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Stargazing; Shedding light on supernovas and the Big Bang.

YOU might remember the phrase from Joni Mitchell's song Woodstock: "We are stardust." Well, it is actually true.

When the Big Bang started everything off, the universe was a seething mass of protons and neutrons.

These began to fuse to create the lightest elements, primarily hydrogen and helium with a little amount of lithium.

As the clouds of matter began to condense under the force of gravity, they began to heat up, becoming the dense balls of hot gas we call stars.

The energy source in stars is the energy that is released as hydrogen fuses together to make the heavier helium.

Stars live for many millions of years this way, but it is as the hydrogen runs out that things get interesting.

It all depends on how massive the star is. The lightest ones don't have enough gravity to heat the core hot enough to fuse anything other than hydrogen, so when they run out of hydrogen nothing else happens.

For more averagely massive ones, such as our Sun, gravity is strong enough to make helium fuse to make oxygen and carbon, but that's where they run out too.

The most massive ones can even fuse the heavier elements up to iron but even they run out there.

So how are the elements heavier than iron created? As the heaviest of stars run out of fuel, the light pressure preventing gravity collapsing the star reduces and the star collapses in on itself.

As they collapse, the momentum and energy is great enough to fuse the heavier elements in an instant but this has a catastrophic effect on the star - causing it to explode violently, cascading all the newly fused material out into space. This is a supernova explosion.

This material flows out into space at extremely high speed and intermingles with other clouds, eventually slowing down enough for gravity to take over and allow the clouds to collapse again, eventually forming second generation stars with heavier elements in them.

Our sun is actually a third generation star so this life and death process happened twice before to make our star have the atomic structure it does. We know this from spectroscopic analysis of the light that it shines, which tells us all about what material is present in its core.

Supernovae aren't that common locally. The last one in our near neighbourhood was about a thousand years ago. In 1054AD Chinese astronomers recorded a new star visible in daylight that we now know was a supernova, which left a gas cloud we call the Crab Nebula.

One of the best candidates for the next supernova is Betelgeuse, which could go any time soon.

As it is 60 light years away, it may even have gone already and the light is on its way - now wouldn't that be cool? ? Robert Ince is the resident astronomer and manager at the Scottish Dark Sky Observatory, near Dalmellington, Ayrshire.

It is a public facility dedicated to opening up the science, art and nature of the dark skies for all. For info, visit


EXPLOSIVE n An idea of how the Big Bang looked
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Title Annotation:Letters
Publication:Daily Record (Glasgow, Scotland)
Date:Aug 17, 2013
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