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I Euclidean differential number counts of supernovae

  1. Nov 26, 2016 #1

    I am working on an assignment which is has asked us to derive an expression for a differential number count of supernovae in a euclidean flat non-expanding space.

    I am bit perplexed by this question and am wondering whether it is a trick question. We are allowed to do research to find an answer outside the text book we have so long as we quote any sources. I have dug around on the net and cant find anything at the moment that seems useful.

    I am stuck because my understanding was/is that supernovae are events rather than 'objects'. I have read somewhere that it is estimate that there is a supernovae once every second in the whole universe. Supernovae only last for a few weeks before they die out, so I dont see exactly how one could count them - at least not in the same way as one might count galaxies or some specific type of star. Since this whole topic is quite new to me, I could be completely wrong and am barking up the wrong tree. Any way, any pointers or suggestions would be greatly welcome. For one thing I am actually still trying to understand properly what a differential number count is. Thanks
  2. jcsd
  3. Nov 26, 2016 #2
    I think you are correct. Supernova is the explosion event where a heavy star is exploding to became a neutron star or a black hole.
    In fact where are at least two types of supernovae. They are distinguished by whether or not a iron core is formed or not, i.e. type I and II. Astrophysicists are also characterizing them in further subgroups.

    However, some types people are speaking of supernovae as objects. But, in that case what is meant is supernova candidates, meaning stars which finally will end their lives in a supernova explosion. I'm not sure but maybe your assignment is to compute this sort of candidates.
  4. Nov 26, 2016 #3
    Check out the intermediate Palomar Transient Factory (iPTF): "a fully-automated, wide-field survey for a systematic exploration of the optical transient sky"

  5. Nov 27, 2016 #4
    Thanks - I was wondering about that also.
  6. Nov 27, 2016 #5
    Thank you . I will check out that link.
  7. Nov 27, 2016 #6


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    This seems to be the most important bit. What is your current understanding of it? Have you ever used it in some other context?

    (for the record, I'm not sure I understand it myself, but maybe we'll come up with something together)

    But there's no essential difference in this regard between a SN and some type of star - both are transient, albeit with vastly different lifetimes. Yet, when you make observations at any given time, you'll observe a specific number of both.
    This is the same as e.g. with observations of dwarf stars and giants - the latter live orders of magnitude shorter than the former, which has the result that at any given time there is more dwarfs than giants to observe (and there's more giants than supernovae).
  8. Nov 27, 2016 #7

    What I have got so far is that in a flat non-expanding space there is a formula of the form: dN/dS is proportional to S^-5/2 Where N is the number of stars and S is the flux of the star. But I have to admit I don't have much of a clue about what it means! I take your point about stars and supernova being the same apart from having different (vastly) lifetimes, and that helps. I will let you know how I get on as I continue to research.
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