Twinkle, twinkle

What emotions are conjured up when you look up at the sky on
a cloudless night? Are you awe-struck by the vastness of the
heavens? Have you wondered what is happening up there, among
those sparkling pinpricks of light we call stars, so impressive in
number yet each appearing so insignificant? It is easy to forget
what they really are: gigantic cauldrons of fire, millions of times
bigger than the Earth. For stars are so distant that it would take
our fastest rockets many years to reach even our closest neighbour.
But there is a star that our rockets could reach in a matter of
months.
The closest star to Earth is an old friend. Without it we would
not be here. Our Sun sustains nearly all life on Earth with its
warmth and light. The heat generated inside it and radiated out
to bathe its planets is somethingweall take for granted. The author
Douglas Adams sums up our indifference wonderfully:
‘‘Several billion trillion tons of superhot exploding hydrogen nuclei
rose slowly above the horizon and managed to look small, cold and
slightly damp.”
Stars come in many different colours and sizes and our Sun is
pretty average. It is middle-aged and rather on the small side. An
astrophysicist will tell you that it is a yellow, main sequence, G2
dwarf star. Doesn’t sound very impressive does it? Almost a bit
embarrassing. You can just imagine the intergalactic snobbery as
visiting aliens from big, white classAstars like Vega or Sirius look
down their ears at us (their noses being on top of their heads). But
in the domain of stars, being small has its advantages.
All stars have a certain life expectancy which can vary from a
million to many billions of years. It all depends on what is going
on inside them and this depends ultimately on their mass, which
is a measure of how much matter they contain. So what goes on
inside a star? We now know that all stars are like cosmic cooking
pots. Most of the atoms that make up your body were synthesized
inside some star long before the Sun and our solar system were
even made; a star, moreover, that no longer exists. I amaware that
it appears we are being side-tracked from our main story of how a black hole is created, but the life cycle of a star is crucial to this story. Stars go through several quite different phases during their
lifetime, each more fascinating than the last.