The Contributor to SN 2011fe


When discovered on August 24, 2011, supernova 2011fe was the closest supernova since the famous SN 1987A. Located in the relatively nearby Pinwheel galaxy (M101), it was a prime target for scientists to study since the host galaxy has been well studied and many high resolution images exist from before the explosion, allowing astronomers to search them for information on the star that led to the eruption. But when astronomers, led by Weidong Li, at the University of California, Berkeley searched, what they found defied the typically accepted explanations for supernovae of the same type as 2011fe.

SN 2011fe was a type 1a supernova. This class of supernova is expected to be caused by a white dwarf which accumulates mass contributed by a companion star. The general expectation is that the companion star is a star evolving off the main sequence. As it does, it swells up, and matter spills onto the white dwarf. If this pushes the dwarf’s mass over the limit of 1.4 times the mass of the Sun, the star can no longer support the weight and it undergoes a runaway collapse and rebound, resulting in a supernova.

Fortunately, the swollen up stars, known as red giants, become exceptionally bright due to their large surface area. The eighth brightest star in our own sky, Betelgeuse, is one of these red giants. This high brightness means that these objects are visible from large distances, potentially even in galaxies as distant as the Pinwheel. If so, the astronomers from Berkeley would be able to search archival images and detect the brighter red giant to study the system prior to the explosion.

But when the team searched the images from the Hubble Space Telescope which had snapped pictures through eight different filters, no star was visible at the location of the supernova. This finding follows a quick report from September which announced the same results, but with a much lower threshold for detection. The team followed up by searching images from the Spitzer infrared telescope which also failed to find any source at the proper location.

While this doesn’t rule out the presence of the contributing star, it does place constraints on its properties. The limit on brightness means that the contributor star could not have been a luminous red giant. Instead, the result favors another model of mass donation known as a double-degenerate model

In this scenario, two white dwarfs (both supported by degenerate electrons) orbit one another in a tight orbit. Due to relativistic effects, the system will slowly lose energy and eventually the two stars will become close enough that one will become disrupted enough to spill mass onto the other. If this mass transfer pushes the primary over the 1.4 solar mass limit, it would trigger the same sort of explosion.

This double degenerate model does not exclusively rule out the possibility of red giants contributing to type Ia supernovae, but recently other evidence has revealed missing red giants in other cases.

20 Replies to “The Contributor to SN 2011fe”

  1. Thanks for the interesting web site (as I edit my way out of a poorly thought out question).

  2. You know what, twins are more interesting.

    [Oy vey! How come that every Firefox upgrade UT specifically becomes unstable before the necessary tweaks of FF and plugins are instituted!? This time I found the offending site relatively easy though, so I can start comment.

    However, the page load never finishes, so there are more disrupting stars out there. Seems UT is too complex for standard web browsers.]

    1. It’s more because FF plugins are limited to specific versions of FF, rendering them useless if FF is upgraded… which it happens to do a lot lately. Maybe switch to Chrome?

      1. Good call! And it’s on my agenda to test it. I guess I spend to much time on blogs rather than on my web environment.

      2. Well. I have the newest version of FF and of course running AdBlockPlus (which also canceled those disturbing little pop ups in the lower left corner after I told it to do so). It works nice.

      3. Thanks. I think it is NoScript that messes up. I will try to switch to AdBlock, that is the standby complement for whatever NS doesn’t cope with.

      4. Well, as I said, you have to “right-click” on that pop-up, and then add it to the AdBlock Rules.

        Good luck. 😉

    1. I’ve just stumbled upon the relevant paper (PDF) by the lead astronomer; the dude’s name is Weidong Li, not “Weidon” Li (that’s why I had trouble find it!):
      Exclusion of a luminous red giant as a companion star to the progenitor of supernova SN 2011fe.

  3. Well, that would be quite convenient for it to end up being two small white dwarfs. I hope for the sake of simplicity, it is. Do we have any way of pinning this down? Certainly not by their gravity waves. Just want to go on record as saying since we KNOW we don’t understand everything there is to know about supernovae, I don’t think it’s necessarily a two sided coin were flipping here.

  4. Clearly the relativistic effect which causes the orbital system of the two white dwarfs to lose energy is the emission of gravity waves.


  5. Clearly the relativistic effect which causes the orbital system of the two white dwarfs to lose energy is the emission of gravity waves.


  6. Clearly the relativistic effect which causes the orbital system of the two white dwarfs to lose energy is the emission of gravity waves.


  7. I haven’t read the paper linked (and I probably wouldn’t understand it). Can someone explain why this can’t be:
    1. The companion star lost all its Hydrogen to the SN long ago (it only needs to be 20 years ago to not be visible on old Hubble or Spitzer images)
    2. The companion star is behind enough dust to hide it, but not enough dust to hide the SN


    1. I don’t know about the feasibility of #1, but I believe I can see your general point.

      Sure exceptional cases can happen.

      But these observers would try to fit to the main models first. Both from the viewpoint of likelihood, everything else alike (i.e. no extra data weighing in), and from the viewpoint of trying to make the most of your observations. The latter is both good for them and for science, so it’s a win-win.

  8. What I’d like to know is this: If there are two mechanisms for producing Type Ia SNe, shouldn’t there be some sort of difference in their spectra (in which case we’d have a new category…type Id)?

  9. What about the cloaked stuff? I am but a lamb in the lions den here but, I can imagine a bunch of scenarios like a now extinguished progenitor that dumped enough fuel to bloat a WD to just under the 1.4 limit. The WD now wanders for eons in a dense forest of gas and exotic material slowly accreting until it finally tips the scale? How old can a wandering naked WD get to be and still be a SN candidate? Maybe there’s a bunch of them out there snacking as they wander through the fast food chain.

  10. But… when two neutron stars collide the current assumption is they create a gamma ray burst… doesn’t it?

    1. White dwarfs and neutron stars are different animals altogether.

      The article speaks of a possible white dwarf merger.

      But you are correct that neutron star mergers are expected to produce a GRB.

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