2.3.5 Supergiant stars

What happens to supergiant stars?

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NARRATOR 1:

Some stars, however, are much more massive than the sun and they lead very different lives. They’re able to fuse heavier and heavier elements inside their core. The star gets bigger and bigger. Some grow up to 1,000 times the size of our sun until it has fused elements all the way up to iron.

NARRATOR 2:

And once we’ve formed an iron core, there's no more energy can be got from fusion, that core collapses. The rest of the star starts to collapse in after it, but then it bounces off. There’s a huge shock wave. And in just a second, bang, the outer parts of the star are blasted off into space in a huge supernova explosion. These supernova explosions are so powerful that when one of the stars explodes it can actually outshine the whole galaxy of which it’s part, a galaxy of maybe a hundred thousand million stars.

NARRATOR 1:

For these super giant stars, all that is left is the super dense core known as a neutron star-- an object that can have a mass greater than our sun, but be less than 20 kilometres across. But for the most massive stars of all, we think when the core collapses the gravity is so strong it becomes a black hole from which not even light can escape.

NARRATOR 2:

So stars are actually the places in the universe where the elements are created.

NARRATOR 1:

After the big bang, our universe contained only hydrogen and helium. All the other heavier elements were therefore fused inside stars.

NARRATOR 2:

The amazing thing is that virtually everything you see around you was made inside a star billions of years ago before the sun and the planets were formed. And when that star died and blasted its guts out into space, that formed the raw materials from which our sun, the planet Earth, and indeed ourselves were made. And actually, I think ultimately that's one of the major reasons why I think understanding stars is crucial, because it’s actually telling us where we came from.

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As with low mass, Sun-type stars, the extra sources of energy cause the star to expand and then cool, although their higher temperatures mean that they usually turn into hot blue or blue-white supergiants.

A great example of a supergiant is Rigel from the Orion constellation.

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Figure 14 Evolutionary track of a high-mass star across the HR diagram 

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This graph shows the evolutionary track of a high-mass star.

Figure 14 Evolutionary track of a high-mass star across the HR diagram 

On the graph in Figure 14, the evolutionary path of a massive star is shown. The hot, blue supergiant evolves to even greater sizes and cooler temperatures, passing through both yellow and blue supergiant phases.

The largest of all known stars are the red supergiants, like Betelgeuse in the Orion constellation. If a red supergiant were placed in the centre of our Solar System, its radius would reach out past Jupiter!

The video explains what happens when the temperature rises further. You can read more about this process in the next section.