous

Triangla wrote: »

Mass is the the amount of matter in an object. Measured in kilograms. Volume is the space it takes up.

For example a litre of water being 1kg. A litre of a different material might be 10kg or 0.50kg.

No I think he's right in a way, a black hole is a singularity isn't it? an infinitely small volume. The size of the event horizon will change with mass

but sure didnt all the mass/energy in the entire universe come from a singularity in the first place?

Popoutman

The dimensions of a black hole are generally regarded as the mass, the radius of the event horizon (that point at which light can no longer climb out of the gravity well). The event horizon size, gives the volume and is directly related to the mass and doesn't generally need to be expressed separately as the relationship does not differ between black holes.

Depending on which set of theoretical physics you follow, there may also possibly be an electric charge and a physical spin of the black hole. Either way, the amount of things you need to know to completely define a black hole is very small.

sbsquarepants

Triangla wrote: »

Mass is the the amount of matter in an object. Measured in kilograms. Volume is the space it takes up.

For example a litre of water being 1kg. A litre of a different material might be 10kg or 0.50kg.

I know that - what I mean is if you increase the mass of a singularity does it's volume increase? Or are all singularities of equal volume regardless of mass?

If something is infinitely dense and infinitely small and you double the amount of stuff in it - it's still infinitely dense and infinitely small (but supposedly a different sized infinity?)
I have no idea if that translates to an actual physical difference in volume though to match the physical difference in mass. I can't see why it wouldn't, but I also can't see how it could!:) Surely a point, is a point, is a point or is that the wrong way to look at it?

Carawaystick

Popoutman wrote: »

Depending on which set of theoretical physics you follow, there may also possibly be an electric charge and a physical spin of the black hole. Either way, the amount of things you need to know to completely define a black hole is very small.

What set of physics would not have conservation of angular momentum?

It is highly unlikely that a black hole would not be rotating, same as the liklihood of a star not rotating

Chemical Byrne

riffmongous wrote: »

No I think he's right in a way, a black hole is a singularity isn't it? an infinitely small volume. The size of the event horizon will change with mass

but sure didnt all the mass/energy in the entire universe come from a singularity in the first place?

I think what he's getting at is what volume would it look like if it were the same density as, say, the earth or sun maybe?

sbsquarepants

Popoutman wrote: »

The dimensions of a black hole are generally regarded as the mass, the radius of the event horizon (that point at which light can no longer climb out of the gravity well). The event horizon size, gives the volume and is directly related to the mass and doesn't generally need to be expressed separately as the relationship does not differ between black holes.

.

This is kind of what I'm getting at. You begin with a black hole of a given mass - you feed it with material until it's mass has doubled - the event horizon extends by some proportional amount (I'm unsure what the exact formula is, but it's proportional somehow) - but what happens to the actual physical space that the now doubled mass occupies - does that change or does it not, or do we know.
Maybe I shouldn't be thinking in terms of volume at all, only of event horizon?

greedygoblin

sbsquarepants wrote: »

This is kind of what I'm getting at. You begin with a black hole of a given mass - you feed it with material until it's mass has doubled - the event horizon extends by some proportional amount (I'm unsure what the exact formula is, but it's proportional somehow) - but what happens to the actual physical space that the now doubled mass occupies - does that change or does it not, or do we know.
Maybe I shouldn't be thinking in terms of volume at all, only of event horizon?

The Schwarzchild radius isn't it that measures the radius of the event horizon:

[latex]r = \frac{2Gm}{c^2}[/latex]

So I suppose you could measure the volume of the space contained within the event horizon assuming a perfectly spherical black hole?

sbsquarepants

But the space contained within the event horizon is merely a measure of the distance from the centre to where the gravity weakens to the level where light can escape. My question is does the actual physical volume of the mass creating that gravity change or does it remain the same.

Myrddin

sbsquarepants wrote: »

My question is does the actual physical volume of the mass creating that gravity change or does it remain the same.

As in the singularity itself, does it occupy a larger amount of space as it's mass grows?

greedygoblin

But isn't the singularity more or less a mathematical construct? The equations describing the black hole effectively say that at this point at the centre of the black hole the force of gravity is infinite. Physics as we know it breaks down.

sbsquarepants

Myrddin wrote: »

As in the singularity itself, does it occupy a larger amount of space as it's mass grows?

Exactly.

A singularity (to my mind) is a single point. Are they a one size fits all phenomenon?

I know the mass of any individual black hole and consequently it's gravitational pull and event horizon can be greater or lesser than another. But the actual volume of the singularity - is that the same in all cases?

mickmackey1

sbsquarepants wrote: »

But the actual volume of the singularity - is that the same in all cases?

The idea of measuring the volume of a singularity doesn't really make sense - a singularity is defined as having zero volume and infinite density, so if it did have a measurable volume, it would no longer be a singularity.

As mentioned above, the laws of physics break down in these extreme situations, and the laws of language tend to break down also. We are forever doomed to endless circular waffling

Rhys Essien

Two black holes merging.

http://i.imgur.com/AOCqg5j.gifv

Myrddin

I know it's all theoretical & there's no known answers yet, but to say that a singularity has infinite mass - is that just another way of saying it has enough mass to generate gravity strong enough to require faster than light speed to escape, & it sufficiently breaks our mathematical models? Surely the singularity is still a physical object of incredible mass and density, & some are 'bigger' than others no?

Zubeneschamali

Myrddin wrote: »

to say that a singularity has infinite mass

It doesn't have infinite mass, it has some definite amount of mass, like 3 times the mass of the Sun.

It has infinite density, because all that mass is at a single geometrical point in space, with no dimensions.

But when people talk about the size of a black hole, they usually mean the size of the volume surrounded by the event horizon.

sbsquarepants

mickmackey1 wrote: »

The idea of measuring the volume of a singularity doesn't really make sense - a singularity is defined as having zero volume and infinite density, so if it did have a measurable volume, it would no longer be a singularity.

As mentioned above, the laws of physics break down in these extreme situations, and the laws of language tend to break down also. We are forever doomed to endless circular waffling

Not zero volume surely. Infinitely small volume - but still an actual physical volume nonetheless?

Maximus Alexander

sbsquarepants wrote: »

Exactly.

A singularity (to my mind) is a single point. Are they a one size fits all phenomenon?

I know the mass of any individual black hole and consequently it's gravitational pull and event horizon can be greater or lesser than another. But the actual volume of the singularity - is that the same in all cases?

Mathematically a singularity always has 0 volume and infinite density.

If you want to talk about the 'size' of a black hole then you would be talking about the mass or Schwarzschild radius. They are both proportional to one another.

Ace Attorney

So would it be right to say the singularity doesnt change size, no matter the different size of each blackhole, the added mass is added to the event horizon and the singularity just swallows everything. Like the singularity is the mouth and the event horizon is like a body that puts on weight.

mickmackey1

sbsquarepants wrote: »

Not zero volume surely. Infinitely small volume - but still an actual physical volume nonetheless?

If an infinitely small volume is possible, so is zero volume - the mathematical probability is the same.

endacl

So.....

What's that in old money?

sbsquarepants

mickmackey1 wrote: »

If an infinitely small volume is possible, so is zero volume - the mathematical probability is the same.

I always have trouble wrapping my head around these kind of concepts - to my mind infinitely small has to be bigger than zero. Zero is nothing, infinitely small is something, no?

It's like the thing of 0.99 recurring equalling 1.
I know it does - but I just can't see how it does!

Maximus Alexander

sbsquarepants wrote: »

I always have trouble wrapping my head around these kind of concepts - to my mind infinitely small has to be bigger than zero. Zero is nothing, infinitely small is something, no?

It's like the thing of 0.99 recurring equalling 1.
I know it does - but I just can't see how it does!

Because there is no number between 0.99 recurring and 1, so they have to be equal.

Any two distinct numbers will have an infinite number of real numbers between them.

sbsquarepants

Cheers maximus!

As I said, - logically, I know that to be the case, but I just can't seem to shake the feeling that it "should" be just a tiny bit less!
If you know what I mean:D

Maximus Alexander

sbsquarepants wrote: »

Cheers maximus!

As I said, - logically, I know that to be the case, but I just can't seem to shake the feeling that it "should" be just a tiny bit less!
If you know what I mean:D

I know exactly what you mean

ps200306

A singularity isn't a "thing". I think the term has been bandied around about black holes for so long that people imagine the singularity is some strange physical entity that lives at the centre of the hole. In fact, a singularity is the purely mathematical term for the point at which a function takes an infinite value. Here's a simple one:



The step function (or rather, its derivative) contains a singularity because its slope is infinite at the step.

The black hole singularity is a physical impossibility as far as we know. Scientists hold out hope that it will somehow be sidestepped by physics that we don't yet understand, and that in reality there is no singularity. In the meantime we are saved from having to worry about it by the cosmic censorship hypothesis and the lack of naked singularities. From outside the event horizon we can never see anything inside.

If we treat the black hole volume as the volume inside the event horizon then we can work it out for the 20 billion solar mass hole in the OP. (Actually a rotating black hole has two event horizons, with maximum separation at the equator and coincident at the poles, with a region in between called the ergosphere; don't ask me what happens there ).

For a non-rotating black hole, we get:



That's a radius of about 400 times the distance from the earth to the sun, or more than ten times the distance from the sun to Pluto, or about two and a quarter light days. You can work out a volume, but it's silly money, nearly 10³³ cubic kilometres.

Also see this very excellent previous thread.

Myrddin

Fascinating stuff. Though I have to admit, I have to try & understand all of this without the aid of mathematics For me, it has to be all visual, so I have a hard time trying not to picture anything at the centre of a black hole...I just feel something has to be creating that enormous gravity well, and something can't be nothing

ps200306

Myrddin wrote: »

Fascinating stuff. Though I have to admit, I have to try & understand all of this without the aid of mathematics For me, it has to be all visual, so I have a hard time trying not to picture anything at the centre of a black hole...I just feel something has to be creating that enormous gravity well, and something can't be nothing

If it's any help, one of the conceptual difficulties is the idea that the black hole volume is an ordinary three-dimensional volume, with stuff "inside it". It's not like that. One of the posters on that other thread I linked gave a good explanation of why not, although it was a bit mathematical. You have to remember that gravity does not just warp space, but the space-time manifold. If you've seen the rubber sheet analogy, where the black hole sinks down into a depression on the rubber sheet, it is not just deforming a third space dimension. The two-dimensional surface of the sheet is supposed to represent all three spatial dimensions.

The black hole's gravity warps space and time, in a sense mixing them into each other. This is not unique to black holes -- the effect is just most extreme there. Even here on earth, the warping of space-time by the earth causes clocks to run slower on the surface of the earth than on, say, an aeroplane or the space station. This has been experimentally measured beyond a shadow of a doubt, and has to be allowed for in the GPS system for example.

Inside the black hole's event horizon, there is no spatial direction corresponding to "outward". Crossing the event horizon is a one-way ticket. You can perhaps visualise this in terms of light cones, a traditional mechanism for describing the possible paths (or "world lines") of objects in space-time. The path taken by light is along the edge of the light cone. In General Relativity this path is referred to as a null geodesic. At the event horizon of a black hole the light cones flip over, so that the null geodesics all follow paths inside the horizon (in these pictures, "inside" means to the left of the event horizon line):





It is sometimes described by saying that inside the event horizon all possible futures lead to the singularity. Once inside, you can have a past outside the horizon, but not a future. In this sense, the event horizon divides the universe into two parts, with only one-way communication between them.

Another weird consequence of the warping of time at the event horizon is that for any observer outside it, any object passing through the event horizon will appear to freeze since time will come to a halt (only as measured by the observer outside ... for the falling object things proceed as normal). This gives another dichotomy between us observers outside and anything inside -- everything inside is infinitely far in our future. So in that sense we don't have to worry about singularities: as far as our part of the universe is concerned they never form within the lifetime of the universe as measured by our own clocks.