GCSE Physics: Stars and GalaxiesStars
Stars are formed by hydrogen gas condensing. Hydrogen changed to helium by nuclear fusion. As the gas atoms move closer together their speed increases. These atoms collide which transfers kinetic energy to heat energy. The temperature of the start will reach about fifteen million K. The hotter the star is the brighter it will be.
The main types of stars are: red dwarfs, yellow stars, blue giants, giant stars and super stars. Near the end of a stars life the star will get a lot bigger becoming a giant/super giant star. The star will eventually explode forming a planetary nebular or a supernova depending on mass.
The sun is a yellow star. It will live for ten billion years. At the end of its life it will swell up becoming very large. It will grow large enough to engulf the planets in the solar system including the earth. Eventually it will shrink again leaving behind a lot of gas. This gas will form a planetary nebular.
A galaxy is billions of stars, dust and gas held together by gravity. Galaxies are scattered throughout the universe. Groups of galaxies are formed when gravity gradually pulled large amounts of gas together. Galaxies vary in shape and size. Not all galaxies look alike.
In 1926, an astronomer named Edward Hubble decided to classify the galaxies, grouping them according to some logical scheme.
After considering different schemes, he decided to arrange or group them by shapes. He would classify them according to the way they looked. In Science, the study of something according to its form or structure is called mornophology.
Some of the typical galaxy shapes are:
- Elliptical Galaxy
- Spiral Galaxy
- Barred Spiral Galaxy
Our galaxy is the Milky way. The milky way is a spiral galaxy. The nearest group of galaxies to ours is the Virgo Cluster, and the nearest galaxy is called Sagdeg.
- The sun will end when it runs out of its current fuel hydrogen. It will start to cool down, expand and turn into a red giant which could go out as far as Jupiter
- The sun is a typical G2 star
- The first step in star formation is when part of the interstellar medium (the matter between stars and composed of gas and dust - intermixed throughout all of space) collapses because of its own weight. The star heats up and get smaller and smaller. The core bcomes how enough for a nuclear reaction to begin
- Star types are catalogues according to spectral type by the letters O, B, A, F, G, K and M. "Oh be a fine girl/guy and kiss me"
- O-type stars are the hottest stars and M-type stars are the coolest.
- Our galaxy is the spiral shape with several arms
- The closest known neighbouring galaxy is the Magellanic Clouds. The milky way is 10 times as big as the Magellanic clouds.
- A galaxy is a gravitationally bound collection of stars and gas
- There are three types of galaxies
- Elliptical Galaxies
- Names by E0 to E7
- E for elliptical
- 0 means a ball shaped galaxy
- 7 means throwing discus shape
- Lenticular galaxy
- Shaped like a lens in a magnifying glass
- Barred spiral galaxies
- Names SBX
- Where X is the lower case letter as in the unbarred cases above. This is the type of galaxy we are in.
- Elliptical Galaxies