Mystery of Type 1a Supernova: No Hydrogen in Spectrum

[Math Is Hard]

This is something that mystifies me --
If the first stars were composed of only hydrogen and helium, why does a Type 1a Supernova show virtually no hydrogen in its spectrum? It seems logical that we would see an abundance of hydrogen.
Thanks!

 

[Nereid]

Type 1a supernovae are thought to be white dwarf stars. A white dwarf is what's left of a star once the hydrogen in its core has been burned, and the remaining hydrogen expelled into interstellar space, as part of the last phase of hydrogen burning (several mechanisms).

This suggests that there was a time in the early universe when there were no Type 1a supernovae - ~solar mass stars take some time to evolve into white dwarfs, and more massive stars don't end their lives as white dwarfs!

 

[Math Is Hard]

Oh, ok, that makes sense now. The hydrogen has already been depleted. Thanks!

 

[marcus]

Originally posted by Math Is Hard
Oh, ok, that makes sense now. The hydrogen has already been depleted. Thanks!

You and Nereid didnt get to the good part yet.
So there is this white dwarf, composed say of carbon and nitrogen, and no longer fusing because it does have mass enough to create the core conditions to fuse carbon

So it is just sitting there gradually cooling, which is all that an isolated white dwarf can do. What makes it suddenly explode into a Type Ia supernova?

 

[Math Is Hard]

hmmm... well, I only know a tiny bit about this, but I am told that white dwarves have a mass limit, and that once they reach this limit they become unstable and undergo a gravitational collapse. But I am not sure how a white dwarf gets to that limit and what exactly is causing the mass increase.
Do tell!

 

[mathman]

Type Ia supernovae are produced when a white dwarf sucks matter off of a red giant companion, reinitiating fusion. The entire white dwarf is literally blown to bits -- there is no compact object (neutron star or black hole) left over, like there can be in Type I or II supernovae.

Sucking off matter from a red giant is correct. However, I believe the rest of your picture is somewhat misleading. The mass increase eventually (fusion is irrelevant) will reach the point where it cannot remain a white dwarf, and collapses into a neutron star. This triggers the type Ia explosion.

 

[theEVIL1]

Originally posted by Ambitwistor
Type Ia supernovae are produced when a white dwarf sucks matter off of a red giant companion, reinitiating fusion. The entire white dwarf is literally blown to bits -- there is no compact object (neutron star or black hole) left over, like there can be in Type I or II supernovae.

A link:

http://www.astronomyinfo.pwp.blueyonder.co.uk/Supernova.htm

I think you mean in a Type II SN. NO Type I leaves anything behind as the Core is converted into energy. In a Type II (Core rebound) there is always at least something left.

 

[meteor]

Type Ib supernova can let a white dwarf after the explossion (that can develop to a neutron star or black hole)

 

[Labguy]

Originally posted by Ambitwistor
Thanks. I was hedging: I thought I remembered reading that some type I (not Ia) supernovae could undergo gravitational collapse (do you know if this is true?), so I thought there might be something left over.

They all undergo gravitational collapse; this is where the "initiating" energy comes from.

But, in the case of a Type Ia supernova, a very small percentage of accreting white dwarfs will become type Ia's. The "chemical conditions" of the Dwarf are specific and rather rare. The Dwarf must be composed mainly of Carbon and Oxygen (sometimes Si). Also, the mass limit for the supernova is ~1.38 - 1.39 Solar masses, not the "standard" 1.44 Chandra's limit. The Carbon is the catalyst, and it must detonate or burn (deflagration) at a specific rate to cause the energies required for the total fusion of all material into the heavier elements, leaving no core remnant at all.

This was discussed at length (I think) in an older thread several months ago. S. E. Woosley is considered the foremost "expert" on Type Ia supernova since he has spent his entire career on the subject, and there are still uncertainties about which carbon "detonation-deflagration" models are most likely. Quite a bit about these can be found at:

http://www.journals.uchicago.edu/ApJ/journal/issues/ApJ/v475n2/33428/33428.html

Click on "Introduction" first.

Labguy

 

[Glenn]

For anyone interested, there is a relatively new book out which has a bit of discussion about type 1A Supernova. The book is, "Alpha and Omega: The Search for the Beginning and End of the Universe"
by Charles Seife

-Glenn