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brightest thing in the X-ray sky is the Sun, because it
is so close. The X-rays are produced by gas that is more
than a million degrees Celsius in the corona of the star
(the bit you can see during total eclipse- as seen in
Picture 6). The gas is heated by the ever-changing magnetic
fields of the star. Sometimes a whole lot of energy can
be released in one go as stellar flares; the star can
become hundreds of times brighter in X-rays during a flare!
We can only see X-rays from ordinary stars if they are
relatively close (a few hundred light years- still a long
way.) For example the X-ray power of the Sun is the same
as about 50 power stations per person on Earth - and stellar
flares can be 10,000 times more than this!
The picture on the next page shows an X-ray view of
the Sun: you can see a huge amount of detail as the
X-ray hot gases in the Sun’s corona follow the
fantastically complicated magnetic fields. However,
the Sun is about a million times fainter in X-rays than
in visible light; so for us to see other star systems
in X-rays they have to be doing something amazing. When
X-ray astronomy took off in the 1960s (literally), we
found the universe to be more dynamic and extreme than
we’d ever imagined!
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