超星与中子星
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超新星和中子星
北京师范大学天文系 李宗伟
Supernovae are vast explosions in which a whole star is blown up. They are mostly seen in distant galaxies as `new' stars appearing close to the galaxy of which they are members. They are extremely bright, rivalling, for a few days, the combined light output of all the rest of the stars in the galaxy. As most observed supernovae occur in very distant galaxies they are too faint even for the largest telescopes to be able to study them in great detail. Occasionally they occur in nearby galaxies and then a detailed study in many different wavebands is possible.
• Supernovae Type II • This sudden collapse of a massive star's core into a volume over a million times smaller than its original volume is really bad news for the star. The outer layers of the star come raining down onto the core. Somehow this collapse changes into an explosion: a type II supernova. The process by which this happens is still being investigated, but evidently the core collapses to something below its equilibrium radius and then rebounds slightly. That bounce transfers an enormous amount of energy to the layers falling down from above. Just watch that smaller ball take off after they hit the ground!) A strong wave of energy--a shock wave--travels out through the envelope and heats the star so much that the outer layers are blown away. Another important effect is the huge numbers of neutrinos that are produced when the neutron star is formed. Ordinarily, neutrinos don't interact much with matter, but these neutrinos are so numerous and energetic that they help push the outer layers of the star away.
• The formation of the neutron star happens extremely rapidly and once neutron-degeneracy pressure is established the core becomes rigid. The collapse of the star is dramatically halted and the infalling material bounces off the core and starts moving up towards the stars surface. A shock wave of tremendous energy is generated moving at supersonic speeds (5-10 000km s-1) blowing off the rest of the star's outer layers. The neutrinos produced by inverse beta decay swiftly travel out of the core, carrying up to 100 times more energy than is emitted as electromagnetic radiation. This gigantic explosion is called a supernova and can produce enough energy to temporarily outshine the whole galaxy! An energy of 1044 J is normally observed in supernova events.
The last supernova to be seen in our galaxy, the Milky Way system, was seen in 1604 by the famous astronomer Kepler. The brightest since then was supernova 1987A in the Large Magellanic Cloud, a small satellite galaxy to the Milky Way. The brightest supernova in the north源自文库rn sky for 20 years is supernova 1993J in the galaxy M81 which was first seen on March 26 1993.
北京师范大学天文系 李宗伟
Supernovae are vast explosions in which a whole star is blown up. They are mostly seen in distant galaxies as `new' stars appearing close to the galaxy of which they are members. They are extremely bright, rivalling, for a few days, the combined light output of all the rest of the stars in the galaxy. As most observed supernovae occur in very distant galaxies they are too faint even for the largest telescopes to be able to study them in great detail. Occasionally they occur in nearby galaxies and then a detailed study in many different wavebands is possible.
• Supernovae Type II • This sudden collapse of a massive star's core into a volume over a million times smaller than its original volume is really bad news for the star. The outer layers of the star come raining down onto the core. Somehow this collapse changes into an explosion: a type II supernova. The process by which this happens is still being investigated, but evidently the core collapses to something below its equilibrium radius and then rebounds slightly. That bounce transfers an enormous amount of energy to the layers falling down from above. Just watch that smaller ball take off after they hit the ground!) A strong wave of energy--a shock wave--travels out through the envelope and heats the star so much that the outer layers are blown away. Another important effect is the huge numbers of neutrinos that are produced when the neutron star is formed. Ordinarily, neutrinos don't interact much with matter, but these neutrinos are so numerous and energetic that they help push the outer layers of the star away.
• The formation of the neutron star happens extremely rapidly and once neutron-degeneracy pressure is established the core becomes rigid. The collapse of the star is dramatically halted and the infalling material bounces off the core and starts moving up towards the stars surface. A shock wave of tremendous energy is generated moving at supersonic speeds (5-10 000km s-1) blowing off the rest of the star's outer layers. The neutrinos produced by inverse beta decay swiftly travel out of the core, carrying up to 100 times more energy than is emitted as electromagnetic radiation. This gigantic explosion is called a supernova and can produce enough energy to temporarily outshine the whole galaxy! An energy of 1044 J is normally observed in supernova events.
The last supernova to be seen in our galaxy, the Milky Way system, was seen in 1604 by the famous astronomer Kepler. The brightest since then was supernova 1987A in the Large Magellanic Cloud, a small satellite galaxy to the Milky Way. The brightest supernova in the north源自文库rn sky for 20 years is supernova 1993J in the galaxy M81 which was first seen on March 26 1993.