By this March, nearly two years after the supernova first appeared in the Whirlpool Galaxy, Van Dyk and his colleagues commandeered Hubble once more to take another look. To their surprise, the yellow supergiant star, which they had presumed to be a mere bystander to the explosion, had vanished. Another team, using telescopes on the ground, saw the same thing. “We just wanted to see what the evolution of the supernova was,” Van Dyk says. “We fully expected the yellow supergiant to still be there in these images this year.”
The supergiant’s disappearance implicated the star as the source of the supernova after all. Van Dyk and his colleagues published their findings, which validated the conclusions of their competitors, in the August 1 issue of The Astrophysical Journal Letters. “The other team was actually correct, and we were fully contrite in that way,” Van Dyk says.
But the saga of supernova 2011dh will not end there. As the bright blemish of the supernova remnant continues to fade, the Whirlpool will return to its pre-2011 appearance—minus one supergiant star. Toward the end of the year, as early as mid-November, the supernova’s glow will have faded so much that the yellow supergiant’s surviving partner should come into view—if indeed the star was locked in a binary pairing as has been invoked to explain the rare type IIb event. “You should actually be able to see the companion star in the binary system,” Van Dyk says, noting that multiple teams have secured time on the Hubble telescope to follow the evolution of supernova 2011dh. “If they see the binary companion, then that lends a lot of credence to this binary pathway to this type of supernova,” he adds. “And that would be really important.”