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What is the difference between a red giant and a neutron star?
During
the life cycle of a star, as the star consumes a significant percentage of the
hydrogen fuel in its core, the nuclear reaction decreases and the out force of
the radiant energy weakens. The core of the star further contracts because its
gravitational pull becomes more than the out-force of radiant energy. But this
raises the temperature of the core. Meanwhile, the hydrogen nuclei 'burn' in
the outer layer or shell surrounding the core.
The extra heat from the core as well as the
heat generated in the outer layers causes the star's outer region to 'boil' and
expand. The star becomes big and its brightness increases. But, as the outer
layer expands farther away from the nuclear furnace, its temperature falls. The
puffed-up star looks red and cool. If it is many times more massive than the
Sun, it becomes a red supergiant. If it is sun-sized or only slightly more
massive than the Sun, it becomes a slightly swollen red giant.
The red
giant stage of a star is a relatively short stage. In this stage, the star
consumes its hydrogen at a very fast rate, piling up helium in its core. As the
fuel burns, the core contracts further, producing temperatures as high as 100
million
At this point, the helium nuclei in the core
fuse together in another nuclear reaction to form carbon nuclei. This is a
critically unstable moment in a star's life with two layers of the star burning
at the same time-an outer layer where hydrogen is being turned into helium and
inner core where helium is being turned into carbon. Hereafter the fate of the
star depends on the mass of its core. If the core mass of the star is in the
range 1.4M--3Mo or the star mass is between 8M to 15 M,, the
core shrinks to a radius of about 10 km and a neutron star is formed. If a
neutron star is born rotating very fast, it emits electromagnetic radiation,
which astronomers detect as pulses of radio waves. Such stars are called pulsars.
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