Supernovae are vast explosions in which a

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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.
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• 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.

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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 northern sky for 20
years is supernova 1993J in the galaxy M81
which was first seen on March 26 1993.
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• 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.

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• The total amount of energy released in a Type II
  supernova is about 10 53 ergs. About 99 of that
  energy is emitted as neutrinos, whereas only 1
  is converted into the kinetic and heat energy of
  the ejecta (i.e., outer gas layers). Yet enough
  light is emitted by a supernova to make it as
  bright as a billion Suns. The most famous
  historical Type II SN became visible on July 4,
  1054 and was noted by astronomers in Imperial
  China. It was easily visible in broad daylight
  for weeks and did not disappear from nighttime
  skies until 2 years later. At the position where
  the supernova was observed, we now see a glowing
  cloud of gas called the Crab nebula which is
  expanding at thousands of km/s. Near the center
  of the Crab is a strong source of radio waves and
  X-rays called the Crab pulsar. We'll discuss
  pulsars in a minute.

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• The most important supernova that has happened in
  modern astronomical history is known as SN 1987A,
  and became visible, as the name suggests, on
  February 24, 1987. The explosion occurred in a
  nearby satellite galaxy of the Milky Way called
  the Large Magellanic Cloud, so named because it
  was not known to Europeans until Magellan voyaged
  south of the Equator. Because the LMC, as it's
  called, is over 100,000 light years away, the
  explosion actually occurred over 100,000 years
  ago. (Remember that the further out we look in
  space, the further back we are looking in time).
• By studying the spectrum and the apparent
  brightness of SN 1987A, astronomers confirmed
  many of the ideas for how Type II supernovae
  occur. They even had pictures of the star before
  it exploded. It was a blue supergiant star with a
  mass of around 20 and a luminosity of around
  . They found evidence of radioactive Co in the
  SN's spectrum. (This isotope of cobalt is
  radioactive with a short half-life, indicating
  that it was freshly synthesized in the star.)
  Experiments on Earth, which look for neutrinos
  from the Sun, witnessed a sudden burst of
  neutrinos just before the SN became visible,
  supporting another theoretical prediction.

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Supernovae
The explosions of stars with the resulting
release of tremendous amounts of radiation.





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• Two important
  effects of Supernovae
• 1) Many elements are ejected
  into space. 2) Shock wave
  will trigger new star formation.
• Famous Supernovae
• SN 1987A in the Large Magallenic
  Cloud.
• Kepler's Supernova in 1604.
• Tycho's Supernova in 1572.
• Crab Nebula Supernova in 1054.

                                                
                     What's Left Behind? 1)
Neutron Star Pulsar For stars between 8 and 25
solar masses. 2) Black Hole For stars greater
than 25 solar masses.

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M81 SN1993J
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M51 1994/4/8 SN
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Supernovae of Type II are further
subdivided by the way their brightness fades.
In many cases the type II will reach maximum
brightness, dim slightly, and then stay at
almost the same brightness "plateau" for many
days before fading at a fairly regular rate
and are designated Type IIP (II-Plateau).
Other type II supernovae quickly reach
maximum brightness and then dim in a linear
fashion and are classified as Type IIL
(II-Linear).
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• 1885A2003-10-12
• Supernovae Number 2667
• 1885-1988
  661
• 1997
  1270
• 1998ff ( 158
  ) 1428
• 1999gw ( 204 )
  1632
• 2000ft ( 176
  ) 1808
• 2001ke ( 291 )
  2099
• 2002ld ( 316
  ) 2415
• 2003ir ( 252
  ) 2667

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• The article from Cappellaro et al. presents a
  synthetic view of the problem. We only give a
  summary of this paper. The rate of supernovae
  depends on the supernovae type and the host
  galaxy type according to the Hubble sequence. The
  average value for the supernovae rate is 0.68 SNu
  (1 SNu 1 SN per century per 1010 L ). Table
  gives a detailed description of the rates. It
  should be noticed that SN Ib/c and SN II (which
  are due to young stars) never occur in elliptical
  galaxies which contain only old stars.

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Type II are due to the formation of neutron stars
and the subsequent 'core bounce' of infalling
matter. In Type I the energy generated is due to
thermonuclear processes whereas in TypeII the
energy source is indefinite. Astrophysicists are
still unsure of the exact processes that give
rise to supernovae and what has been described
are based on computer models of stellar
structure. Supernovae are not frequently seen .An
unprecedented opportunity to observe one at close
range presented itself in 1987.
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Supernovae of Type II occur at the end of the
evolution of massive stars. The phenomenon
begins when the iron core of the star exceeds a
Chandrasekhar mass. The collapse of that core
under gravity is well understood and takes a
fraction of a second. To understand the
phenomenon, a detailed knowledge of the equation
of state at the relevant densities and
temperatures is required. After collapse, the
shock wave moves outward, but probably does not
succeed in expelling the mass of the star. The
most likely mechanism to do so is the absorption
of neutrinos from the core by the material at
medium distances. Observations and theory
connected with SN 1987A are discussed, as are the
conditions just before collapse and the emission
of neutrinos by the collapsed core. -Bethe H A
Rev.Modern Phys 62, 801
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  ?,

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  ?????????.??????????,???????????????????????????,?
  ????????1051erg,?????????????????????,???SN??????(
  prompt explosion).???????????????????????,???????
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  elayed explosion).?
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Because little entropy is produced, nucleons
remain in nuclei down to nuclear touching
densities. Thus, the collapse cannot be stopped
above nuclear matter densities. This is
illustrated in the following comparison of the
adiabatic index against the Newtonian value of
4/3 for gravitational stability,
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A 2D simulation of a Type II SNe explosion The
matter is heated By neutrinos from The hot
proto-neutron Star .Entropies are Given in units
of kB/ Nucleon.
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The explosive processing and nucleosynthesis in
the ejecta gives rise to a large fraction of the
present day element abundances. Explosive
nucleosynthesis calculations require the
knowledge of nuclear reaction rates at high
temperatures, to a large extent for unstable
nuclei, based on theoretical or experimental
efforts. The comparison with abundances from
specific supernova observations can probe the
correctness of the stellar evolution treatment
and the 12C( a,? )16O rate. SN 1987A showed
reasonable agreement with C, O, Si, Cl, and Ar
abundance observations.
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An x-ray image of the Crab Pulsar at center of
the Crab Nebula. Photograph from CHANDRA website
click picture to go to website. 
An x-ray image of the Crab Pulsar at center of
the Crab Nebula. Photograph from CHANDRA website
click picture to go to website. 
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