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Messier 101 (The Pinwheel Galaxy) and SN 2011 fe (PTF 11kly)

  1. Aug 31, 2011 #1
    In reference to M101 and the Type 1a supernova SN 2011 fe.

    Distances that I have found for M101 vary from 21 million light-years to 28 mly. The value for the measured redshift of M101 is 0.000804. Will the emissions from the supernova create any changes to the redshift measurement? And if so what would be the explanation for the change?
  2. jcsd
  3. Sep 2, 2011 #2
    Since I’m a rank amateur the following may well contain all sorts of errors.

    My understanding is that the importance of SN 2011fe is related to the use of type 1a supernovae as standard candles.

    1a supernovae are very similar to each other since they are thought to occur when white dwarf stars cross (or as some believe, approach to within 1%) the Chandrasekhar Limit (approx. 1.4 times the mass of our Sun).

    To reach this limit matter has to fall onto the white dwarf, probably from a companion star.

    Since the limit is fairly consistent at 1.4 solar masses approximately the same amount of fuel is available for roughly the same type of explosion.

    There is some variation in the size of the explosion (between 1 and 2 times 1044 Joules), but, if I understand correctly, it appears that the absolute brightness of the explosion can be determined fairly accurately from the length of time it takes for the supernova to decay from its brightest to half of its brightest.

    The mechanics are still being worked out, but the differences in brightness are probably mostly determined by the composition of the white dwarf, specifically the mix of Carbon and Oxygen.

    So SN 2011fe should help refine our use of type 1a supernovae as standard candles in several ways.

    First, it gives us the opportunity to study one up close (if you can call 23 Mly “close”). The more we can learn about the dynamics of the explosion the more accurate they will be as standard candles.

    Second, nearby supernovae often give us independent methods of measuring their distance. If we get lucky we may see light echoes as we did for example with SN 1987a. There are other methods, but I’m not sure if they are relevant to type 1a supernovae.

    If we get an independent distance measurement from something like light echoes then that could significantly improve the accuracy of type 1a supernovae as standard candles.

    Since they are near the top of the cosmic distance ladder this means that we may get a re-scaling of almost the entire universe as a result of SN 2011fe.

    I would guess that it could result in a more accurate value for the Hubble constant.

    Returning to your original question, I would not expect an impact on the redshift of M101.

    Of course galactic centres have different red shifts from their outskirts (because galaxies rotate) but with a galaxy as close as M101 I would expect it to be possible to get several values from different objects within the galaxy, including SN 2011fe.

    But since it is so close the redshift is of little value in determining its distance compared to other methods.

    We should get a more accurate distance measurement to M101 as a result of SN 2011fe, especially if the type 1a standard candle method can be combined with something like light echoes.
  4. Sep 17, 2011 #3
    If you could observe the remnants of the SN fromn a vantage point on or near the progenitor star, would you not be looking through a shell of rapidly expanding matter and gasses presenting emission lines, and would this create a redshift of ~12,000kms?
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