Hubble observes Supernova explosion of Yellow Supergiant

M51 Galaxy before (left) and after (right) the eruption of SN 2011dh. 

The image on the left was taken in 2009, and on the right on July 8th, 2011. 

Credit: Conrad Jung.

Observational results of the Hubble Space Telescope announced in March 2013 confirmed the theoretical prediction by the Bersten team at the Kavli Institute for the Physics and Mathematics of the Universe that the yellow supergiant star found at the location of supernova SN 2011dh in the famous nearby galaxy M51 was indeed the star that exploded.

The nature of the progenitor star (or progenitor system) of core-collapse supernovae and the origin of their diversity are important open questions in the field of astrophysics.

It has been believed that most massive stars explode when they become red supergiants, or, alternatively, blue compact stars (Wolf-Rayet stars).

The supernova SN 2011dh that appeared in the M51 galaxy revealed a different story.

Two groups of astronomers independently detected a yellow supergiant (YSG) star at a location closely matching that of the supernova in archival images obtained with the Hubble Space Telescope (HST) before the supernova explosion.

A question then arose as to how such a star could undergo a supernova explosion. The YSG phase is an intermediate, short-lived stage in the evolutionary models of single stars, during which no supernova explosions are expected to occur.

With the explosion of the YSG star confirmed, there is one last piece of the puzzle that still needs to be proved: the existence of the companion star predicted by the binary model.

According to the calculations, at the moment of the supernova explosion, the companion should be a massive, blue star.

Because of its high surface temperature, this star should emit mostly in the ultraviolet range, with a negligible contribution to the total flux of the system in the optical range.

The companion was faint enough not to be detected in the pre-supernova images of the space telescope but in the near future, as the supernova continues to fade, the relatively faint companion star can be recovered.

A team at the Kavli IPMU (Folattelli et al.) has thus proposed to perform deep observations with the HST and the Keck & Subaru telescope in 2014 to provide a definitive test for the validity of their models.

Reference:
"The Type IIb Supernova 2011dh from a Supergiant Progenitor," Melina C. Bersten, Omar G. Benvenuto, Ken'ichi Nomoto et al. 2012 ApJ 757 31 doi:10.1088/0004-637X/757/1/31