Earth and Space Science Evolution of Stars

The Lives of Stars We can see about 6000 stars with our eyes alone. There are really trillions of them at various stages of evolution. Observing stars at various stages allows us to piece together a model for the life of stars. Our understanding of gravity and nuclear fusion helps as well!!

EM Spectrum The light we see is a very small part of the EM spectrum called the visible light range. The light emitted by stars takes years to arrive to Earth, so we can see stars as they were up to 9 billion years ago!! (Hubble) X-rays are also emitted by objects like black holes and pulsars. Radio waves are emitted from space as radiation left over from the Big Bang. (3K temp of space as a result)

Colour Stars we see appear red-shifted from white light if they are moving away from us (Doppler effect) and blue if they are approaching us. From this, we know the Universe is expanding. Stars also have colour due to their surface temperature. A red star is cooler (3000oC) than a yellow star (6000oC) and a blue star (20000oC to 35ooooC)

Spectra of Light Emitted light from excited gases also emit colours. This spectral analysis of stars allows us to determine what the stars are made up of (which elements). We know our star has an envelope of sodium, for example.

Hertzsprung-Russell Diagram The organization of star evolution is done using the H-R diagram. This graph plots the luminosity (brightness) versus temperature (colour). The Main Sequence stars (about 90% of all stars) run on a diagonal with a negative slope. In the upper right to left hand corners are the super giants and giants. In the lower left corner to the lower right are the white dwarves (red and black too).

White Dwarf

Stellar Evolution Start as nebulae: vast clouds of dust that clump together by gravity. As the mass accumulates, it heats up and if 10 million degrees Celsius is reached: nuclear fusion occurs and a star is born! The evolution of stars depends on its initial mass and the rate at which they burn their fuel. Some live 100 billion years and others only 7 million years! (Our sun is ~5 billion years old).