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a topic for debate


danielost

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i was watching eureka today.

the question is how small can a star be, physically not mass, before it becomes a black hole. i know a star has to have a certain amount of mass, but how small can that mass fit into before the gravity of said mass would just convert it into a black hole.

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I don't know if I understand your question, but I will throw stuff out anyway. Size and mass are two different issues. A star that is about 1.4 times the size of our sun is the limit(The Chandrasekhar Limit) as to what will happen when the sun burns its fuel and heads towards the end of its life.

Smaller than the 1.4 solar units(our sun=1.0 solar units) and a dying star will end up becoming a white dwarf...which can be just slightly larger than our earth(that is a lot of squishing).

Larger than 1.4 SU, and one of two things happen, as the star falls in on itself it can either blow up(neutron star) or become a black hole...

Edited by Fluffybunny
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I don't know if I understand your question, but I will throw stuff out anyway. Size and mass are two different issues. A star that is about 1.4 times the size of our sun is the limit(The Chandrasekhar Limit) as to what will happen when the sun burns its fuel and heads towards the end of its life.

in the show, their sun was about the size of a basketball. yes i know that size and mass are two different things. i know more or less what happens to a star at the end of it's life. it either goes nova, as our star will, or it will go super nova, as most stars with a mass of 10 times our star will do.

but what i am asking is how small would a star lets say the mass of our sun can be, before the mass of that star would just go ahead and crush it into a black hole.

i know that the max size of a gas giant is around what jupiter is. however the mass can be a lot higher.

Edited by danielost
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Suns between 3-15 solar masses can end up black holes...Super dense stuff...even the less dense white dwarfs have insane densities...I recall that a cup full of the stuff that makes a dwarf would weigh hundreds of millions of tons. Micro black holes have the mass of the moon, but are smaller than a pencil lead in diameter...

Off the top of my head, a single solar mass black hole is about 40 miles across, as to how large the sun would be when it was collapsing past the point of no return, I am not sure...

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Suns between 3-15 solar masses can end up black holes...Super dense stuff...even the less dense white dwarfs have insane densities...I recall that a cup full of the stuff that makes a dwarf would weigh hundreds of millions of tons. Micro black holes have the mass of the moon, but are smaller than a pencil lead in diameter...

Off the top of my head, a single solar mass black hole is about 40 miles across, as to how large the sun would be when it was collapsing past the point of no return, I am not sure...

i am thinking if the sun was shrunk to about the size of a golf ball it would become a blackhole. but that is only a guess no math behind it.

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i am thinking if the sun was shrunk to about the size of a golf ball it would become a blackhole. but that is only a guess no math behind it.

Well if a single solar mass sun(i.e. our sun) ends up being about 40 miles in diameter as a black hole, my guess would be that a golf ball isn't going to happen...

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Well if a single solar mass sun(i.e. our sun) ends up being about 40 miles in diameter as a black hole, my guess would be that a golf ball isn't going to happen...

ok so at 41 miles in diameter it would still be a normal glowing star?

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i know more or less what happens to a star at the end of it's life. it either goes nova, as our star will, or it will go super nova, as most stars with a mass of 10 times our star will do.

Just to address this point, our sun is not considered massive enough to go nova. The current theory is that it will expand into a red giant with most of it's outer layers drifting out into space to form a nebula. After this, what remains will collapse to the size of a few thousand miles in diameter, becoming a white dwarf.

When it has dissipated it's remaining heat after a few billion years it will then become a black dwarf, essentially a dead star.

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Just to address this point, our sun is not considered massive enough to go nova. The current theory is that it will expand into a red giant with most of it's outer layers drifting out into space to form a nebula. After this, what remains will collapse to the size of a few thousand miles in diameter, becoming a white dwarf.

When it has dissipated it's remaining heat after a few billion years it will then become a black dwarf, essentially a dead star.

that is what a nova is. a nova doesnt blow up it expands up. a super nova blows up. the other difference is that any stars that form from a nova cloud would be stuck with elements smaller than iron. where as a super nova produces the heavier elements.

Edited by danielost
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that is what a nova is. a nova doesnt blow up it expands up. a super nova blows up. the other difference is that any stars that form from a nova cloud would be stuck with elements smaller than iron. where as a super nova produces the heavier elements.

Sorry. I misread your post. I could have sworn that I read super nova. Why I confused that with nova I've no idea.

I'll crawl back in my box now.

Edit: I'll learn to type one of these days as well.

Edited by Kroe
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ok so at 41 miles in diameter it would still be a normal glowing star?

No. the 40 miles across I mentioned was as a black hole, the very large stars collapse down to that small size when they run out of fuel to keep burning. It is at the end of their lives that they go through this process, so they would not be a "normal glowing star" either way. Depending on how massive they are they can become white dwarfs or if they are massive enough, then they can become black holes...either way, they are at the end of their lives...

Stellar evolution is a lot of work and pretty detailed, so to go from scratch to the mathematics required to calculate thresholds of black holes is pretty advanced stuff.

Wiki goes over the topic very basically, to give you an idea. University of Michigan also has some intro information too...

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Sorry. I misread your post. I could have sworn that I read super nova. Why I confused that with nova I've no idea.

I'll crawl back in my box now.

Edit: I'll learn to type one of these days as well.

no dont crawl back in your box. i did say super nova but i used it in connection with super massive stars. all ideas are good even bad ones, it keeps people on their toes. besides if you never make a mistake you dont learn much.

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No. the 40 miles across I mentioned was as a black hole, the very large stars collapse down to that small size when they run out of fuel to keep burning. It is at the end of their lives that they go through this process, so they would not be a "normal glowing star" either way. Depending on how massive they are they can become white dwarfs or if they are massive enough, then they can become black holes...either way, they are at the end of their lives...

Stellar evolution is a lot of work and pretty detailed, so to go from scratch to the mathematics required to calculate thresholds of black holes is pretty advanced stuff.

Wiki goes over the topic very basically, to give you an idea. University of Michigan also has some intro information too...

i know that the math is super hard and above my head, i also know that there are some super smart people on here who are able to do that math. dont know if that math can be done in a day, an hour or 14 years.

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I don't know if I understand your question, but I will throw stuff out anyway. Size and mass are two different issues. A star that is about 1.4 times the size of our sun is the limit(The Chandrasekhar Limit) as to what will happen when the sun burns its fuel and heads towards the end of its life.

Smaller than the 1.4 solar units(our sun=1.0 solar units) and a dying star will end up becoming a white dwarf...which can be just slightly larger than our earth(that is a lot of squishing).

Larger than 1.4 SU, and one of two things happen, as the star falls in on itself it can either blow up(neutron star) or become a black hole...

I don't believe they blow up to become Neutron Stars. (I know theory states a Supernova happens first, and then a Neutron star is left behind, but my belief on this matter is that the expansion of the inner core simply causes the exterior to explode outward--therefore, the actual core that becomes the remaining Neutron Star does not ever explode). Neutron Stars, to my understanding are just supermassive, tiny-diametered fairly dormant stars. They are approximately 18 miles in diameter, but about 1.5 times the mass of our sun.

As for your limit of 1.4 times the size of our Sun, I believe that only applies to the Iron core of a massive star, not the entire diameter.

Edited by Watchers
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I don't believe they blow up to become Neutron Stars. (I know theory states a Supernova happens first, and then a Neutron star is left behind, but my belief on this matter is that the expansion of the inner core simply causes the exterior to explode outward--therefore, the actual core that becomes the remaining Neutron Star does not ever explode). Neutron Stars, to my understanding are just supermassive, tiny-diametered fairly dormant stars. They are approximately 18 miles in diameter, but about 1.5 times the mass of our sun.

As for your limit of 1.4 times the size of our Sun, I believe that only applies to the Iron core of a massive star, not the entire diameter.

the 1.4 deals with the mass of the star, not any given size or diameter...nuetron stars vary in size based on what the star was that produced them; the more massive stars generate smaller neutron stars than do the less massive stars(as the more massive stars have a greater mass to collapse and in the end can collapse to a higher density than smaller stars)...kind of backwards from what you would think, but that is what they do.

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ok so at 41 miles in diameter it would still be a normal glowing star?

You can calculate the Schwarzschild radius for any mass (i.e. how small of a radius you'd have to cram the mass into before it collapses into a black hole) here.

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You can calculate the Schwarzschild radius for any mass (i.e. how small of a radius you'd have to cram the mass into before it collapses into a black hole) here.

didnt have to do the math they tell you right there what i wanted to know. you can crush the sun down to 4km and it will still glow as it does now. drop it to 3km and it becomes a black hole. by the way drop the earth to 9mm and it becomes a black hole.

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That about sizes it up eah?

In an alt- universe maybe that Stars are the size of a few atoms,with all things equal the sub-sub atomic world maybe.

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I remember reading an article (years ago) that they found a star that's smaller than Jupiter.

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I remember reading an article (years ago) that they found a star that's smaller than Jupiter.

Sally Struthers?

No wait, she's neither a star nor smaller than Jupiter. rofl.gif

Is this what you read?

Newfound Star Smaller than Some Planets

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If black holes are created from something collapsing then how come some people are saying the LHC will create blackholes if particles are being smashed together?

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Its all in the Gravity of ? Hum Well the Gravity of everything!

Its actually what makes everything Sorta Like a Fatal attraction!

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If black holes are created from something collapsing then how come some people are saying the LHC will create blackholes if particles are being smashed together?

the lhc was designed to create mini blackholes which last for a couple of seconds. what those people are thinking is one of the blackholes will get to big and start pulling the earth into it.

the problem is even if the sun was shrunk down to the 9km to make it a blackhole, its event horizen would not be any bigger the size of the sun's current size.

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the problem is even if the sun was shrunk down to the 9km to make it a blackhole, its event horizen would not be any bigger the size of the sun's current size.

That `9km' size is the Sun-turned-black-hole's event horizon.

The actual `size' of the Sun-turned-black-hole is unknowable (since it is behind the event horizon), and quite possibly meaningless.

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That `9km' size is the Sun-turned-black-hole's event horizon.

The actual `size' of the Sun-turned-black-hole is unknowable (since it is behind the event horizon), and quite possibly meaningless.

your right. but at some point the sun has to hit the 9km size as a normal glowing sun. 2 seconds later it is a singularity.

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