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Supernovas are the most powerful and spectacular
outbursts known in nature. What is called a Type II supernova is due to the
collapse of a massive star, at least eight times as massive as the sun, that
has used up its main nuclear fuel and produced a nickel-iron core. When this
core can no longer support the pressure of the star’s outer layers, it
collapses to form a neutron star of immense density. Over 2,500 million tons
of neutron star material could be packed into a matchbox. Its temperature is
around 100.000 million degrees centigrade. Multitudes of neutrons are
produced in the collapsed star, which pass directly through the start into
space, and this release of neutrons causes the core to respond with a shock
wave that moves outward. When it meets the material that is falling inward,
the result is a catastrophic only a small, incredibly dense remnant that may
be a neutron star or, in extreme cases, a black hole.
A supernova is often more than 500 million times as luminous as
the sun. A supernova remnant (SNR) may be detectable as a pulsar, an example
of which is the Crab Nebula, known to be a remnant of the supernova observed
in the year 1054. The 1987 supernova in the Large Cloud of Magellan had a
low peak luminosity by supernova standards, only about 250 million times
that of the sun. At its brightest the supernova shone as a star between
magnitudes 2 and 3, even though it was 170,000 light-years away.
1) What is the main topic of the passage?
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