An erupting, massive star in the Milky Way. NASA's Hubble Space Telescope has identified one of the most massive stars known, emitting as much as 10 million times the power of our Sun and with a radius larger than the distance between the Sun and the Earth.
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Image courtesy of NASA, Space Telescope Institute
Fusion Inside the Stars
Fusion in the core of the stars is achieved when the density and
temperature arising
from the gravitational pressure are high enough.
There are different fusion cycles that occur in different phases of the
life of a star .
The first stage is the fusion of Hydrogen
into Helium. This is the stage that our Sun is in.
In stars with a very high temperature (greater than 16 million degrees
Kelvin)
another set of fusion reactions, the so called Carbon-Nitrogen-Oxygen
(CNO) cycle can take place.
Here the Carbon atom is a catalyst for the
reaction: it participates but it is not "burned".
At still higher temperatures,
Helium burning
produces Carbon. Finally, at even higher temperatures
the heavier elements up to Iron are formed by fusion of
Carbon, Oxygen and Silicon.
To create elements heavier than Iron,
neutron capture
must occur. This can happen in a
Supernova, when
a very massive star explodes at the end of its life
cycle.
As a result of the fusion reactions occurring in the Sun and stars,
neutrinos are emitted through the process of
beta decayand reach Earth. By
detecting these neutrinos, scientists learn about
fusion inside the stars.
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