The progenitor star that produced the May supernovae in the Whirlpool Galaxy (also known as M51) has been identified, and it isn’t what scientists predicted.
In a preprint paper published today on the Los Alamos astro-ph website, astronomers describe the star that exploded as a yellow supergiant, not a red supergiant or Wolf-Rayet star, as predicted by the theory explaining this particular type of supernova. Moreover, though theory also favors the star being a member of a binary system, the progenitor of 2011dh appears to be a lone star, not even a member of a cluster.
Before it exploded, the star is believed to have been an F-type supergiant with an effective surface temperature of approximately 6000 degrees Kelvin and a core mass of about 13 solar masses. The spectroscopy suggests that the star had already lost most of its hydrogen envelope prior to the eruption, and was burning its helium core.
This new data point only adds to the growing database of supernovae progenitors that is increasingly baffling the theorists, as the mix of properties and types of these stars is not matching their theories. As noted in the paper’s conclusion:
Despite the canonical prediction that Type II supernovae arise from red supergiants, there is mounting evidence that some stars explode as yellow supergiants. A handful of Type II supernovae have been observed to arise from yellow supergiants: SNe 1993J and 2009kr. The locations of the progenitors on the Hertzsprung-Russell diagram shows clearly that these stars are not located on the predicted end points for single star stellar evolution tracks. In addition, despite arising from supposedly similar yellow supergiant progenitors, these supernovae display a wide range of properties.
Not surprising, nature is once again throwing us a curveball. The kinds of supernovae and the stars that produce them is turning out to be far more complicated than the theorists had predicted. And without a solution to this mystery, it will be impossible for scientists to identify which stars in our galaxy will be the next to go boom.
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