Mass limit for pre-supernova stars

[BDanielMayfield]

What is the lower mass limit for stars destined to become Supernovae of the various classes?

Bruce

[starsurfer]

Not my area of expertise but I think it is more than 8 stellar masses.

[Ann]

What is the lower mass limit for stars destined to become Supernovae of the various classes?

Bruce

Like starsurfer, I'm not an expert here. But I, too, have heard that eight solar masses might be the lower limit for a star that will eventually go supernova.

However, when it comes to core-collapse supernovas, it is the evolution of the core that determines whether the star will go supernova or not. Massive stars may have extremely strong winds that possibly - possibly - may blow away so much of the outer parts of the star that the core will not be able to evolve to the point where it will explode. To go supernova, a star needs to go through a series of fusions, starting by hydrogen fusion and ending by silicon fusion that produces an iron core. But each new higher-element fusion needs a higher temperature to get going than the fusion that preceded it. Only very massive stars can compress their cores through the force of gravity to extract and concentrate the extremely high temperatures needed to get silicon fusion going. But a star that blows away much of its outer envelope may not be able to compress its own core to reach those temperatures, even if it started out with a very high mass.

Then again, stellar winds and stellar evolution may depend on different things. It wouldn't surprise me too much if only one of two stars that started out with the same mass will eventually go supernova.

For a star to produce a supernova type Ia, common wisdom says that you need a white dwarf that gathers mass from a bloated companion. For this to work, we probably need a relatively massive white dwarf, perhaps close to the upper limit when it comes to mass for a white dwarf, which is 1.4 solar masses. For both these reasons, we can see that the Sun can never go supernova. First of all, of course, the Sun doesn't have a companion. Let's say it were to pick up one a long time from now, after the Sun has become a white dwarf. But because the Sun will lose a lot of mass before it can become a white dwarf, its mass as a white dwarf will be no more than perhaps 0.5 or 0.6 solar masses. Even a bloated companion will not help it blow.

But there is a rather massive white dwarf quite close to the Sun, which is Sirius B. Its mass is 0.978 solar masses. Its companion, Sirius A, has a mass of 2.02 solar masses. But whether Sirius A will ever be able to dump enough mass on Sirius B to make it blow depends on, among other things, the separation of these two stars. Since the current separation varies between 8.2 and 31.5 AU, a strong future interaction between the two components doesn't seem likely unless the separation changes.

Ann

[BDanielMayfield]

Thanks starsurfer and Ann for those replies. I've been doing some of my own homework on this, learning more about these fascinating phenomena, and both of you are correct I think, at least to a first approximation.

Type Ia SN are caused by a runaway thermonuclear detonation of a white dwarf stellar remnant in which the core reaches a temperature hot enough to fuse carbon. In a non or slowly rotating white dwarf this occurs at what's known as the Chandrasekhar limit, where electron degeneracy pressure can no longer support the mass of the star. According to Wikipedia "the currently acccepted value for this limit is about 1.39 solar masses." This might be the lower mass limit for any kind of SN progenitor. Please comment to correct this if this assumption is incorrect.

But type Ia SN of larger masses are known to occur, for at least two reasons. The first is rapid rotation, in which centripetal effects cause more mass to be required before the core reaches detonation conditions. The second reason is the collision of a second body with the WD, which very briefly produces a WD of more than the Chandrasekhar mass limit. The most massive Ia SN observed to date is thought to have been about 2 solar masses before it popped, and to have been the result of the collision of two WDs.

Bruce

[BDanielMayfield]

Not my area of expertise but I think it is more than 8 stellar solar masses.

(I know you meant to write solar.)

Some may wonder how I could refer to both starsurfer's and Ann's answers as being correct, when one was 8, and the other was 1.4 solar masses. Fear not, no fuzzy math here. I had asked about the lower mass limit for the differing classes (I see now that I should have used the word types instead) of SN. Ann gave a detailed answer re one very important type of SN, Ia, which have a different cause than all the other types.

8 solar masses is a good starting point for a lower limit for stars that can form SN due to the other major cause, which is core collapse.

Bruce

[rstevenson]

Bruce, the Wikipedia article on Supernovas includes a chart with a breakdown of the different results when stars of different masses and metallicities go nova. See http://en.wikipedia.org/wiki/Supernova#Core_collapse, in particular.

Rob

[BDanielMayfield]

Bruce, the Wikipedia article on Supernovas includes a chart with a breakdown of the different results when stars of different masses and metallicities go nova. See http://en.wikipedia.org/wiki/Supernova#Core_collapse, in particular.

Rob

That's a great reference for this question Rob, many thanks. It confirmed starsurfer's and Ann's recollections about 8 solar masses being the lower limit I was asking about:

Stars with initial masses less than about eight times the sun never develop a core large enough to collapse and they eventually lose their atmospheres to become white dwarfs.

But then later, if the WD accretes enough mass as Ann discussed, it still may become a SN if it grows to over 1.39 solar masses, but that largely depends on whether it has a close stellar companion or not.

That chart you mentioned is enormously informative Rob. I tried to copy it into this comment without success, but it can be viewed in Rob's above Wikipedia link.

I started this topic because I was wondering about SN occurrence rates and what can be reasonably predicted about any given star, based on its mass. I've learned that much depends on the star's elemental composition, in addition to its mass. Also, as the chart Rob mentioned shows, you can't simply say that any given star of more than 8 solar masses is destined to become a SN someday. For some stars of certain masses it's like in monopoly when you draw the go directly to jail card, only much worse: do not blow your top, go directly to blackholeness.

Bruce

[MargaritaMc]

This book might interest you, Bruce.

David   S.   Stevenson
Extreme Explosions
Supernovae, Hypernovae, Magnetars, and Other Unusual Cosmic Blasts
10.1007/ 978-1-4614-8136-2
Springer Astronomers' Universe series 2014

M