11.8 Type Ia Supernovae

If a white dwarf accumulates matter from a companion star at a much faster rate, it can be pushed over the Chandrasekhar limit. The evolution of such a binary system is shown in Figure 11.18. When its mass approaches the Chandrasekhar mass limit (exceeds 1.4 MSun), such an object can no longer support itself as a white dwarf, and it begins to contract. As it does so, it heats up, and new nuclear reactions can begin in the degenerate core. The star “simmers” for the next century or so, building up internal temperature. This simmering phase ends in less than a second, when an enormous amount of fusion (especially of carbon) takes place all at once, resulting in an explosion. The fusion energy produced during the final explosion is so great that it completely destroys the white dwarf. Gases are blown out into space at velocities of about 10,000 kilometres per second, and afterward, no trace of the white dwarf remains.

Evolution of a Binary System

Illustration of the Evolution of a Binary System. From left to right the “Primary star” is at bottom drawn as a large white circle. The “Secondary star” is at top as a smaller white circle. A grey arrow points to the right to the next phase. The primary has evolved into a “Red giant”, drawn as a large red circle, and the secondary remains a “Main-sequence star”. A grey arrow points to the right to the next phase. The primary has evolved into a “White dwarf”, drawn as a white dot, and the secondary remains a “Main-sequence star”. A grey arrow points to the right to the next phase. The primary remains a “White dwarf” while the secondary has evolved a “Red giant”, drawn as a large red circle with material flowing toward the white dwarf. A grey arrow points to the right to the final phase. The primary has exploded as a “Type Ia supernova”, drawn as a white blob with debris streaming outward, and the secondary has evolved into a “Red-giant remnant”.
Figure 11.18. The more massive star evolves first to become a red giant and then a white dwarf. The white dwarf then begins to attract material from its companion, which in turn evolves to become a red giant. Eventually, the white dwarf acquires so much mass that it is pushed over the Chandrasekhar limit and becomes a type Ia supernova.

Such an explosion is also called a supernova, since, like the destruction of a high-mass star, it produces a huge amount of energy in a very short time. However, unlike the explosion of a high-mass star, which can leave behind a neutron star or black hole remnant, the white dwarf is completely destroyed in the process, leaving behind no remnant. We call these white dwarf explosions type Ia supernovae.

Attribution

“23.5 The Evolution of Binary Star Systems” from Douglas College Astronomy 1105 by Douglas College Department of Physics and Astronomy, is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted. Adapted from Astronomy 2e.

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Fanshawe College Astronomy Copyright © 2023 by Dr. Iftekhar Haque is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.