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Author: Janet Sumner
  • Video
  • 10 minutes

Making stars

Updated Friday, 6th July 2007
Dr Janet Sumner visits a project looking for a source of cheap, clean fuel, which gives us a glimpse of the birth of our sun

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There aren’t many people who can say they’ve got a star named after them, but I can.

This is my star…

A close-up of Janet's star

A 10 metre cubed doughnut of plasma with a staggering temperature of tens of million degrees centigrade! It might not be as big as, but it is hotter than, the sun – our nearest star.

So how did Janet’s Star come into being? Well, I am one of the presenters on the Open University/BBC series The Cosmos: A Beginner's Guide, and since the cosmos is full of stars, I was sent to an ordinary looking warehouse in the heart of Oxfordshire, where stars are made, one every 15 minutes.

Normal stars, like our sun, form when huge clouds of hydrogen atoms succumb to gravity and collapse in on themselves - the electrons are stripped away from the atoms to form plasma. The intense heat and pressure in the core of the newly formed star cause the hydrogen atoms in the plasma to smash together and create heavier elements like helium and it's this energetic process that releases enough energy to make the star shine. It's called nuclear fusion and a group of experts - the MAST team at the UK Atomic Energy Authority facility in Culham near Oxford - are making it happen here on earth.

The question is, why?

Nuclear fusion creates a huge amount of energy: enough to make the stars twinkle in the night sky. Our sun produces 386 billion billion mega joules every second; that’s enough to heat 744 billion cups of tea for every single person on earth. All you need is the right gas and enough heat to kickstart the fusion process which then becomes self-sustaining. The end product is energy - lots of it, and what’s more, it’s safe, clean and environmentally friendly energy. Sounds like the solution to all our problems? Well, the team at Culham certainly think so, which is why they are reproducing the sun’s nuclear fusion on a smaller scale in the hope of one day harnessing all that energy to make electricity.

So how do they do it? It all happens in a special device called a tokamak (A Russian acronym roughly translated as "magnetic bottle")

Janet in front of the Tokamok

Janet in front of the Tokamak

The tokamak is a sealed vacuum vessel. A small amount of gas is pumped into it, and then heated up to a hundred million degrees centigrade (yes, pause for thought – that is a hundred million degrees centigrade!). The gas used is hydrogen, but a type different from the 'normal' hydrogen used for nuclear fusion on our sun. This is too slow and inefficient for us to use here on earth, so the MAST team use a different form of hydrogen – deuterium, the kind of hydrogen that’s found in “heavy water”. Normal hydrogen fuses slowly – which is why our sun will last for 10 billion years. If it used deuterium it would have burned out in just 1 second.

A huge array of magnets is used to constrain the gas in the chamber, - taking the role played by gravity in real stars. The pressure on the hydrogen (deuterium) gas is increased until it starts to fuse. This is exactly what happens in a real star; in fact, the stars created at MAST are so much like our sun they even make their own solar flares

Star plasma

Janet's star flares: the plasma during an ELM solar eruption

Close-up colour-altered image showing solar flare

A zoomed-in view with modified colour to show similarity with solar flares

The reaction happens so incredibly fast, that the team capture the stars formation on high speed camera and play it back in slow motion:

(Video clip made by the Cosmos production team)


Our slow motion video clip shows you the birth, life and death of Janet’s Star. The super-heated hydrogen gas creates a plasma - this appears as an expanding pink doughnut spinning out from a central pole, rather like spinning candy floss. The pink colour is cooler plasma, the central portion is transparent because it’s too hot to emit visible light.

The plasma ball tries to expand but is prevented from doing so by the strong magnetic field. Eventually the star begins to 'wobble' and become unstable because it is being forced into a shape it doesn't want to be.

Finally it disappears in a bright flash of pink and vanishes.

In the cosmos, older stars 'die' when they have run out of their hydrogen fuel and begin to use other chemicals contained in them to try to continue the reaction.

They start by fusing the helium they made out of the hydrogen and continue the process, becoming massive, slowly cooling, cosmic ovens known as red giants cooking up oxygen, carbon and iron and all the other elements we find on earth.

When the star has fused all the atoms it can, it stops reacting. If the star is big enough this produces a massive explosion - what’s called a supernova. This scatters all the elements that were created in the star across the universe and even creates new elements in the process – this becomes in fact, the very stardust from which we ourselves are made.

Now, have a look at my star again and see if you can spot the different stages, the birth; as fusion starts, the expanding plasma, the 'wobble' and finally; the bright pink flare as the plasma cools and stops, Janet's Star dies.

Those of you with sharp eyes will notice some brightly coloured particles flaring to the right of the plasma ball. Well, mine was in fact a dirty star – those brightly coloured particles represent a stream of impurities that the team were injecting into the chamber to see how the 'star' or fusion process would react to a less than pure input of gas.

If you’ve enjoyed learning about ‘Janet’s Star’ and wish to discuss anything related to stars or nuclear fusion, you can enter into a discussion on our comments area.


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