possible intermediate between supernova and hypernova

[Martin]

this is being reported as an explosion which was intermediate between a supernova collapse (say to form a neutron star) and the more powerful event called a Gammaray Burst (GRB), or sometimes a hypernova.

 

http://www.sciam.com/article.cfm?id=supernova-2008d-missing-link&sc=rss

 

the SciAm article calls it a "missing link"

 

Some models of GRB involve collapse to form a black hole.

 

I dont know enough to evaluate how appropriate it is to say missing link. I guess the hope is that studying the event will reveal something about what causes GRB. There definitely are at least two different classes of powerful explosions---SN and GRB

and there are different types within those classes.

 

Maybe someone wants to find us some good links and kind of outline the situation----provide some perspective on whether this 'missing link' event is significant or not?

[Arch2008]

I read the link, which doesn’t offer a lot of info, however this is the general explanation of these massive star implosions. The largest stars were first discovered by two Frenchmen, Charles Wolf and George Rayet.

http://en.wikipedia.org/wiki/Wolf-Rayet_star

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980603a.html

 

As more of these stars were found, a category named after the discoverers was created. Wolf-Rayet stars are further categorized by their elemental make-up. Giant stars fuse hydrogen into many other elements and almost all of the elements are created during the explosion of these stars. Three types of WR stars are known, those that contain mostly carbon, denoted as WC, those dominated by nitrogen (WN), and those rare WR with a large mix of carbon and oxygen (WO).

http://cfa-www.harvard.edu/~pberlind/atlas/htmls/wrstars.html

 

(The elements in a star can be determined from the star's light using emission spectroscopy.)

http://en.wikipedia.org/wiki/Emission_spectroscopy

 

This rather unique event mentioned in the article may have been a rare WO star going nova. The star was most certainly a WR star, since they shed a cloud of hydrogen before they explode. This is also indicated because it was a Type Ib supernova (with oxygen lines).

http://en.wikipedia.org/wiki/Type_Ib_and_Ic_supernovae

 

That would be my guess.

[Martin]

I read the link, which doesn’t offer a lot of info, however this is the general explanation...

 

This rather unique event mentioned in the article may have been a rare WO star going nova. The star was most certainly a WR star, since they shed a cloud of hydrogen before they explode. This is also indicated because it was a Type Ib supernova (with oxygen lines).

http://en.wikipedia.org/wiki/Type_Ib_and_Ic_supernovae

 

That would be my guess.

 

Good work. Thanks for assembling background on this. As you say, the popular article didn't say too much. Here, in case you are interested, is the journal article that was published in Science about this.

You can download the PDF at this link:

http://arxiv.org/abs/0807.1695

The metamorphosis of Supernova SN2008D/XRF080109: a link between Supernovae and GRBs/Hypernovae

Paolo A. Mazzali,...

22 pages, 7 figures. Accepted for publication in Science

(Submitted on 10 Jul 2008)

 

"The only supernovae (SNe) to have shown early gamma-ray or X-ray emission thus far are overenergetic, broad-lined Type Ic SNe (Hypernovae - HNe). Recently, SN 2008D shows several novel features: (i) weak XRF, (ii) an early, narrow optical peak, (iii) disappearance of the broad lines typical of SNIc HNe, (iv) development of He lines as in SNeIb. Detailed analysis shows that SN 2008D was not a normal SN: its explosion energy (KE ~ 6*10^{51} erg) and ejected mass (~7 Msun) are intermediate between normal SNeIbc and HNe. We derive that SN 2008D was originally a ~30Msun star. When it collapsed a black hole formed and a weak, mildly relativistic jet was produced, which caused the XRF. SN 2008D is probably among the weakest explosions that produce relativistic jets. Inner engine activity appears to be present whenever massive stars collapse to black holes."

[Arch2008]

WR stars start as blue supergiants that inflate to red supergiants. If they have a mass of 30-35 Suns, as SN 2008D did, then they go to the WR phase. After a million years or so the WR's explode/implode. Theoretically, one could simply implode to a blackhole without causing any explosion. The process is not well understood, because no WR has been observed before imploding. The emission spectroscopy lines of ejecta from supernovae match that of old WR stars, so “if it quacks like a duck”… There are only about a handful of the WO stars in all of the Milky Way, that is why I believe that a very rare SN may have originated from a very rare star. We’ll see.

[Martin]

I've gotta say I value this kind of reaction. It makes it more fun and teaches me some things I didn't know.

There is another thing I'd like to know your reaction to from not too long ago, though I think it was before you joined us. I'll see if I can find it.

 

Here it is!

http://arxiv.org/abs/astro-ph/0612617

It was something about 150 solar masses. What could allow a star to get so massive without its own light driving away the matter it was trying to pull in. And why did it fail to shed its envelope, at life's end?

The idea of PAIR INSTABILITY gets into it, if I remember. When light gets hot enough a new kind of scattering kicks in which makes it all the harder for the light to escape from the core. A new kind of opaqueness. I recall talk of that, also the idea that very early stars don't have as much Carbon to initiate the CNO cycle so they can reach greater masses. This is vague recall, I dont have time to check my links right now. I'll just toss the stuff out in case it means something

http://en.wikipedia.org/wiki/SN_2006gy

http://spaceflightnow.com/news/n0705/07supernova/

You are not being put on the spot! If you feel like clarifying what was going on with SN2006gy, or have any comment, that's great. If no comment, that's fine too.

My memory of this may be quite wrong. Dont have time to check.

 

Oh yes, another thing was the March 19 burst detected by Swift, GRB080319B

http://www.sciencedaily.com/releases/2008/03/080321093110.htm

the principal investigator was Gehrels, so i could probably find a journal article on arXiv that talks about this, if you'd like

 

Any comment would be appreciated.

Edited July 31, 2008 by Martin

[Arch2008]

I'll give it a look!

 

The effect you mention, that a huge star’s own light prevents it from growing to even more enormous size, is the Eddington Limit.

http://en.wikipedia.org/wiki/Eddington_limit

 

I was able to find this link that somewhat explains how stars below this limit grow so large.

http://www.livescience.com/space/scienceastronomy/080227-massive-stars.html

 

As well as how large they may become.

http://www.3towers.com/sGrasslands/Essays/HeavyStar/HeavyStar01.asp

 

Essentially, at some point, the explosive force of the core counteracts the star’s own force of gravity, so that its outer surface attains zero gravity (that felt by astronauts in space) and the surface mass starts floating away.

 

In James Kaler’s book “Extreme Stars” he addresses what he labels Hypergiants. Normally large stars, like Red Supergiants (RSG) or Large Blue Variables (LBV) fuse hydrogen into heavier so called metallic elements like helium, carbon, nitrogen and oxygen. This fusion releases energy according to Einstein’s equation. This energy counteracts the enormous gravity of these giants to keep the star from collapsing totally. However, once iron is created at the core, this process stops. It takes energy to fuse lighter elements into iron. At this point, the outer layers of the star collapse inward and bounce off the iron core, creating a shock wave ending in some form of nova. Depending on the force of the inward collapse, several outcomes can occur. If the iron core is squeezed to the point that the atom’s electrons are as tightly packed as is possible (called electron degeneracy), then a white dwarf star is the result. If the protons and electrons are crushed together into neutrons, then the star pretty much becomes an atomic nucleus the size of a city, called a neutron star. Finally, the core can become a singularity in a black hole.

Hypergiant stars don’t follow this path. The core of a hypergiant is so compact that in addition to normal fusion, particle pairs are also created in abundance. At some critical point, particle-antiparticle pairs are annihilating at such a rate that the resulting gamma rays superheat the star’s core and it erupts (pair instability). The energy of this eruption tears the star apart from the core outwards. No core mass remains to implode into anything else.

As you mention, they allude to the possibility that the star was low on certain elements and this could have caused the hydrogen envelope to remain in tact. The hydrogen added to the astounding luminosity of the SN.

[Arch2008]

P.S. I just read in Astronomy magazine that two astronomers named Leahy and Ouled think that 2006gy may have created a super dense remnant they called a quark star.

 

http://www.astronomy.com/asy/default.aspx?c=a&id=7037