A Supergiant Star Goes Missing, and a Supernova Mystery Is Solved

A Supergiant Star Goes Missing, and a Supernova Mystery Is Solved
http://www.scientificamerican.com/ar...vanishing-star

So it was with a recent supernova in the spiral galaxy M51—better
known to casual stargazers as the Whirlpool galaxy, a photogenic
swirl some 25 million light-years away. Shortly after the light from
an exploding star there reached Earth at the end of May 2011, amateur
reports of the cataclysm began pouring in to the Central Bureau for
Astronomical Telegrams, a clearinghouse for new telescope data. Soon
the explosion was assigned the official designation supernova
2011dh.

The Whirlpool galaxy has plenty of admirers, so a brand-new bright
spot on the edge of the spiral was sure to catch the attention of
many observers. “It’s really one of the nearest galaxies, and it’s a
galaxy that’s beautiful and very famous,” says astronomer Schuyler
Van Dyk of the California Institute of Technology.



Astronomers have some general explanations for type IIb explosions,
but uncovering the exact chain of events leading up to a supernova is
a difficult task. Because astronomers never know that a star is about
to go supernova until it has already exploded, it is usually
impossible to determine which star, exactly, met its violent end.
Only in rare cases can astronomers turn up sufficiently detailed
pre-explosion images of the region in question to identify the
culprit. In 2011, however, the famousness of the Whirlpool galaxy
once again came in handy. “Within days of discovery of the supernova
we went to the Hubble Space Telescope data archive, and it turned out
that one of the former directors of the HST had orchestrated this
beautiful mosaic of M51—this glorious picture in various colors,” Van
Dyk says. In the Hubble images, at the very spot where the supernova
appeared without warning in 2011, there had been in 2005 an
unremarkable yellow supergiant star.