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Fig. 1:
Snapshots of the merger of two equal size white dwarf stars from 36 seconds
prior to the explosion until 10 seconds afterwards. The colour-coding
indicates the density of material, which is increasing from blue to red.
Please note the different scaling on the plots.
(Image: Max Planck Institute for Astrophysics)
 Movie: Computer simulation of two merging white dwarfs (MPEG1 Format)
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Intermediate-mass stars such as our Sun end their lives as white dwarfs
consisting of carbon and oxygen. The stellar fusion reactor in their centre
is no longer active due to a lack of fuel. The stars have only the size of
the Earth, but a high density. One teaspoon of matter would weigh about as
much as a car on our planet.
In a binary system, two such exotic white dwarfs can form. As they orbit
each other, they are emitting gravitational waves. The resulting energy
loss shrinks the orbit, the stars approach each other and ultimately they
merge. It has long been speculated that these events may produce Type Ia
supernova explosions.
The supernova research group at the Max Planck Institute for Astrophysics
has now performed computer simulations of two merging white dwarfs in
unprecedented detail. In the case of equal masses of the two white dwarfs,
the merger is particularly violent. Part of the material of one white dwarf
crashes into the other and heats up the carbon/oxygen material such that a
thermonuclear explosion triggers (see Figure). This disrupts the stars in a
supernova explosion.
"With our detailed explosion simulations, we could predict observables that
indeed closely match actual observations of Type Ia supernovae," explains
Friedrich Röpke of the supernova team. Therefore it has been demonstrated
that white dwarf mergers contribute to Type Ia supernovae, although this
scenario probably cannot account for all these explosions.
"Supernovae are among the brightest observed cosmic explosions," explains
Wolfgang Hillebrandt, director at the Max Planck Institute for Astrophysics
and co-author of the Nature article. "How they form, however, remains
largely unknown. With our simulations we have now shed light on at least
part of the old riddle of the progenitors of Type Ia supernovae."
Original publication:
Rüdiger Pakmor, Markus Kromer, Friedrich K. Röpke, Stuart A.Sim, Ashley
J. Ruiter, Wolfgang Hillebrandt,
"Sub-luminous type Ia supernovae from the mergers of equal-mass white dwarfs
with M~0.9 M_solar",
Nature, 7. January 2010
Links:
Website of the supernova research group
Computer simulation of two merging white dwarfs (
MPEG4 Format ,
MPEG1 Format )
Contact:
Dr. Hannelore Hämmerle
Press Officer
Max Planck Institute for Astrophysics
and Max Planck Institute for extraterrestrial Physics
Phone: +49 89 30000-3980
E-Mail: hhaemmerle mpa-garching.mpg.de
Prof. Wolfgang Hillebrandt
Max Planck Institute for Astrophysics
Phone: +49 89 30000-2200
E-mail: whillebrandtmpa-garching.mpg.de
Dr. Friedrich K. Röpke
Max Planck Institute for Astrophysics
Phone: +49 89 30000-2212
E-mail: froepkempa-garching.mpg.de
Rüdiger Pakmor
Max Planck Institute for Astrophysics
Phone: +49 89 30000-2271
E-mail: rpakmormpa-garching.mpg.de
Acknowledgement:
We thank Elena Erastova and Markus Rampp (Max-Planck-Rechenzentrum Garching)
for the movie. The use of the Splotch visualization package by K. Dolag, M.
Reinecke, C. Gheller and S. Imboden is acknowledged.
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