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Supernova Casts Doubt on "Standard Candle"
Krishna Dagli writes, "A supernova more than twice as bright as others of its type has been observed, suggesting it arose from a star that managed to grow more massive than theoretically thought possible. The observation suggests that Type 1a supernovae may not be 'standard candles' — all having the same intrinsic luminosity — as previously thought. This could affect their use as probes of dark energy, the mysterious force causing the expansion of the universe to accelerate."
init 11 - for when you need that edge.
I study supernovae for a living.
i g_tab/nature05103_F1.html
The Nature paper in which this work is published has a figure showing all the measurements of this supernova's brightness; you can see it on Nature's web site at
http://www.nature.com/nature/journal/v443/n7109/f
There are four measurements near time of maximum light, in the red (r) and near-infrared (i) passbands. There are many more measurements starting about 15 days after maximum light in the rest frame, including some in a blue-green (g) passband. Here's what the researchers did to find the maximum brightness of this supernova, so that they could compare it to others:
a) fit models based on the light curves of other supernovae to the r and i measurements,
and the late-time g measurements
b) choose a different passband -- the greenish V passband of the Johnson-Cousins system,
which is closest to their own g passband (the one with no data at max light)
c) use their models to estimate what the light curve in the V filter would have been
This can be a tricky business. Their major conclusion, that this supernova was more luminous than typical ones, is probably correct, but their claim that they can measure the peak magnitude in the V-band to an uncertainty of 6 percent seems a bit bold.
As the press release states, if atypical SNe are very rare, then this probably doesn't have any major impact on the use of Type Ia SNe in cosmology.
Michael Richmond "This is the heart that broke my finger."
mwrsps@rit.edu http://stupendous.rit.edu
It's a pretty familier story, and essential for the advancement of science.
The standard candle was a theory, one that worked well, and now it's in doubt, indicating either that its wrong, or it's incomplete. I'd vote for the latter personally.
That's usually a safe bet...
That's how things move forward.
I shortcut this process. I proved one of my hypothesis wrong even though it had withstood initial tests which indicated correctness. It probably saved a lot of time, but lost me a conference trip, dammit.
Probably not. Gravitational lensing would cause a noticible shift in the star's spectrum.
"...could it be a foreground star and not associated with that galaxy at all?"
Simply put, no.
A light spectrum clearly identifies a supernova for what it is. There is nothing else like it. Also, the redshift in the supernova and surrounding stars gives the distance fairly accurately.