Question Oi! Cadelin!

[Scouse]

So. Black holes and their formation. I got me a few questions.

Below 20 solar masses a star collapses into a neutron star, yup?

Between 20 and 40/50 solar masses you get a big fuck off supernova, right?

Above 40/50 solar masses it just collapses? No supernova? I'm presuming gravity is too much for the external shell of the star to be repulsed outwards?


I'm roughly with teh above. The question I'm most interested in is:

What would happen if you had a big fuck off mass (not a star, just a large amount of matter) - say a hundred billion* stellar masses?





*don't worry that a large amount of matter like that doesn't exist. What would happen if it popped into existence?

 

[Chilly]

Like a galaxy? You'd end up with the thing that's at the centre of many galaxies - a super massive blackhole.

 

[Scouse]

Nah. There's vast astrononical distances between the stars. I mean a big fuck off block of matter

 

[Krazeh]

I think the theory is you'd get a hypernova where everything collapses straight to a black hole but then jets out two fuck off huge streams of plasma from the poles. But I could be wrong.

 

[DaGaffer]

I was under the impression that about 200 solar masses was about the upper limit for any object? Beyond that size they can't shed energy fast enough to remain stable so they eject mass until they get to stability? Something like that.

 

[Scouse]

If it's just a big lump of carbon?

Either way. If it appeared, by magic

 

[DaGaffer]

If it's just a big lump of carbon?

Either way. If it appeared, by magic

Even if it appeared by magic. It would spin apart into smaller masses.

 

[Scouse]

Why?

Surely all the constituent parts would simply er, gravitate, towards the centre of gravity?

I didn't say big spinning mass. I said large chunk of stuff

 

[Chilly]

gravitate, pick up the tiniest fraction of angular momentum, increase temperature by 1000000 orders of magnitude due to compression and then end up spinning and exploding like a motherfucker.

 

[Scouse]

Surely it's more likely that it would split and several black holes would form? The centre would obviously be a black hole, but given the mass surely it's not the only place that would have sufficient density to form a singularity?

I'm more of a matter gets sucked in rather than it explodes kinda guy.

 

[DaGaffer]

Surely it's more likely that it would split and several black holes would form? The centre would obviously be a black hole, but given the mass surely it's not the only place that would have sufficient density to form a singularity?

I'm more of a matter gets sucked in rather than it explodes kinda guy.

No because you said it was all carbon, which means uniform density. Black Holes don't form simply because of an excess of mass; they have to collapse, but why would a homogeneous object collapse? You need heterogeneity to make it happen.

 

[Scouse]

A hundred-billion stellar mass object would collapse because of it's mass. Gravity would draw it all in towards the centre, just as usual.

If a 50+ stellar mass object is supposed to collapse without the supernova. Just jets of gamma rays out at either end. I suspect that a hundred-billion stellar mass object would collapse into several black holes that would then attract each other through their own gravity.

I wonder what it looks like when black holes merge? I presume they just add their masses to each other...

 

[Wij]

A big lump of carbon pulled to hyper density by gravity would start the carbon fusion cycle. If it was above the mass of normal main sequence stars it would eject mass due to excess energy. The type of mass you're talking about though is silly for just popping into existence. Would it start at uniform density?? What density would it be?

 

[Scouse]

[this] is silly ...

Yes. It is. But anyway....

....how about a large lump of beef? One the mass of a hundred billion stars?


Why does it get to eject mass if stars over 50 sun-masses just collapse and wang out jets of gamma radiation? Last I heard 100,000,000,000 was definitely over 50?

A 40-sun mass rump would start the fusion cycle. Why would an even bigger steak revert to the 20-50 sun-mass model of black hole formation when a 100-sun mass fillet would suck itself up sans explosion and jet out gamma...?

And as for my other question - surely multiple black holes would form, then coalece? What happens when two hit?


Where's the proper physicist when you need him? You'd have thought a thread shouting him over would actually get him interested!

 

[Wij]

Why does it get to eject mass if stars over 50 sun-masses just collapse and wang out jets of gamma radiation? Last I heard 100,000,000,000 was definitely over 50?

haven't read the rest yet but you seem to be missing the point that stars that collapse to black holes do so because they have used up all their fuel. Carbon is a great fuel under pressure though. Beef I'd need to think about.

 

[Scouse]

So, if you add beef to a star, you just increase the size of the star?

Cool

Edit: I still think a large enough mass popped into existence it would have such an epic amount of gravity at it's centre that the formation of a singularity would happen immediately - regardless of the density of the material there.

If it was a big cubed chunk of beef I reckon the middle of it would get black-holed straight away, two big jets of gamma radiation would fry their way out at the top and the bottom and the rest would start falling into the event horizon...

 

[DaGaffer]

Yes. It is. But anyway....

....how about a large lump of beef? One the mass of a hundred billion stars?


Why does it get to eject mass if stars over 50 sun-masses just collapse and wang out jets of gamma radiation? Last I heard 100,000,000,000 was definitely over 50?

A 40-sun mass rump would start the fusion cycle. Why would an even bigger steak revert to the 20-50 sun-mass model of black hole formation when a 100-sun mass fillet would suck itself up sans explosion and jet out gamma...?

And as for my other question - surely multiple black holes would form, then coalece? What happens when two hit?


Where's the proper physicist when you need him? You'd have thought a thread shouting him over would actually get him interested!

I don't think you can answer the question because there isn't a way in physics for such a large object to form; everything in the universe accretes due to gravity and layers into denser and denser objects, and that's also what gives you the upper mass limit because objects are formed from "the inside, out" if you will. Trying to work out what happens to a massive object that just pops into existence doesn't feature in the maths. I would imagine it would be an "it depends" answer; e.g. how fast does the "beef" (hydrogen, oxygen and carbon essentially) collapse? does the object have time to eject matter into smaller masses (no maths available) or does it just collapse down as a block (also no maths available).

NB, if your question is really just about what happens when black holes merge, then there is plenty of maths for that and it must have happened in the early universe, and the answer seems to be "there are several potential outcomes". Its almost impossible now because objects of sufficient mass are too far apart.

 

[Scouse]

I don't think you can answer the question because there isn't a way in physics for such a large object to form

I disagree. Regardless of the physics leading up to the event, the physics after the event should proceed as usual.

Physics should be able to predict what would happen to impossible objects...

everything in the universe accretes due to gravity and layers into denser and denser objects, and that's also what gives you the upper mass limit because objects are formed from "the inside, out" if you will

Yep. As I said above - surely in this case a supermassive fillet steak would pop into existence with more than enough gravity for the centre of it to immediately collapse into a singularity. The beef surrounding that would then get sucked in?

Trying to work out what happens to a massive object that just pops into existence doesn't feature in the maths.

.

So, basically, what you're saying is that I've come up with a question that would be fun for undergraduate physics students to work on?

 

[Raven]

God did it.

 

[DaGaffer]

I disagree. Regardless of the physics leading up to the event, the physics after the event should proceed as usual.

Physics should be able to predict what would happen to impossible objects...

Nooo, because there isn't an "as usual" scenario for the physics to proceed from.

Yep. As I said above - surely in this case a supermassive fillet steak would pop into existence with more than enough gravity for the centre of it to immediately collapse into a singularity. The beef surrounding that would then get sucked in?

No, this is what I mean about there being no maths. When an object collapses into a black hole its not instant; and in your example there would a bunch of intermediate steps before the black hole; fusion would have to start, burn through its fuel etc before initiating the collapse, and in your case you'd have a situation where that was going on while all this extra mass, way beyond the upper limit of a natural star, is acting on the core, which can't happen in nature because a natural object wouldn't get that big before breaking up.

So, basically, what you're saying is that I've come up with a question that would be fun for undergraduate physics students to work on?

No I think you've come up with a question that's a waste of time.

 

[Tuthmes]

So. Black holes and their formation. I got me a few questions.

Below 20 solar masses a star collapses into a neutron star, yup?

Between 20 and 40/50 solar masses you get a big fuck off supernova, right?

Above 40/50 solar masses it just collapses? No supernova? I'm presuming gravity is too much for the external shell of the star to be repulsed outwards?


I'm roughly with teh above. The question I'm most interested in is:

What would happen if you had a big fuck off mass (not a star, just a large amount of matter) - say a hundred billion* stellar masses?





*don't worry that a large amount of matter like that doesn't exist. What would happen if it popped into existence?

They do exist. Also you forgot quark stars, which should be in between the neutron and the black hole.

Hypernova.

http://en.wikipedia.org/wiki/Hypernova

VY Canis Majoris (1800–2100 solar radii).

http://en.wikipedia.org/wiki/VY_Canis_Majoris

Wolf-Rayet star.

http://en.wikipedia.org/wiki/Wolf–Rayet_star

Supermassive black hole.

http://en.wikipedia.org/wiki/Supermassive_black_hole

First, the average density of a supermassive black hole (defined as the mass of the black hole divided by the volume within its Schwarzschild radius) can be equal to (for 1.81×108 solar mass black holes) or less than (for >1.81×108 solar mass black holes) the density of water.

Also, the tidal forces in the vicinity of the event horizon are significantly weaker. Since the central singularity is so far away from the horizon, a hypothetical astronaut traveling towards the black hole center would not experience significant tidal force until very deep into the black hole.

 

[Zede]

and stars like this, which by all accounts was the biggest star ever and cannot be explained..

http://digitaljournal.com/article/310981

 

[Scouse]

fusion would have to start, burn through its fuel etc before initiating the collapse

Why would fusion "have" to start?

If there was that much mass then gravity would already be at the required level. In this instance it matters not one jot that fuel hasn't burned away - the condition required to cause a singularity to form - i.e. an epic amount of gravity - has been met by the existance of such a massive object.

Remember, it's gravity that forms the singularity...

Nooo, because there isn't an "as usual" scenario for the physics to proceed from.

I still say "rubbish". You don't need an "as usual" scenario where the maths is already worked out - you'd have to work it out. I can see no barrier (other than the fact that the mass would have to appear in the first place) to us working out such a problem.

I think you're just miffed that it's a little silly

 

[Wij]

Remember, it's gravity that forms the singularity...

And it's fusion energy release that forces it all apart.

 

[Scouse]

And it's fusion energy release that forces it all apart.

Don't disagree with that. But considering a large lump of beef isn't currently undergoing fusion when it pops into existence with enough gravity to form a singularity then the singularity will get formed straight away. It's not going to "wait" until fusion's started - a black hole is going to form wherever the gravity is high enough.

Fusion would start outside of that - but because of the mass of the black hole (100 billion suns worth of mass) then you're going to have a heck of a gravity gradient...

 

[Tuthmes]

Something (matter) doesnt just pop into existence though.

Secondly it is fusion that stops the core from collapsing. When it's burned up, then (if it has a large enough mass) it will collapse in on itself. So even if you pop something into existance that is large enough to form a black hole, you need to know what it is made of.

 

[Scouse]

Beef, thumes. Read the fucking thread

 

[Tuthmes]

Beef, thumes. Read the fucking thread

I did fgs. :<

I'm just not sure what kind of fusion beef would generate when it's mass is at 1 billion suns! I'm quite sure it would "just" collapse into itself and form a black hole.

 

[Wij]

Don't disagree with that. But considering a large lump of beef isn't currently undergoing fusion when it pops into existence with enough gravity to form a singularity then the singularity will get formed straight away. It's not going to "wait" until fusion's started - a black hole is going to form wherever the gravity is high enough.

Fusion would start outside of that - but because of the mass of the black hole (100 billion suns worth of mass) then you're going to have a heck of a gravity gradient...

The singularity will not form straight away. Something with the mass of a hundred billion suns at the level of density of beef will be spread over a huge area. The gravity from one side of it will be barely felt at the other. The collapse will not be instant. As the hydrogen and carbon atoms get forced together under the immense pressure that forms as the beef is crushed under its own gravity, they will undergo fusion. The more mass the more fusion. Things are not black holes just because of their mass, otherwise the galaxy would be one.

 

[Scouse]

I guess it boils down to how much gravity there would be at the centre of the fillet before it starts its rapid compression. If not enough to form the singularity then how long would it take to compress to that level?

Having squeezed beef, I reckon not very long at all.

Visualise it. It's surprisingly pleasing


Edit: As for the galaxy thing - beef's not got hundreds of light-years between individual protein strings, so it starts off reasonably dense in galactic terms...