STELLAR EVOLUTION

1. STELLAR EVOLUTION The life cycle of stars.

2. EMPTY SPACE? • So called empty space actually has a density of .1 to 1 particles per cubic centimeter. • Also present are quantum virtual particle pairs and all sorts of energetic disturbances such as supernova shock waves, gravity waves, and radiation.

3. GIANT MOLECULAR CLOUD • Gravity sometimes accretes material to increase the density of space. • Giant molecular clouds have densities ranging from 10 to one million particles per cubic centimeter.

4. GRAVITATIONAL COLLAPSE • Mechanism of gravitational collapse is unknown but might be caused by shock waves. • The GMC collapses and fragments to form Bok Globules (star forming cocoons).

5. PROTOSTAR FORMATION • The loss of gravitational potential energy causes heating. • Protostars fall into three categories depending on their mass. • Small protostars less than .1 solar mass (SM). • Medium protostars 1-50 SM. • Massive protostars >50 SM.

6. PROTOSTAR

7. FAILED STARS • Less than .1 SM does not have enough mass to produce fusion. • These Brown Dwarfs are very numerous and may account for some of the “dark matter” theorized by cosmologists.

8. FUSION BEGINS • Protostars with masses of >.6 SM undergo gravitational collapse. • Heat and pressure increase until hydrogen fusion begins. • The “birth of the star” blows away dust and gas from the cocoon. • These new stars become Main sequence stars.

9. A STAR NURSERY

10. MAIN SEQUENCE STARS • Burn hydrogen in their cores. • They establish hydrostatic equilibrium. • Outward pressure from fusion and the Coulomb force = inward force due to gravity.

11. SMALL MAIN SEQUENCE STAR • Mass is .5 SM or less. • Live for hundreds of billions of years. • Usually called COOL RED DWARF STARS.

12. MID SIZED STARS • Mass is .6 – 5.4 SM. • Live for approximately 10 billion years. • Our sun is a mid sized main sequence star.

13. GIANT STARS • Live for only a few million years. • They are between 10-20 SM. • They burn their hydrogen very rapidly to maintain hydrostatic equilibrium.

14. GOING OFF MAIN SEQUENCE • After all of the hydrogen fuses, the star undergoes main sequence turnoff. • The hydrostatic pressure decreases and the star begins collapse. • Wolf Rayet type stars.

15. GERIATRIC LOW MASS STARS • Stars less than .5 SM. • Too small to fuse helium. • Fade and evaporate to form Brown Dwarf Stars.

16. MEDIUM STAR • Stars less than 3.4 SM. • Helium fuses to form carbon. • Luminosity and core temperature increase. • Surrounding gas bloats out to form a Red Giant.

17. RED GIANT DEMISE • Large energy pulsations eject most of the solar material. • This material may recycle to form new stars. • The star shrinks to form a White Dwarf.

18. BINARY SYSTEM WHITE DWARF • A white dwarf in a binary system can accrete material from its partner star to build up mass again. • Little hydrostatic pressure causes rapid collapse and a Type 1A supernova.

19. GIANT OR SUPER GIANT STAR • Stars of > 3.5 SM. • Huge gravitational pressure collapses the core. • Temperatures increases and fusion continues until Iron is formed. • Iron can not undergo fusion and the hydrostatic pressure drops.

20. CORE COLLAPSE • Rapid end of fusion causes very fast core collapse. • The collapse happens in a fraction of a second. • This causes a Type 2 supernova.

21. NEUTRINO SHOCK WAVES • The supernova causes shock waves of neutrinos. • Most of the stellar material is blasted out into space. • The escaping material is bombarded with neutrinos. • The neutrinos are captured and elements heavier than iron are formed.

22. SMALL STARS • Stars < 1.5 SM. • Gravity collapses them until electron degeneracy stops collapse. • White dwarf forms. • Evaporates to form a Black Dwarf.

23. MID SIZED STARS • Mass is > 1.4 and < 3 SM. • The collapse forces the electrons into the nucleus where they combine with protons to form neutrons. • Neutron or quark stars are formed.

24. MASSIVE STARS • Mass > 3 SM. • Gravity overcomes neutron degeneracy and collapses the core to form a Singularity. • A black hole results.