The
football-shaped elliptical galaxy near the center of this image hosted a
surprising supernova last year. PS1-12sk, the yellow dot at image
center, is
classified as a very rare Type Ibn supernova - only the sixth such
example
found out of thousands of supernovae. A Type Ibn supernova is thought to
come from the explosion of a young, massive star. However, the site of
the explosion shows no signs of recent star formation, and a supernova
from a massive star has never before been seen in a galaxy of this type. Credit: CfA / PS1 Science Consortium. Low Resolution Image (jpg)
PS1-12sk, the
yellow dot at image center (circled), is classified as a very rare Type
Ibn supernova - only the sixth such example found out of thousands of
supernovae. It was discovered on the outskirts of a bright elliptical
galaxy (the yellow blob to the upper left of the supernova) located
about 780 million light-years from Earth. A Type Ibn supernova is
thought to come from the explosion of a young, massive star. However,
the site of the explosion shows no signs of recent star formation, and a
supernova from a massive star has never before been seen in a galaxy of
this type. Credit: CfA / PS1 Science Consortium. Low Resolution Image (jpg)
Cambridge, MA - The
star Eta Carinae is ready to blow. 170 years ago, this 100-solar-mass
object belched out several suns' worth of gas in an eruption that made
it the second-brightest star after Sirius. That was just a precursor to
the main event, since it will eventually go supernova.
Supernova explosions of massive stars are common in spiral galaxies like
the Milky Way, where new stars are forming all the time. They are
almost never seen in elliptical galaxies where star formation has nearly
ceased. As a result, astronomers were surprised to find a young-looking
supernova in an old galaxy. Supernova PS1-12sk, discovered with the Pan-STARRS telescope on Haleakala, is rare in more ways than one.
"This supernova is one-of-a-kind," said Nathan Sanders of the
Harvard-Smithsonian Center for Astrophysics (CfA), lead author of the
discovery paper. "And it's definitely in the wrong neighborhood."
Based on the presence of helium and other features, PS1-12sk is
classified as a very rare Type Ibn supernova - only the sixth such
example found out of thousands of supernovae. Although the origin of
this supernova type is unclear, the most likely cause seems to be the
explosion of a massive star that previously ejected massive amounts of
helium gas, much like Eta Carinae's Homunculus Nebula.
That origin was supported by the fact that the five previous Type Ibn
supernovae were all found in galaxies like the Milky Way that are
actively forming stars. (Since massive stars don't live long, they don't
stray far from where they are born before exploding.)
PS1-12sk is different. It was found on the outskirts of a bright
elliptical galaxy located about 780 million light-years from Earth. The
site of the explosion shows no signs of recent star formation, and a
supernova from a massive star has never before been seen in a galaxy of
this type.
"It could be that we simply got very lucky with this discovery. But luck
favors the prepared," said second author Alicia Soderberg of the CfA.
The finding suggests that the host galaxy might be hiding a star
factory, allowing it to form massive stars where none were expected.
Alternatively, PS1-12sk might have an entirely different origin such as a
collision of two white dwarfs, one of which was helium-rich.
"Is this a runaway star from another star formation site? Is it a very
local bit of star formation? Is it a different way for such a supernova
to occur? None of these seems very likely so we have a real puzzle,"
said co-author John Tonry (University of Hawaii Institute for
Astronomy).
The research has been submitted for publication in The Astrophysical Journal.
Headquartered in Cambridge, Mass., the
Harvard-Smithsonian Center for Astrophysics (CfA) is a joint
collaboration between the Smithsonian Astrophysical Observatory and the
Harvard College Observatory. CfA scientists, organized into six research
divisions, study the origin, evolution and ultimate fate of the
universe.
For more information, contact:
David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar@cfa.harvard.edu
Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@cfa.harvard.edu
