# How big can a body get (size wize) before it collapses onto itslef?

1. Nov 16, 2007

### rubecuber

Hey guys, how big can a body get before it collpases upon itself and becomes a black hole? I'm not asking about how heavy it must be to become a black hole (Chandraker told me that) but just simply how massive a body can get

2. Nov 17, 2007

### matt.o

The thing that really matters is the density. For example, galaxy clusters weigh about $$10^{15}$$ solar masses, yet they don't "collapse upon" themselves. Can you be more specific with your question? Like what do you mean by "collapse upon itself"? Form a black hole, or not be a part of the Hubble flow and become gravitationally bound?

Last edited: Nov 17, 2007
3. Nov 17, 2007

### malawi_glenn

It depends on its composition and so on.

But there is a limit of about 150 solar masses for stars, then they become unbound due to radiation pressure.. (assumes you start building your star from ordinary interstellar media, like solar composition)

So you have the limit there I guess.

But please specify, are you talking about some theoretical thing like "how bid iron sphere you can build" or like I indicated, how big can stars become?

4. Nov 17, 2007

### rubecuber

Malawi glenn, i'm talking about how big stars can become

5. Nov 17, 2007

### malawi_glenn

Great: then the limit is approx 130-150 solar masses due to high radiation pressure. See Prialnik: "Introduction to stellar structure and evolution" Cambridge university press, chapter 7. For example..

6. Nov 17, 2007

### rubecuber

matt.o i'm talking abouit before it becomes a black hole, and i'm talking about 1 individual objeect, not a galaxy cluster

7. Nov 17, 2007

### malawi_glenn

You cant shut of fusion just like that. You must take into account for other things when dealing with real objects. Otherwise it depends on density, a pea could become a black hole if it had enough density.

If you mean Chandraseackar, the chandraseackar limit is just when electron degenarcy pressure cant hold anymore, i.e it is the boundray for becoming a neutron star.

8. Nov 17, 2007

### Chris Hillman

Everyone: the name is Chandrasekhar. Sheesh! :grumpy:

Consider supernova remnants. They may form white dwarf stars, neutron stars, or black holes. The Chandrasekhar limit gives an upper limit for how massive the core can be in order to form a white dwarf star. The upper limit for how massive the core can be in order to form a neutron star is not yet known as precisely, due to lack of knowledge of the equation of state of "neutronium". However, it is thought to be around three solar masses; see http://www.astronomy.ohio-state.edu/~ryden/ast162_5/notes21.html

As already pointed out, if we consider stars which are still burning nuclear fuel, much more massive stars can exist. I was talking about what happens when this fuel is exhausted.

Last edited: Nov 17, 2007
9. Nov 17, 2007

### malawi_glenn

Freak! His name is hard to spell, this is a forum, not the Nobel Party. The most important is that we understand each other, even though the first guy spelled Chandraker, i know who he meant, because the thing we discuss here is the physics.

10. Nov 17, 2007

### rubecuber

thanks malawi, and all others you guys are great!

11. Nov 18, 2007

### Chris Hillman

I know you both mispelled his name, and that seemed sufficiently worrisome that I spoke up. PF caters to a very diverse group of users, obviously; I paid you an oblique compliment by assuming that you are physicist in training, in which case I think it's important to help inculcate good citation habits as soon as possible. More generally, yes, we all figured out who you and the OP meant, but I am concerned by the decline in spelling and grammatical standards which makes many recent posts essentially illegible, so I feel that even the youngest people at PF should be encouraged to try to formulate their thoughts clearly and to write well. After all, whatever they wind up doing in life, changes are good that an ability to write a crisp and concise memo will serve them well. In the most extreme cases, in encouraging newbies to write clearly one has to being by encouraging them to try to obey such basic rules as (mostly) correct spelling and grammar.

In short, my intentions are good.

12. Nov 18, 2007

### malawi_glenn

Your intentions are good, yes, but you dont have to get mad/angry.

Also many here are not from England, Usa or Australia, so their grammar might not be the best. But I admitt that some posts are quite awful to read, and some posts have much "chatt" language, as u btw w8 etc, that is not so fun..

But if you want to "complain", dont do it on me...I am not a newbie nor have the worst language here. So play cop with the newbies instead of me, you are just making me quite pissed off..