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I Hubble finds universe may be expanding faster than expected

  1. Jun 2, 2016 #1
    According to the paper they used 300 SNe Ia along with Cepheid variables, as a basis for determining cosmological distances. With the exception of 19 SNe Ia, which were calibrated using nearby Cepheids, the remaining 281 SNe Ia were based purely on their light curve to determine their type. There is a fundamental problem with this methodology, when it is the only basis used to determine the type of a SNe. It is not always accurate. SNe Iax have the exact same light curve, including the lack of hydrogen in its spectrum as SNe Ia, except that they are several orders of magnitude dimmer than SNe Ia.

    All SNe Ia have an absolute magnitude of -19.3, which is why they are used as a "standard candle." However, unless one also looks at other factors, such as the velocity of the ejecta, you cannot rule out the possibility of a SNe Iax, which could have an absolute magnitude anywhere from -14.2 to -18.9. All SNe Ia have ejecta with velocities that equal or exceed 10,000 km/s, whereas all SNe Iax ejecta velocities are less than 8,000 km/s. But if you only look at the light curve of the SNe, then there is no way to be certain if it is actually a SNe Ia. It is estimated that anywhere from 18% to 48% of all the SNe Ia have been misclassified and should actually be the much dimmer SNe Iax. That is a significant margin for error, and would have a profound effect determining the rate of expansion.

    Sources:
    A 2.4% Determination of the Local Value of the Hubble Constant - arXiv 1604.01424
    Type Iax Supernovae: A New Class of Stellar Explosion - The Astrophysical Journal, Volume 767, Number 1, March 25, 2013 (free issue)
     
    Last edited: Jun 3, 2016
  2. jcsd
  3. Jun 3, 2016 #2
    I was about to post about this here in the forum, but you beat me to it, Glitch! :smile:
     
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