Red giant

[MadaBidyoni]

Hi

how could i know which massive stars will become a red giant & then a supernova

& which will collapse straight to a supernova?

what will be with a 30 solar masses star?

thanks

[brantuk]

There's a list of really really big stars on this page along with more info than I could put in a post here:

http://en.wikipedia.org/wiki/List_of_most_massive_stars#List_of_the_most_massive_stars

Also pictorially here:

http://centralastronomyclass.pbworks.com/w/page/15400622/Evolution%20of%20Stars%20Greater%20Than%2030%20Solar%20Masses%20aka%20Massive%20Stars

Hth

[LouisJB]

Most stars with a main sequence mass greater than about 11 solar masses will produce supernovas at the end of their life. More specifically when the iron core exceeds about 1.4 solar masses (Chandrasekhar limit) then this is essentially guaranteed. The core will not be supported by electron degeneracy and can only be supported by neutron degeneracy pressure, hence making a very dense neutron star. There are type I and II supernova variants (and also nova too, which is not related directly to supernova).

Stars with lower initial mass that don't meet the above will produce a white dwarf in their final stages as a planetary nebula is shed from the outer layers

Why do you ask? Betelgeuse is our nearest and most likely next supernova, it's currently a supermassive red giant. It's angular size has even been resolved by large telescopes, it's that big (and close)!

[cantab]

Personally I tip Eta Carinae to go before Betelgeuse. And I expect we'll all be booking last-minute holidays if it does!

[Sandancer10]

There's a list of really really big stars on this page along with more info than I could put in a post here:

http://en.wikipedia.org/wiki/List_of_most_massive_stars#List_of_the_most_massive_stars

Also pictorially here:

http://centralastronomyclass.pbworks.com/w/page/15400622/Evolution%20of%20Stars%20Greater%20Than%2030%20Solar%20Masses%20aka%20Massive%20Stars

Hth

Great topic and the link you suggested is good - I can hear my printer whirring now. 

[MadaBidyoni]

Most stars with a main sequence mass greater than about 11 solar masses will produce supernovas at the end of their life. More specifically when the iron core exceeds about 1.4 solar masses (Chandrasekhar limit) then this is essentially guaranteed. The core will not be supported by electron degeneracy and can only be supported by neutron degeneracy pressure, hence making a very dense neutron star. There are type I and II supernova variants (and also nova too, which is not related directly to supernova).

Stars with lower initial mass that don't meet the above will produce a white dwarf in their final stages as a planetary nebula is shed from the outer layers

Why do you ask? Betelgeuse is our nearest and most likely next supernova, it's currently a supermassive red giant. It's angular size has even been resolved by large telescopes, it's that big (and close)!

but before the supernova it will not get to be a red super  giant?

[LouisJB]

Personally I tip Eta Carinae to go before Betelgeuse. And I expect we'll all be booking last-minute holidays if it does!

Quite possibly, both are very good candidates. Maybe it already did go (either, or both!). Eta Carinae is over 10x further away that Betelgeuse so if anything it should be less of a concern. I think we should be fine from either in any case, but Betelgeuse is a mere 642ly so it will be a 'close one' when it does go

[LouisJB]

but before the supernova it will not get to be a red super  giant?

When what goes, Betelgeuse? It's already a Red supergiant and more generally, the process of forming any supergiant (or a red giant) is 'very slow' relative to the rapid explosion of a supernova.

Supergiants come in all flavours from blue to red (yellow etc) and are just clarified by their spectra / temperature. There isn't a clear-cut line between a red giant and a (red) supergiant, but red giants have their own designation on the H-R diagram (RGB, AGB) whereas supergiants are basically massive stars evolved off of the main sequence - the exact definition is not so well defined.

There's a whole range of stars based on size, from dwarfs (red, brown, white) through sub-dwarfs right up to the hypergiants. The most important thing is how much mass will dictate the speed through the main-sequence (along with the colour and luminosity) and the end result being planetary nebula and white dwarfs for lower mass stars or ending abruptly in some form of supernova for more massive stars. Low mass star candidates that don't quite make it are brown dwarfs. The more massive the star the brighter and bluer it burns and the shorter its lifespan. Stars leave the main-sequence in what is called main-sequence turn-off, which is a way to age things like globular clusters.

Have a good look at the H-R diagram, you'll find the various classifications there. It's two dimensional, temperature (or spectra) vs. mass, the 3rd 'dimension' for a particular star being the age of the star, the combination will indicate where a star is in it's lifecycle and what 'type' it is. For any given point the evolution is quite well defined, but of course the transition regions are sensitive to mass. For example some stars could be right on the balance between producing a supernova and ending with a planetary nebula and their exact fate might depend how much mass is shed in the final unstable years before finally ending up in one of the possible final states of stellar evolution.

I'm no expert, this is just my understanding put in a few words. There are many subtleties involved and not all processes are totally understood either. The essential thing is stars form out of gravitational collapse, into protostars, generally move along Hayashi tracks towards the main sequence (where they spend the bulk of their lifespan) and then move from the main-sequence to a number of different types of transition. Everything is very mass-sensitive, but particularly the final stages since it dictates what type of stable nuclear states can be supported against the force of gravity. Massive stars finish with very unstable states and the final supernova happens 'very rapidly' as the core collapse reaches a big crunch when the repulsion of Fermions (exclusion principle) rapidly stops the what was an accelerating gravitational collapse. This results in a violent outgoing shockwave we classify is some form of supernova or hypernova. Interestingly this outgoing shockwave can be the trigger for new star-birth in the surrounding interstellar medium if it is near the right initial conditions (see Jeans mass).