Supernovae
Supernovae are massive giant exploding stars. When the explosion occurs, the resulting illumination can be as bright as an entire galaxy! Supernova occurs at the end of a star's lifetime, when its nuclear fuel is exhausted and it is no longer supported by the release of nuclear energy. 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.
As a result of gravitational forces acting against the nuclear structure of the core of a fuel depleted star, tremendous shock waves are generated which cause the outside layers of the star to be blown away from the core.
One type of Supernova involves two stars, one of them being a white dwarf whose gravitational attraction is so intense that it is capable of siphoning off material from its companion. Unfortunately for the star (but fortunately for us at a long distance!), the white dwarf exceeds its Chandrasekhar limit of stability causing it to go into thermonuclear instability and produces one of the largest explosions known in the Universe.
Another type of supernova involves a collapse of the core of a fuel depleted star, tremendous shock waves are generated which cause the outside layers of the star to be blown away from the core. Gravitational forces condensing hydrogen gas raises the temperature at the center of the star to the point where nuclear fusion is initiated. Hydrogen is fused into helium and energy is given off in the process. As more helium accumulates at the center, the temperature rises due to compression until another nuclear fusion is initiated. This time helium is converted to carbon and oxygen and additional energy is given off during the nuclear fusion.
A similar process continues with carbon and oxygen fusing to neon, magnesium, and oxygen. These elements then undergo another fusion process as the temperature and pressure increase to produce silicon and sulfur. The latter two elements then fuse into iron. During each nuclear fusion, energy is given off. This takes two orders of magnitude less time to happen than on the previous fusion. However, nuclear fusion stops at iron because energy is no longer produced by fusion. The iron core collapses very quickly (within hours or less).
Since the iron core can collapse only so far and can no longer undergo fusion, it becomes extremely hot and now begins to expand rapidly. This occurs while the star's outer shells are rushing in to fill the void left by the collapsed iron core. The expanding iron and the collapsing outer gases collide with each other producing tremendous shock waves which blow the outer layers away from the core, thus causing the supernova's gigantic explosion.
What happens after the explosion depends on the type and mass of the progenitor stars. Mostly they produce a gas cloud called a supernova remnant which initially expands at a rate of about 10,000 km/s. Gradually the expansion rate slows down while dissipating into the interstellar medium, seeding the neighborhood with heavy elements and providing the necessary shock waves for new stellar formation.
New Type of Supernova Discovered National Geographic - November 6, 2009
Rapid supernova could be new class of exploding star PhysOrg - November 5, 2009
11-Billion-Year-Old Giant Supernovae Farthest Ever Detected PhysOrg - July 8, 2009
Most Distant Supernovae Found National Geographic - July 8, 2009
First 3-D Fly-Through of a Supernova Remnant National Geographic - January 7, 2009
Ancient supernova mystery solved BBC - December 4, 2008
Supernova "Shock Breakout" Seen From Red Giant For The First Time National Geographic - June 12, 2008
"Light Echo" Helps Solve Supernova Mystery National Geographic - May 29, 2008
Astronomers have used an interstellar "mirror" to solve the longstanding mystery over what kind of supernova created Cassiopeia A, one of the brightest radio objects in the sky. Cass A, as the object is often called, is the expanding remains of a stellar explosion about 9,000 light-years away that is believed to have occurred around A.D. 1680. Until now no one has been able to pinpoint the exact nature of the blast.
Supernova Caught Starting to Explode for First Time National Geographic - May 21, 2008
Brightest Known Supernova Detected National Geographic - October 15, 2007
Enigmatic supernova smashes brightness record New Scientist - October 12, 2007
Supernova blazed like 100 billion suns MSNBC - October 12, 2007
The Brightest Supernova Ever NASA - May 7, 2007
Astrophysicists Explain Differences In Brightness Of Supernova Explosions Science Daily - February 23, 2007
Brightest supernova discovery hints at stellar collision New Scientist - January 4, 2007
Supernova captured in 'real time' BBC - August 30, 2006
Mystery object found in supernova's heart Space.com - July 7, 2006
... energetic X-ray emissions of the blue point-like object cycles every 6.7 hours
tens of thousands of times longer than expected for a freshly created neutron star
Native Americans may have recorded supernova explosion in 1006 AD Space.com - June 6, 2006
Supernova shock wave creates halo effect New Scientist - August 19, 2005
The shock wave from a bright supernova that exploded in 1987 has now reached the edge of a cavity around the dead star, reveal new observations with the Hubble Space Telescope and the Chandra X-ray Observatory.As intense heat from the shock wave continues to spread, it will illuminate the dense gas blown off by the detonating star, which was originally about 20 times more massive than our Sun.Called 1987A, the supernova was the brightest recorded in 400 years and exploded in a nearby galaxy called the Large Magellanic Cloud. Astronomers believe that about a million years before the supernova, the star lost most of its outer layers through a slow-moving wind of particles.
The Last Supernova - 1604: 400-Year-Old Explosion Imaged - Space.com - October 2004
Hubble Reveals Dramatic New Phase of a Supernova Explosion Space.com - February 2004
A shock wave from an exploding star known as Supernova 1987A lights up spots in a surrounding ring of dust and gas, in the latest snapshot from the Hubble Space Telescope. It's the most dramatic stellar explosion witnessed in centuries - New images from the Hubble Space Telescope show the dying star's "ring of fire" entering a new phase of brightness
Star Survivor: Companion Endures Explosion Space.com - January 2004
Astronomers have found a bright blue companion star to an exploded supernova,
a stellar survivor to one of the most violent eruptions in the universe.
Where do supernovae come from? Physics Web - August 2003
Hubble looks at dark Universe BBC - April 2003
Astronomers using the Hubble Space Telescope have found two
distant supernovae - exploding stars - that provide new clues
about the accelerating Universe and its mysterious "dark energy".
Hubble looks at dark Universe BBC - April 2003
Thanks to a burster that was remarkably close in cosmic terms,
their true nature may have been revealed. The bursts seem
to come from exploding stars called supernovae.
Astronomers predict stellar explosion for the first time BBC - April 2003
Hubble looks at dark Universe BBC - April 2003
Astronomers using the Hubble Space Telescope have found two
distant supernovae - exploding stars - that provide new clues
about the accelerating Universe and its mysterious "dark energy".
Astronomers Discover "Bulls-Eye" Pulsar In Supernova Remnant June 2002 - Science Daily
This will help scientists better understand how neutron
stars channel enormous amounts of energy into particles
moving near the speed of light.
Supernova lit up the sky 700 years ago - Reuters - April 13, 1999
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