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Fraser
2007-Nov-01, 04:40 PM
There are a few ways that stars can go kaboom, and each variant is different enough that astronomers can figure out what kind of object detonated as a supernova. ...

Read the full blog entry (http://www.universetoday.com/2007/11/01/colliding-white-dwarfs-caused-a-powerful-supernova/)

antoniseb
2007-Nov-01, 07:04 PM
I recall saying that the fast-spinning white dwarf scenario was a bit unlikely... but better still this article tells us a way to tell the difference between these white-dwarf collisions, and normal type 1a supernovae! Very nice.

mfumbesi
2007-Nov-02, 12:53 PM
The universe is infinity interesting!

Doodler
2007-Nov-02, 01:54 PM
I recall saying that the fast-spinning white dwarf scenario was a bit unlikely... but better still this article tells us a way to tell the difference between these white-dwarf collisions, and normal type 1a supernovae! Very nice.

So what would these be? Type 1c?

antoniseb
2007-Nov-02, 02:23 PM
So what would these be? Type 1c?
1c is already taken. This type would need a new designation.

Jerry
2007-Nov-02, 02:54 PM
I recall saying that the fast-spinning white dwarf scenario was a bit unlikely... but better still this article tells us a way to tell the difference between these white-dwarf collisions, and normal type 1a supernovae! Very nice.

They are trying very hard to preserve the model and make this a unique event, but how can there be only one binary solution? As John Middleditch has pointed out, we will see binary events from many different prospectives, so the lightcure width, polarity, and magnitude are all functions of both total mass and composition and very importantly, the viewing angle.

http://arxiv.org/PS_cache/astro-ph/pdf/0608/0608386v17.pdf


The unexpected faintness of distant Type Ia Supernovae (SNe) has been used to argue for an accelerated expansion of the universe, with the understanding that these are thermonuclear disruptions of accreting white dwarfs. However, the high velocity and polarized features observed in SNe Ia, and their inverse relation to luminosity, particularly for polarization, are consistent with an extreme version of the axisymmetry now seen in SN 1987A, which could be the result of doubledegenerate merger-induced core-collapse.

Middleditch pointed out many of the features observed in many 'type Ia' collisions, such as the polarity and velocity, are more consistent with binary events than the standard 'type Ia' model. We have seen a number of binary pairs of white dwarfs in our own galaxy, so as a whole the universe should be quite rich with them. There is also the confusing scenario where we may view a binary event where the star closest to us is a white dwarf, and a companion collapsing into the fray is not.

http://www.bautforum.com/newreply.php?do=newreply&p=1102820



Ia’s in old populations are almost exclusively due to CO-CO WD merger. In younger populations they can also be merging CE binary WR stars. Occam’s Razor and the extreme bipolarity of Ia’s implied by their HVFs and IPL polarizations would suggest that Ia’s observed from the DD merger poles are Type Ic SNe, given enough overlayer to shroud the TN ashes of Si, S, & Fe (otherwise per the Abstract). Thus Ia/c’s form a continuous class of SNe, varying only by overlayer mass and observer co-i.

This is a concern for Ia Cosmology, as small levels of Ibc contamination can spuriously produce a high fraction of the [apparent cosmic acceleration]...
Have overdiligent attempts to select a local sample of Ia’s “uncontaminated” by Ic’s, excluded events in error by a tenth to a whole magnitude, which are not routinely excluded from distant samples? There appears to be a gap between the Ia’s underluminous by 1-2 whole magnitudes, which are easily excluded by the TiII ll 4,000-4,500 Å shelf, and the others in the local sample. Are there Ia’s in this gap which may not be so easily exluded from the distant samples? Time will tell.

But Middleditch and others, casting severe doubt upon the model developed over the last fourty years, have been unable to get papers published. Cherry picking the features of SN 2006gz that seem to set it apart may preserve the illusion for a while, but the mold is broken.

http://www.cfa.harvard.edu/press/2007/pr200729.html


"Supernova 2006gz stands out from normal Type Ia objects and wouldn’t be included in cosmology studies," commented Hicken. "But we have to be careful not to mistake a double white dwarf explosion for a single white dwarf blast. SN 2006gz was easy to recognize, but there may be less clear-cut cases."

You heard it first, here.

antoniseb
2007-Nov-02, 03:30 PM
... Cherry picking the features of SN 2006gz that seem to set it apart may preserve the illusion for a while ...

I think the most obvious feature that sets 2006gz apart is that it was brighter, and produced more nickel-56 than the normal type 1a SNe. What this study did was show that there were other observable differences too, and that they matched models for what should have been different if it were a collision.

You have a lot invested in the idea that Type 1a SNe are neither usable as standard candles, nor able to be used (by way of width of light curves) as evidence for universal expansion (or against all tired-light models for redshift). As much as I argue against you in these matters, I appreciate your efforts to find holes in the theory, but this is not just cherry picking. I look forward to seeing results concerning similar observations for other seeming type 1a SNe that have excess luminosity.

trinitree88
2007-Nov-02, 06:31 PM
I think the most obvious feature that sets 2006gz apart is that it was brighter, and produced more nickel-56 than the normal type 1a SNe. What this study did was show that there were other observable differences too, and that they matched models for what should have been different if it were a collision.

You have a lot invested in the idea that Type 1a SNe are neither usable as standard candles, nor able to be used (by way of width of light curves) as evidence for universal expansion (or against all tired-light models for redshift). As much as I argue against you in these matters, I appreciate your efforts to find holes in the theory, but this is not just cherry picking. I look forward to seeing results concerning similar observations for other seeming type 1a SNe that have excess luminosity.

Antoniseb. ....I am glad to see that the considerations of a lack of homogeneity of progenitors, considerations of explosion morphological characteristics, and implications of polarimetric viewing are meshing with Sne remnant radio observations and compiled transverse pulsar velocity papers in a coherent scheme on a regular basis in the literature now. It's like watching corn grow....it does happen.... pete.

Fraser
2007-Nov-02, 08:35 PM
I just interviewed one of the researchers on this. I'll publish this as a podcast next week.

Doodler
2007-Nov-02, 08:54 PM
1c is already taken. This type would need a new designation.

Yeah, found that by Wiki right after I posted it, but I'm not one to hide my slip ups.

Would they call this a Type 1d, since its still originating with white dwarves, or a Type III, since it sounds like a very different mechanism than the others?

RUF
2007-Nov-06, 02:14 AM
Could this, in any way, taint the evedince gained from Type 1a's that was used to "discover" dark energy? I seem to remember that descrepencies in 1a's were explained by dark energy. Maybe the actually weren't 1a's but Doodler's "Type 3's"?

Jerry
2007-Nov-06, 03:56 AM
Unfortunately we do not have nearly as much spectrographic and polarmetric detail at high redshifts, where cosmic parameters emerge. Statistically, we should anticipate that the high redshift sample is contaminated with similar events.