Properties of Stars

Solar Nebula Theory Page 383 Plus handout https://www.youtube.com/watch?v=9EnBBIx6XkM

Brightness A star can be bright because of it’s size and proximity to earth Stars also differ in their Luminosity (how much energy a star radiates per second)

Temperature Determined by colour Stars vary in colour Red (coolest @ 1000 oC) Yellow (like our sun @ 6000 oC) Blue (Hottest @ 30000 oC) Colour can tell us about a star’s composition by analyzing spectral patterns

Size and Mass Can be calculated by using luminosity and temperature Stars vary greatly in size Dwarf stars (0.1 the sun’s radius) Massive stars (1000 x the sun’s radius)

Hertzsprung-Russell Diagram (P.376)

A Star’s Life Cycle Gravity compresses a nebula and the temperature rises to 10 000 000 oC Fusion begins in the core (conversion of H into He) The star “turns on” The star’s gravity helps to keep the star from expanding due to high temperatures. It is therefore a “stable star” Nebula

Question… What happens when the fuel runs out?

Answer… It depends on the mass of the star!

~The Evolution of Stars~ Low Mass Stars Red dwarfs Burn H slowly (100 billion years) Eventually lose mass and turn into a white dwarf (small, hot and dim)

Intermediate Mass Stars –Our Sun’s Fate Consumes H faster (10 billion years) Once all H is used up, Helium will become the new fuel and extreme heat in core will cause expansion Outside layers will become much cooler and it will turn into a red giant

A Red Giant At this point our sun (now a red giant) will engulf the four inner planets of our solar system Then it will most likely lose mass and turn into a white dwarf then into a very small, dense, hot and dim black dwarf star

Our Sun’s Fate White dwarf Black dwarf

Massive Stars Massive stars consume Hydrogen rapidly and swell into Supergiants Fusion stops, the star collapses and a supernova occurs

Supernova – Going out with a bang! The spectacular death of a massive star The light from the “explosion” can take a long time to reach earth which makes them difficult to spot (a needle in a haystack)

Spotting a supernova – A needle in a haystack

An illustration of a Black hole Black Holes After a supernova a neutron star or a black hole forms (depending on mass). Black holes are so dense that not even light can escape them! An illustration of a Black hole