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astronomy Cosmology Physics

Accelerating Universe: Standard ‘light bulbs’ not so standard

I once wrote about one of the problems of determining distance using the so-called standard ‘candle’ of the type Ia supernovae.1  That method is considered to be the gold standard in cosmic distance determination and hence in testing of the expanding universe paradigm. From those measurements, by two independent teams, an accelerating expansion of the Universe was claimed in 1998, for which the Nobel Prize in Physics was awarded in 2011.

That same galaxy in a NASA Swift image is shown, with bars indicating the location of supernova SN 2011fe. The Swift image is a false-color image with UV emission blue and optical emission red. Credit: NASA/Swift
An optical image of the galaxy M101, with bars indicating the location of supernova SN 2011fe. This NASA/Swift image is a false-color image with UV emission shown in blue and optical emission shown in red. Credit: NASA/Swift

Type Ia supernova were (are) believed to be a class of stellar explosions that resulted from progenitor stars with a very small range of masses and chemical properties. It was (is) believed that these could be accurately modelled and therefore they could be relied upon to produce the same intrinsic brightness in their explosions. It was believed therefore that they varied only by a very small degree in a distribution around a well established intrinsic brightness or absolute magnitude near MB ~ -19. That means they were believed to all have the same intrinsic brightness.