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Fraser
2006-Dec-01, 01:51 AM
Type 1a supernovae are used to measure distance in the Universe because they explode with the same brightness, detonating when a white dwarf star consumes a specific amount of material from a binary companion. The accuracy of these distance measurements depends on the shape of the blast. New research indicates that Type 1a supernovae explosions start out clumpy and uneven, but a second, spherical blast overwhelms the first creating a smooth residue. This sets the limits of uncertainty on distance measurements that use Type 1a supernovae.

Read the full blog entry (http://www.universetoday.com/2006/11/30/measuring-the-shape-of-supernove-explosions/)

antoniseb
2006-Dec-01, 12:45 PM
This is good work, and goes well with the SuperMACHO data that shows that the rising side of the SN1a lightcurve can be quite variable, but by the time it reaches peak brightness in the optical spectrum, they are all very close to the same, with the few SN1a-look-alikes being easily identified.

Fraser
2006-Dec-01, 06:38 PM
I found the original press release hard to get a grasp on. I took a long time writing and rewriting my little blurb.

trinitree88
2006-Dec-01, 07:14 PM
[QUOTE=Fraser;875929]Type 1a supernovae are used to measure distance in the Universe because they explode with the same brightness, detonating when a white dwarf star consumes a specific amount of material from a binary companion. The accuracy of these distance measurements depends on the shape of the blast. New research indicates that Type 1a supernovae explosions start out clumpy and uneven, but a second, spherical blast overwhelms the first creating a smooth residue. This sets the limits of uncertainty on distance measurements that use Type 1a supernovae.

Fraser. If that were true, then the further expansion of the blast wave into the interstellar medium ought to yield remnants that are spherical. But close examination of supernova remnants of all types, by M.J.Kesteven and R. N. Manchester in the late 80's, using radio interferometry at the Molonglo Synthesis Radio Telescope, Epping, New South Wales, (Australian Journal of Physics) showed that 48 of 60 old remnants were distinctly barrel-shaped, not spherical, with another 4 possible barrels. That argues distinctly for bipolar emissions and prolate spheroids for most nascent envelopes, not spheres. Again, viewing angle will affect inferred luminosity of these objects. They are only standard candles if they are spherical. With more advanced polarimetric data, determination of the viewing angle may ameliorate the error bars, but it is inherent at this point.
This also holds true for some Cepheid-type variables, the "original" standard candles of the distance scale. (Karovska, Papaliolios, Nissenson..Astrophysical Journal op.cit....Mira, Omicron Ceti...speckle interferometry...asymmetry in the semi-major/ semi-minor axis ratio of ~ 7/5). Seasons greetings. Pete.

GBendt
2006-Dec-01, 11:32 PM
Hi,
The shape of a supernova remnant is not only determined by the symmetry of the supernova explosion (or by the lack of this symmetry), but also by the density of the matter through which the ejected matter travel. The denser this interstellar matter, the more it slows down the momentum of the ejectae. Further, one must consider the effects that twisted and turbulent magnetic fields have on the moving supernova remnant and its shape.

We have no clear information on the correctness of the idea, that every supernova of type Ia produces exactly the same brightness when it explodes.
Further, we do not know whether it shines with the same brightness in any direction, or if the brightness being produced is a different one in different directions. If the latter case turned out to be true, we cannot apply type 1a supernovae as cosmic standard candles any more.
The concept of "dark energy" then might appear to be a wrong conclusion that was taken from misinterpretation of facts.
This would be a desaster for the big bang concept.
We need more precise and carefully checked data on the matter! And leave all those who are in for a sensation out of the process.

Regards,

GŁnther

RussT
2006-Dec-01, 11:57 PM
There is another factor in the mix here that I have never really seen addressed.
Since we 'see' the expansion in the Voids between the clusters, and since those Voids can have very large differnces in size, ie 10 Mpc to 25 Mpc, then it would stand to reason, that the 25 Mpc Voids were expanding More/Faster, then if we are looking at SN1a 'standard candles' across larger Voids in one direction than in another direction, the scope of the expansion would and should be different.

Tensor
2006-Dec-02, 05:13 AM
Hi,

The concept of "dark energy" then might appear to be a wrong conclusion that was taken from misinterpretation of facts.
This would be a desaster for the big bang concept.

Why would you consider this a disaster for the big bang? The one thing the supernova data did, was to show the speed of expanison is increasing. Thus the reasoning for dark energy. If the interpretation of the data is wrong and the speed of expansion is not increasing, all that does is gets the big bang back to not needing dark energy. I'm not quite sure how that is a disaster for the big bang. A disaster for the idea of accelerated expansion, yes, for the idea of the big bang, no.


We need more precise and carefully checked data on the matter! And leave all those who are in for a sensation out of the process.

Since, once the data is published, the data can be checked and rechecked, even by those who don't like the idea, I'm not sure why you would think leaving those who support the idea out would really make a difference.

Jerry
2006-Dec-03, 10:05 PM
Excellent summation, Fraser. And everyone should carefully read Trinitree88's succinct critic, and BBendt obvious questions about fireball size and symmetry. Supernova science has always been based upon iffy assumptions, and more and more data are at odds with the original, optomistic conclusions. In my opinion, not only are the cosmological conclusion scarcely supported, but the Wilson hypothesis as well.

Its is also important to know that preconceptions are limiting the dissemination of plausible alternatives. We have discussed John Middleditch's preprint on several threads, and it remains a preprint because peer reviewers will not recommend it for publication, even after significant changes have been made that address their comments.

One reviewer is a supernova researcher, who used argument similar Antoniseb's on the 'new kind of supernova thread'. This is a good argument for the current theory, but a poor argument against publishing a plausible alternative. The second reviewer stated 'if the Middleditch hypothesis is correct, hundreds of researchers have been wrong'. (This information is from a private communication with John Middleditch.) Hundreds of researchers have been wrong many times - this is never, ever a good reason for rejecting the publication of an alternative theory.

RussT
2006-Dec-04, 01:14 AM
http://www.bbc.co.uk/science/horizon/2001/deathstartrans.shtml

And here is a perfect example of exactly that!

Nearly the entire astronomical community 'shunned' (and other adjectives) Boydan Paczynski for almost 5 years because they were sooooooooooo convinced that they had to be right!!!

I definitely PREDICT that the same thing will happen again, in the not to distant future, that it is determined that GRB's 3 seconds to 500 seconds in duration, ARE NOT EXPLODING/IMPLODING...........STARS!!! There are no SN 1c's!!!!! NO HYPERNOVAE!

John Mendenhall
2006-Dec-04, 04:13 PM
I am amazed that there are so many posts that take an even blacker view of dark matter / dark energy than I do.

So much for the pun. But fellow dm / de detractors, remember, keep an open mind. If the dm / de people are correct, and all they need is a confirmed WIMP, then it takes care of more problems than it creates.