This artist's conception shows the suspected progenitor of a new kind of
supernova called Type Iax. Material from a hot, blue helium star at right is
funneling toward a carbon/oxygen white dwarf star at left, which is embedded
in an accretion disk. In many cases the white dwarf survives the subsequent
explosion.
Credit: Christine Pulliam (CfA). High Resolution Image (jpg) - Low Resolution Image (jpg)
Cambridge, MA - Until now, supernovas came in two main "flavors." A core-collapse supernova is the explosion of a star about 10 to 100 times as massive as our sun, while a Type Ia supernova is the complete disruption of a tiny white dwarf. Today, astronomers are reporting their discovery of a new kind of supernova called Type Iax. This new class is fainter and less energetic than Type Ia. Although both varieties come from exploding white dwarfs, Type Iax supernovas may not completely destroy the white dwarf.
"A Type Iax supernova is essentially a mini supernova," says lead author
Ryan Foley, Clay Fellow at the Harvard-Smithsonian Center for
Astrophysics (CfA). "It's the runt of the supernova litter."
Foley and his colleagues identified 25 examples of the new type of
supernova. None of them appeared in elliptical galaxies, which are
filled with old stars. This suggests that Type Iax supernovas come from
young star systems.
Based on a variety of observational data, the team concluded that a Type
Iax supernova comes from a binary star system containing a white dwarf
and a companion star that has lost its outer hydrogen, leaving it helium
dominated. The white dwarf collects helium from the normal star.
Researchers aren't sure what triggers a Type Iax. It's possible that the
outer helium layer ignites first, sending a shock wave into the white
dwarf. Alternatively, the white dwarf might ignite first due to the
influence of the overlying helium shell.
Either way, it appears that in many cases the white dwarf survives the
explosion, unlike in a Type Ia supernova where the white dwarf is
completely destroyed. "The star will be battered and bruised, but it
might live to see another day," says Foley.
Foley calculates that Type Iax supernovas are about a third as common as
Type Ia supernovas. The reason so few have been detected is that the
faintest are only one-hundredth as bright as a Type Ia.
"Type Iax supernovas aren't rare, they're just faint," explains Foley.
"For more than a thousand years, humans have been observing supernovas.
This whole time, this new class has been hiding in the shadows."
The Large Synoptic Survey Telescope, in which the CfA is a partner, could discover thousands of Type Iax supernovas over its lifetime.
This research has been accepted for publication in The Astrophysical Journal and is available online.
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.
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
