In the night sky: Orion
In the night sky: Orion

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In the night sky: Orion

2.1.6 Birth of a star

How is a star formed?

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But way out there in space, there’s huge clouds of dust and gas. And if one of those clouds of dust and gas is massive enough, its own gravity causes it to start to collapse. So it folds in on itself, and towards the centre of that cloud it gets denser and denser. It gets hotter and hotter.
And eventually, the particles that the gas and the dust are made of are brought so close together that they start to stick together. They start to fuse. That’s the energy source of a star. The star switches on and begins to shine.
Inside every newborn star, hydrogen atoms are fused together to make helium. This process is called fusion, and it creates the energy that powers every star.
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Stars form in clouds of dust and gas called giant molecular clouds, the debris of old stars. The constellation of Orion includes the molecular cloud complex we know as the Orion Nebula.

While the density of dust and gas in a giant molecular cloud is high compared with the rest of interstellar space, in comparison with the atmosphere of the Earth, they are a thousand million million times less dense.

The dust and gas cloud is highly structured, with lots of clumps where the dust and gas is slightly more dense. These relatively high density areas are where star formation will occur.

Initially, the clumps are quite stable, but once a clump is sufficiently dense, it will start to contract under its own gravity. As it contracts, the temperature rises. Eventually, after further collapse and fragmentation, a protostar develops. After only a few thousand years, the surface temperature of the protostar will have risen to 2000–3000 K!

In the next section, you will take a closer look at the Orion Nebula.


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