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Contact Binary

In Stars by Brian Koberlein3 Comments

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A contact binary star occurs when two stars are close enough that their outer layers are in contact with each other. Often this can occur when one member of a close binary system enters a red giant stage and swells to the point where it is in contact with the companion star. Such systems can create novae, and perhaps supernovae. But recently we’ve discovered a contact binary consisting of two O-type stars.

Currently the two stars orbit each other about once a day, as seen in the artist video above. But their eventual fate is still unknown. Stars of this size typically have a cosmically short lifetime of about 5 million years. It’s possible that they merge into a single, fast-rotating star. Such a supermassive could end its life with a long duration gamma ray burst. But it’s also possible that the stars remain a stable binary throughout their lifetime. If that’s the case, then each would end their lives as supernovae, and produce a black hole. This could create a close black hole binary.

Such a black hole binary would be a boon for astronomers trying to detect gravitational waves, since close binary black holes would create the strongest consistent signal.

Paper: Almeida, L. A., et al. Discovery of the massive overcontact binary VFTS 352: Evidence for enhanced internal mixing. The Astrophysical Journal 812 (2) (2015)


  1. The article does not indicate either the combined or the relative masses of the binary or its constitute stars, although the illustration would seem to indicate that they are least within an order of magnitude of each others mass/size or one would surely already be significantly consuming the other: which was also not indicated. Therefore, would it not be safe to assume that the disruptive potential of either star toward its co-binary to be roughly equivalent so that it matters not which star implodes first??

    This raises in me three or four questions regarding the plausibility of this contact type O binary forming a close black hole binary:

    Would star B survive the supernova of star A or so not be so degraded as to unable to proceed to a back hole producing sized supernova?;

    If so, would the contact or near contact proximity remain–that is neither star is ejected from the system, as we have seen wherein close companion stars have been eject during supernova events (ex. US 708 noted in the Pan-STARRS1 survey results published on, Mar 2015)? And lastly;

    Presuming the answer is yes to both of my first two questions, would not the the now black hole (ex-star A) start consuming star B so rapidly and and so violently as to disrupt the latter through direct consumption and/or tidal disruption, and/or by the intense outward radiation of such a large, rapid and close accretion & consumption process do likewise and prevent star B from proceeding on to a black hole producing supernova because of lost mass and/or severe tidal/physical/mass disruption?

    In the unlikely event that they should both happen to implode at the same time, wouldn’t that be sufficient to eject both of them from the binary?

    1. From the abstract:

      “.. dynamical masses — M1=28.63±0.30M⊙ and M2=28.85±0.30M⊙” . Thus the two blue giants are estimated to be just under 30 solar masses each.

      The system is about 160,000 light years away

  2. but/when/one/explodes/won’t/it/strip/the/other/of/enough/matter/to/preclude/a/blackhole/from/forming?

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