From: eric@flesch.org (Eric Flesch) Subject: Supernova Double Fireball KO's Cosmological Time Dilation Date: 1997/12/07 Message-ID: <34966bb0.50666189@news.nn.iconz.co.nz> Organization: Internet Company of New Zealand Newsgroups: sci.physics,sci.astro Cosmological time dilation is the single most definitive key test between the Big-Bang and Steady-State models of the universe. We know that galaxies at about 10^10 LY are redshifted by 50% (z=1), but does the redshift betoken a 50% time slowage, or is some other physical artifact at work? If it were to be determined that there is *no* cosmological time dilation, the Big Bang theory would be cashiered instantly, as such dilation is an *essential* part of the theory. Similarly, it is hard to envision a Steady State theory that could accomodate cosmological time dilation, as if there is currently a precise 10^10 year time lag between us and a galaxy at z=1, then tomorrow there would be a 10^10 year + 12 hour time lag. How could a steady-state universe accomodate such a changing yardstick and still be steady-state? It's been an urban legend since 1995 that cosmological time dilation has been demonstrated to be true. Prior to 1995 the only attempt at finding cosmological time dilation was with gamma-ray burst profiles, but such analysis is speculative and the profiles can simply be modelled with a burst luminosity function. In 1995 Goldhaber et al presented the first results of analysis of the light curves of type Ia supernovae at various distances to z=0.4. These results were publicized as the first demonstration of cosmological time dilation, and this belief remains to this day. However, subsequent events, not so well publicized, have derailed those early efforts. The method used was that of fitting observed light curves against a supernova lightcurve template called the "Leibundgut SN Ia template" which was compiled by Bruno Leibundgut in 1991 as a typical curve for the believed-to-be-homogeneous type Ia supernova. Leibundgut considered his template to be reliable except during the days of increasing flux (i.e. from detonation to 5 days before maximum), as the data is sketchy for those times. Goldhaber's team however used the template over the entire supernova history. A potential systematic error was thus introduced, if the template's lightcurve from detonation to maximum was wrong. This year Leibundgut himself and W. Vacca have published "Modelling the Lightcurves of Type Ia Supernovae" for the NATO Advanced Study Institute on Thermonuclear Supernovae. This paper re-examines the fundamentals behind the Leibundgut templates. It turns out that the previously-believed-to-be consistent type Ia supernova have *two* explosive detonations in their history, not one, and this rewrites the curves of the Leibundgut template. I would like to share the insights, method, and commentary in this paper with you. The paper starts by acknowledging the current belief that there is "a substantial degree of homogeneity among the members of this SN subclass", that is, among supernovae (SN) of Type Ia. It continues, "However, as more and better data on Type Ia SNe have become available... it has become clear that ... the lightcurves of SN Ia are *not* (emphasis paper's) identical and some supernovae have displayed pronounced deviations from the means represented by the templates." This paper boldly presents the latest observational data without recourse to any theoretical model. The authors comment, "While not based on any particular physical model, this purely empirical form accounts for the various phases of SNe I lightcurves and provides a continuous representation of the data". (As a side note, I wish more researchers would boldly present their results without regard to theory. E.g., imagine: "We measure a Hubble constant of 93. Theory be damned!".) :-) Vacca and Leibundgut present the photometric U, B, V, R, & I lightcurves of the well-observed SN Ia 1994D on pages 5 & 6. These curves do not look like the earlier Leibundgut templates! This SN brightened enormously over about a week, took about 12 days to brighten the final 2 magnitudes to maximum, then declined about 3 magnitudes before hitting an inflection point where the flux fall-off suddenly becomes more gradual. The curve looks like a black-body emission curve before this inflection, and indeed Vacca and Leibundgut comment that the color & spectrum resembles a black body too, but after the inflection the spectrum is dominated by emission lines. The I (infrared) bolometric lightcurve shows a distinct secondary maximum flux of the supernova. Basically there have been two explosions, the first producing a fireball which initially expands faster than it fades, so that maximum brightness is reached about 2 weeks after the explosion. This initial expanding fireball is overtaken about 20 days later by a second shock wave which increases the expansion rate of the visible shell. This increased expansion accounts for the slowing of the brightness decrease. This physical interpretation is my own, but seems a straightforward accounting for this bolometric luminosity lightcurve. Vacca and Leibundgut compare this well-recorded SN 1994D with other supernovae and find that the evidence of the secondary increase is generally present. Basically, the Type Ia Supernova suffers not one explosion but two, and the shock wave from the second explosion catches and passes the first after about 40 days. Thus does our knowledge of supernova increase with observation, and previous theory will just have to be revised to accomodate the new observational realities. Thus has it ever been, thus shall it ever be. Of course we now have two significant differences in the lightcurve template from the old Leibundgut model. The ascension to the maximum is sharper to begin with (28 magnitudes in 6 days) and then gradual (2 magnitudes in 12 days), and the luminosity decline suffers an inflection point at about 40 days (or even a luminosity increase), thus stretching out the decline profile compared with the time of maximum. This extra stretch bodes ominous for the Leibundgut-template fits done by Goldhaber et al in 1995, when they declared the observed stretch to be convincing evidence for cosmological time dilation. Sorry fellas. Try this new template instead, eh? The integrity of the authors' (William Vacca and Bruno Leibundgut) methodology in their paper emanates from every sentence. Their only concern is that the information should be right. Leibundgut does not care if his previous works and templates are superseded or even proved wrong, he only wants the correct model to come out, the truth to be revealed. Vacca and Leibundgut are researchers of the first order. Now, it's not really true that cosmological time dilation has been KO'd by the latest developments in SN Type Ia research. I took some literary license in the title. Cosmological time dilation may still be true, and Perlmutter et al have an article about a z=.83 SN in the journal "Nature" due out on New Year's day. But the current status is that cosmological time dilation has not been demonstrated at all. The work has yet to be done. Until it is properly demonstrated, to your, mine, and Leibundgut's satisfaction, it isn't proven. So it *might* yet be proven wrong. Put this item back on your "unknown" shelf, and stay tuned. Eric Flesch