1. Life of Stars

2. Star Birth – Nebular Model Huge clouds of gas and dust occur in space – may be exploded stars Most Nebulae (gas clouds) are invisible – are made visible by light from nearby stars

3. Supernova explosions in cold, dark nebulae trigger the birth of stars.

4. Star Birth Contraction of gas and dust from nova / nebula Gravity increases Temperature increases until the gas begins to glow - called protostars Nuclear fusion – matter begins to fuse into larger elements  star begins to emit visible light.

6. Star Birth Stellar mass and composition determines a stars position as a dwarf, giant or main sequence star 90% of stars are main sequence stars Or if it doesn’t have enough mass - brown dwarfs similar to Jupiter

8. Middle-age to Death The idea of Space – a big recycling center For stars the size of our Sun – Core hydrogen burning will continue for about 10 billion years (age here is a theoretical amount) – Throughout early life a stars gas will exert at least as much pressure out as gravity exerts pressure in

9. As a star uses up more hydrogen its central core compresses – Reason? Harder to fuse heavier elements, meaning less excess energy to heat core, and more mass unable to react. Star swells into a giant or supergiant Nuclear reaction rate increases? Causes a runaway explosion  Helium flash Helium now is fused into Carbon

10. Growth continues until the stars outer envelope is ejected into space as planetary nebula (large amounts of C & He) Star becomes a white dwarf – the intensely bright and “hot” core of the previous star As it cools (loses residual radiant and thermal energy to space) it will become a black dwarf

13. High Mass Stars High mass stars (bigger than 8 to 10 solar masses) don’t experience a helium flash? They continue to fuse He → C → O… and heavier up until iron (Fe) Once the fusion of iron is reached, the core of big stars become unstable Core collapses and explodes in a supernova Such nova may increase a stars brightness by as much as 10,000 times

14. The most famous “before and after” picture Supernova 1987 A

15. Supernova 1987A offers a close-up look at a massive star’s death

17. Other High Mass Star Fates Black Hole (long proposed, Einstein verified?) – Massive stellar objects that not even light can escape the grasp of. – Matter’s interactions around them produce visible light that we can observe – X-ray bursts. – Characteristics are not completely understood, but may have “chemical” analogues. – Presence causes a distortion in light that travels near and around them – gravitational lensing.

18. Other High Mass Star Fates Pulsar – pulsating radio star – Highly magnetized, rotating neutron star – Only visible when emitted radiation is pointing toward Earth – Energy they emit has dramatic effects on material around them – such a nebula and other stars – Proposed in 1934, but first discovered late 1967