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Old research pages
I'm keeping these old research pages here for the benefit of anyone
who might arrive here from an external page. They are no longer
updated. Please visit my new web site at
http://sipapu.astro.illinois.edu/~ricker/.
Eventually some content from these pages will migrate to the new site.
Type Ia Supernovae
Background
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Whipple Observatory image of the Type Ia supernova
SN 1998bu in M96
(Jha et al. 1999).
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Type Ia supernovae are extremely bright, transient astronomical
sources that most likely result from the sudden release of nuclear
binding energy within a compact stellar remnant such as a white
dwarf (Woosley 1990).
Their peak emission, integrated over all wavebands, typically
exceeds the entire radiative output of their host galaxies, and
their total energy release (typically over a span of days to weeks)
is of order 1051 erg.
Unlike Type II supernovae, their optical spectra do not display
hydrogen lines.
They tend to be found in elliptical galaxies and show no preference
for spiral arms.
These facts suggest that they originate in low-mass stars through
some mechanism other than the core-collapse mechanism generally
thought to produce Type II supernovae.
The best current models attribute them to thermonuclear runaways
in the interiors of white dwarfs of between 0.8 and 1.4 solar masses.
The ignition mechanism is not known.
Deflagration (subsonic, conduction-driven nuclear burning) must
play a role in order to produce the observed intermediate-mass
isotopes, but without a detonation (supersonic, shock-driven burning)
occurring at some point during the event it is difficult to obtain
the observed energy release.
This energy release is easily enough to unbind (disrupt) a white dwarf.
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A progenitor model for a Type Ia supernova.
Matter accreted onto the surface of a white dwarf from its
binary companion causes regions in its interior to become
unstable to thermonuclear runaway.
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Supernovae play a profound role in the history of the universe,
producing the heavier elements without which planets and life would
not exist.
They also serve as excellent beacons, allowing us to measure the distances
to galaxies at high redshift (and thus the expansion rate of the
universe) and to probe the properties of the intervening matter.
However, despite the regularity of the observed properties of Type Ia's
(e.g., the Phillips relation),
we still do not fully understand the physical mechanisms responsible
for them.
The growth of the flame that ultimately becomes the supernova
involves a complex, multidimensional interplay among hydrodynamic
turbulence, diffusive energy transport, a degenerate equation of state,
a network of temperature-sensitive nuclear reactions,
and radiation, occurring over a vast range of length and time scales.
(Diffusive flames wrinkle on the Gibson scale, set by thermal conduction,
nuclear burning, and turbulence at about
10-4 cm; a white dwarf has a radius
of about 108 cm. Nuclear burning occurs on nanosecond timescales,
but produces hydrodynamical effects on timescales closer to 1/10 second.)
Thus analytical models have necessarily been oversimplified, while
numerical models have had to sacrifice three-dimensionality, reaction
complexity, and/or spatio-temporal resolution just to produce results.
References
- Arnett, W. D. Ap&SS 5 280 (1969)
- Arnett, W. D., and Livne, E. ApJ 427 330 (1994)
- Blinnikov, S. I., and Khokhlov, A. M. Soviet Astron. Lett. 12 131 (1986)
- Garcia-Senz, D., and Woosley, S. E. ApJ 454 895 (1995)
- Garcia-Senz, D., Bravo, E., and Woosley, S. E. A&A 349 177 (1999)
- Hillebrandt, W., and Niemeyer, J. C. ARA&A 38 191 (2000)
- Jha, S., et al. ApJS 125 73 (1999)
- Khokhlov, A. M., Oran, E. S., and Wheeler, J. C. ApJ 478 678 (1997)
- Niemeyer, J. C., and Woosley, S. E. ApJ 475 740 (1997)
- Niemeyer, J. C., Hillebrandt, W., and Woosley, S. E. ApJ 471 903 (1996)
- Reinecke, M., Hillebrandt, W., and Niemeyer, J. C. A&A 347 739 (1999)
- Woosley, S. E. in Supernovae, A. G. Petschek, ed. (Springer, 1990)
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