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."

Comments

Re:Canada-France-Hawaii telescope?

[Silver Sloth]

because

CFHT is a joint facility of:

* National Research Council of Canada (see also Herzberg Institute of Astrophysics),
* Centre National de la Recherche Scientifique of France (see also CNRS/INSU ), and
* University of Hawaii (see also UH/IfA ).

i.e. two national bodies and one local body. This is all on their website http://www.cfht.hawaii.edu/

The observational evidence is surprisingly scanty

[StupendousMan]

I study supernovae for a living.

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/fi g_tab/nature05103_F1.html

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.