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Type Ia Supernovae As Not-Quite-So-Standard Cosmological Candles
Shag writes "Type Ia supernovae are used as cosmological 'standard candles' to measure distance because of their strong similarity to one another. This has made possible, for example, the research into universal expansion that led to the Nobel-winning discovery of 'dark energy.' For years, astrophysicists believed white dwarves exploded when they accreted enough mass from companion stars to reach a limit of 1.38 times the mass of our Sun. A decade ago, the 'Champagne supernova' (SN 2003fg) was so bright astrophysicists concluded the limit had been exceeded by two white dwarves colliding. Now a new paper (PDF) from the Nearby Supernova Factory collaboration suggests that type Ia supernovae occur at a wider range of stellar masses. Fortunately, there appears to be a calculable correlation between mass and light-curve width, so they can still fill the 'standard candle' role, and research based on them is probably still valid. (I took data for the paper, but am not an author.)"
So how far is it to the center of the galaxy this year, given the DOW/NASDAQ are what they Are:)
research based on them is probably still valid
That's probably reassuring.
Better known as 318230.
It's not for us to question it? Learn your bible boy! Just kidding, folks.
Our entire understanding of how the universe works is largly based on these measurements... so this is potentially a very big deal. Any Astrophysicists around that can give us an idea of how big a difference this will make?
Mmm... press release spin.
There is good science here, but it is being heavily spun. The relation between light curve width and how bright SN are has been known since at least 1993 (Phillips, M., 1993, ApJ 413, L105). This was corrected for even in the original work that won the Nobel prize. So, the 'they aren't quite so standard candles' has been known for 20 years - what they are is 'standardizable' candles.
What is interesting about this work is that the SNFactory has tried to find a link between the Phillips relation and physical properties of the explosion - in this case the ejected Nickel 56 mass. And that is very interesting from a SN physics perspective, if not really so much from the 'doing cosmology with Type Ia Supernovae' one.
And to add, this is why people often refer to Ia's as "Standardizable Candles". :)
Talks at Google has a great lecture by Alex Filippenko, called "Dark Energy and the Runaway Universe." There is a wonderful section talking about supernovae as a standard candle from about 17 minutes to 36 minutes, but I recommend the whole thing, as I find it fascinating. http://youtu.be/Guvv5olLxCQ
Most astronomy and astrophysics is best guess under ideal circumstances... Some of the guesses are very good indeed though. Dark energy is just an "x" variable in our mathematical understanding of gravity and space-time. Calling it (dark stuff) a 'discovery' is a bit misleading, as it hasn't actually been, it's only been added as a placeholder! I believe it might be the result of a combination of error terms in the measurements that aren't yet known and a time-geometry, space and time might knot be flat folks.
Hello! I read the same press release, but I don't see the SuperNova Factory taking credit for discovering the relationship between light curve width and luminosity (the Phillips relation, which is indeed well-known, and made the discovery of Dark Energy with Type Ia supernovae possible). So if there is any spin here, it's not on that axis. The press release even acknowledges standardization to about 10% in distance.
Rather, the paper is about explaining this relationship in terms of the underlying physics as you point out. Interestingly, instead of the driver being the amount of radioactive nickel synthesized during the explosion (which is a good candidate for your main lever arm if you believe that total mass of Type Ia progenitors was fixed at/near the Chandrasekhar mass), it is the total mass itself that drives the relationship. It means that the conventional wisdom that the Chandrasekhar mass is somehow important needs another look.
And indeed, this paper *is* interesting also from the "doing cosmology with Type Ia supernovae" perspective. We don't know very well what kinds of white dwarfs and star systems can give us Type Ia supernovae. If there are many different channels, or a continuum of channels, or the distribution of masses of white dwarfs that make Type Ia supernovae somehow evolves with redshift, we need to understand that.
AC1:
The relation between light curve width and how bright SN are has been known since at least 1993 (Phillips, M., 1993, ApJ 413, L105). This was corrected for even in the original work that won the Nobel prize. So, the 'they aren't quite so standard candles' has been known for 20 years - what they are is 'standardizable' candles.
AC2:
I don't see the SuperNova Factory taking credit for discovering the relationship between light curve width and luminosity (the Phillips relation, which is indeed well-known, and made the discovery of Dark Energy with Type Ia supernovae possible).
Well... the Phillips Relationship is "well-known" in much the same way that these supernovae are "nearby" - to the people in that specific very narrow field of expertise. Yes, Wikipedia has an article on it, but I'd expect it to be unknown to the average adult walking down the street, the average amateur astronomer, the average Jeopardy contestant, the average undergraduate or first-year graduate astronomy student, or even the average science popularizer who isn't specifically dealing with supernovae. Just last month, I overheard one long-time amateur astronomer still telling tourists at the Mauna Kea Visitor Information Station that all SNe Ia are the same mass and brightness!
But anyway, as the 2nd AC said, the newer/more interesting bit is the relationship to progenitor mass, and the continued trend toward SNe Ia coming from diverse progenitors - i.e. the more we look, the more "exceptions to the rule" we find. We're already to the point where it looks like most SNe Ia aren't from single, Chandrasekhar-mass progenitors as was long thought to be the "norm," and the paper discusses some models for progenitors of varying masses that meet with varying degrees of success in attempting to match the observational results. I suspect the computational / theoretical / modeling folks will also have fun with it all.
Village idiot in some extremely smart villages.
Okay, strike the last . . . but I can sure come up with more to add. Scientists with the correct equipment and training are going to have to make more observations, propose a hypothesis, test it, fix the details of their theory, test it . . . you know the drill.
(I took data for the paper, but am not an author.)
It's pretty sad when the 35 authors can take paper space acknowledge the culturally significant role that the observatory site has for the indigenous Hawaiians, but can't specifically acknowledge the people who took the data.
The measurement of an acceleration in the expansion of the universe in '98, actually solved a big puzzle for cosmologist trying to match the growth of structure with the cosmological parameters. In hindsight the clues for a universe with dark energy were already there. The combined measurements from the cosmic background radiation, large scale clustering of galaxies, and SNe distances agree on our current model of understanding the universe. Any combination of two of those experiments is enough to constrain the parameters that go into this model. That all three overlap is why we can be confident that the SNe experiment is at the very least reasonably accurate.
- anonymous coward astrophysicist
Hi all, I'm the lead author on the paper who got linked here by a colleague. I agree the Phillips relation is very well-known and well-established *empirically*, and that it is not endangered, nor is my boss going to have to give back his Nobel Prize because we found this out. But understanding this well-known empirical relation theoretically, from first principles, is a real challenge, and it's part of what's preventing us from further improving their performance as "standard candles". We need to continue to refine our understanding of SNe Ia to go to the *next* level in SN Ia cosmology, where we try to figure out what particle or field is responsible for causing the acceleration in the Universe's expansion. So understanding the physics of the supernova explosions is absolutely on the critical path to doing cosmology. The alternative approach is to just accumulate ten million SNe and self-calibrate, which is what LSST is plannign to do. But that will certainly take a lot of time on a half-billion-dollar telescope, to the extent that it's possible without taking spectra of each SN.
There are two main results here. One is the discovery that the ejected mass may be what's driving the Phillips relation, which was suggested before by theorists but never conclusively shown (what about asymmetries? 56Ni mass? weird ejecta density profiles?). The other is simply the fact that a large fraction of normal, non-peculiar SNe Ia may well not be Chandrasekhar-mass, thereby giving us a *lot* of information about how they blew up, and possibly how they evolved to the point of blowing up as well. So it touches on cosmology, but also on stellar evolution, chemical evolution of galaxies, basically every area of astrophysics.
Part of why the Chandrasekhar-mass picture lasted this long is because people didn't think you could standardize non-Chandrasekhar-mass explosions. But you can, and the differences in ejected mass may in fact be what allow us to do that.
(Ah, I see another anon has posted the same thing below. +2!)
Best,
RS
Right from the horse's mouth, folks.
If you claim to know all the answers, then I can safely say that definitely you are NOT a scientist