Difference between revisions of "Supernova"
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==Type I== | ==Type I== | ||
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| + | ===Type 1a=== | ||
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| + | Although the exact mechanism that causes type I supernovae is still not entirely understood, for type Ia supernovae, it is generally accepted to occur most often in binary star systems where one of the binary stars is a white dwarf (typically a [[carbon]]-[[oxygen]] dwarf) that is drawing mass from its high mass companion. As the mass from from the companion accumulates on the surface of the [[white dwarf]] it compresses and heats up. Often, the hydrogen in the accumulated mass will heat enough to initiate hydrogen fusion, causing a [[nova]]. If however the white dwarf accumulated enough matter from its companion to have a mass that reaches its [[Chandrasekhar limit]], the white dwarf will no longer be able to support itself via electron degeneracy pressure against the increase in [[gravity]] from the additional mass.<ref>http://adsabs.harvard.edu/abs/1987ApJ...323..140L</ref> A significant portion of the white dwarf will then undergo nuclear fusion within seconds, releasing enough energy to cause the star to explode as a supernova.<ref>http://www.sciencemag.org/cgi/content/abstract/315/5813/825</ref> | ||
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| + | Type Ia supernovae are important to [[astronomy]] because they act as standard candles for measuring extra-galactic distances, especially pertaining to other galaxies. This is due to such supernovae explosions having the same luminosity, an absolute magnitude of -19.3 (some five billion times the sun's brightness). The source of this brightness is the generated by radioactive decay of nickel-56. The [[nickel]]-56 is formed during the explosion event itself and decays through [[cobalt]]-56 to [[iron]]-56.<ref>http://adsabs.harvard.edu/abs/2000ARA&A..38..191H</ref>. | ||
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| + | In 1998, observations of the apparent magnitude of several type 1a supernovae in other galaxies, resulted in the surprising finding that the universe is expanding at an accelerated rate, due to [[Dark energy|Dark Energy]].<ref>http://arxiv.org/abs/astro-ph/9805201</ref> | ||
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| + | ===Type 1b and Ic=== | ||
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| + | Type lb and Ic supernovae, like Type II supernovae, are from massive stars that are running out of core fuel for fusion. However the stars for type Ib explosions had their outer shell of hydrogen lost or striped away, and type Ic are from stars that have lost most of both its [[hydrogen]] and subsequent [[helium]] shell. This loss is either due to intense stellar winds, or from interaction with a nearby binary companion of sufficient mass.<ref>http://adsabs.harvard.edu/abs/1997rdbs.conf..153P</ref> It is believed that type 1b supernovae are from exploding [[Wolf-Rayet]] stars. There is some evidence that a small percentage of type Ic supernovae are the source of [[Gamma-Ray Bursts|Gamma Ray Bursts]].<ref>http://adsabs.harvard.edu/abs/2004MNRAS.349.1093R</ref> | ||
==Type II== | ==Type II== | ||
Revision as of 20:27, October 25, 2009
A supernova is a large stellar explosion that releases a tremendous amount of energy and destroys the star in which it originated. There are two types of supernovas, called, easily enough, type I and type II
Type I
Type 1a
Although the exact mechanism that causes type I supernovae is still not entirely understood, for type Ia supernovae, it is generally accepted to occur most often in binary star systems where one of the binary stars is a white dwarf (typically a carbon-oxygen dwarf) that is drawing mass from its high mass companion. As the mass from from the companion accumulates on the surface of the white dwarf it compresses and heats up. Often, the hydrogen in the accumulated mass will heat enough to initiate hydrogen fusion, causing a nova. If however the white dwarf accumulated enough matter from its companion to have a mass that reaches its Chandrasekhar limit, the white dwarf will no longer be able to support itself via electron degeneracy pressure against the increase in gravity from the additional mass.[1] A significant portion of the white dwarf will then undergo nuclear fusion within seconds, releasing enough energy to cause the star to explode as a supernova.[2]
Type Ia supernovae are important to astronomy because they act as standard candles for measuring extra-galactic distances, especially pertaining to other galaxies. This is due to such supernovae explosions having the same luminosity, an absolute magnitude of -19.3 (some five billion times the sun's brightness). The source of this brightness is the generated by radioactive decay of nickel-56. The nickel-56 is formed during the explosion event itself and decays through cobalt-56 to iron-56.[3].
In 1998, observations of the apparent magnitude of several type 1a supernovae in other galaxies, resulted in the surprising finding that the universe is expanding at an accelerated rate, due to Dark Energy.[4]
Type 1b and Ic
Type lb and Ic supernovae, like Type II supernovae, are from massive stars that are running out of core fuel for fusion. However the stars for type Ib explosions had their outer shell of hydrogen lost or striped away, and type Ic are from stars that have lost most of both its hydrogen and subsequent helium shell. This loss is either due to intense stellar winds, or from interaction with a nearby binary companion of sufficient mass.[5] It is believed that type 1b supernovae are from exploding Wolf-Rayet stars. There is some evidence that a small percentage of type Ic supernovae are the source of Gamma Ray Bursts.[6]
Type II
A type II supernova is a stellar explosion involving a star at the end of its life, when its nuclear fuel is exhausted and it is no longer supported by the release of nuclear energy. This is one of the most powerful events in the universe. It often causes stars that are not normally visible to the naked eye to become apparent in the night sky due to the extreme amount of light given off in the explosion. If the star is particularly massive, then its core will collapse and in so doing will release a huge amount of energy. This will cause a blast wave that ejects the star's envelope into interstellar space. The result of the collapse may be, in some cases, a rapidly rotating neutron star that can be observed many years later as a radio pulsar.
Observed Supernovas
While many supernovae have been seen in nearby galaxies, they are relatively rare events in our own galaxy. The last to be seen was Kepler's star in 1604. This remnant has been studied by many X-ray astronomy satellites, including ROSAT. There are, however, many remnants of supernova explosions in our galaxy, that are seen as X-ray shell like structures caused by the shock wave propagating out into the interstellar medium. Another famous remnant was observed in 1054, when Chinese astronomers recorded a supernova so bright that it was visible during the day. This supernova is believed to be the one reported by Marco Polo. The explosion left behind a pulsar and a huge cloud of gas and dust known as the Crab Nebula, which still can be seen today with its pulsar rotating 30 times a second and emitting X-rays in a fashion similar to a lighthouse. [1].
External links
- ↑ http://adsabs.harvard.edu/abs/1987ApJ...323..140L
- ↑ http://www.sciencemag.org/cgi/content/abstract/315/5813/825
- ↑ http://adsabs.harvard.edu/abs/2000ARA&A..38..191H
- ↑ http://arxiv.org/abs/astro-ph/9805201
- ↑ http://adsabs.harvard.edu/abs/1997rdbs.conf..153P
- ↑ http://adsabs.harvard.edu/abs/2004MNRAS.349.1093R