Wouldn't it be fascinating to know what it's actually like inside a star? After reading this you'll have an idea about the life of a star and how it shines. Why stars appear different colours is addressed, along with measuring stars' vibrations and techniques to "look into" our Sun and other stars. Astronomers don't have all the answers though, and this feature finishes with some questions that hopefully one day we will be able to crack!
The Ins and Outs of a Star
Our Sun is a more interesting place than many realise!
Image credit: SOHO (ESA & NASA).
Wouldn't it be cool to know what it is like inside a star? Actually it is very hot in there, a few million degrees, and matter is in an interesting state. At these temperatures it is not solid, not liquid and not a gas, but a plasma: the fourth state of matter! In this article I will explain what we know about the inner structures and lives of stars, and how we can look "inside" them.
The evolution of a star has something in common with humans. A star is born, matures, ages and dies. It is not born from seeds or eggs, as we see for animals or people, but from a dust cloud. This cloud becomes denser and hotter over time, as gravity pulls all the dust particles together. At a certain point when this cloud is both dense and hot enough it becomes plasma and starts fusing hydrogen to helium. This produces a lot of energy and the star starts to shine.
Around the core, which is the engine of the star and where the fusion takes place, is a large atmosphere of gas. It consists of different layers, like our own planet's atmosphere, and in the different layers there can be greatly varying conditions. It can be very turbulent; a convective zone, or very calm; a radiative zone. This has an influence on the energy flowing from the core to the surface where we see it shining. These layers change over time, as the star gets older.
We think of our Sun as being gigantic and it is, but compared so some other types of star, it's quite tiny!
Image credit: NASA, ESA and A. Feild (STScI).
Red hot!
The colour of a star depends on the temperature of its surface. When very hot it is white, and when slightly cooler it appears blue, yellow, orange and red. You can see a similar example of this yourself when you burn a candle. Close to the wick where it is hottest it is white and further outward the colours change from blue to yellow, orange and red.
Our Sun is a mature yellow star and it will remain like this for another four billion years. Sometime after, it will run out of hydrogen, its fuel. This will not be the end of our star, but it will require a new fuel source. This will be helium, the ashes of the first burning process. However, before it can use helium the core of the star must grow hotter still. So the core becomes even more heated and dense for the star's "second burning life", but the star is now old and this cannot continue. Our Sun will just die quietly when it has burned all its helium, but heavier stars die in explosions like fireworks!
Good vibrations
Now we know a little bit about a star's life, it is time to explain how we can look into a star. Actually it is done the same way that we look inside the Earth. For instance when there is an earthquake, the Earth shakes, but not all material inside the Earth responds in the same way, and due to this difference we can derive what type of material is present in a certain place. For example, you can hear the difference in material when you induce vibrations upon it by knocking on a wooden, metal or glass door. We use this same technique on stars.
