Life Cycle of a Star

1. Life Cycle of a Star Star Life Cycle: Stars are like humans. They are born, live and then die.

2. Star Life Cycle (5 min)

3. _____________: A dense cloud of gas and dust What is a Nebula? (2 min) Hubble Image Nebulae (6 min) NEBULA

4. _____________ _____________ is the the gas and dust between the stars. This is the material that fills the space between stars. Interstellar Medium

5. The nebula begins to contract due to __________ and the pressure and temperature increase and a _____________ forms. gravity PROTOSTAR

6. When the temperature gets hot enough, _______________ begins and a _______ ____________ star is born. A star that is actively fusing into is a . of stars are main sequence stars. fusion MAIN SEQUENCE hydrogen helium main sequence 90-95%

7. A star loses ____________ during fusion as energy is released. This decreases the star’s gravity. A star will expand, becoming a ___________ ____________, when the outward force of ________________ is greater than the inward force of ______________. mass RED GIANT fusion gravity

8. fusion As the fuel runs out in a star, _________ slows down. When the ______________ force of fusion is less than the ____________ force of gravity, the star will shrink in size, becoming a _________ ____________. outward inward WHITE DWARF White Dwarf A ____________ is a rotating neutron star emitting radio waves. Gamma Rays and Pulsars (8 min) PULSAR

9. SUPERNOVA explosion A ___________________ is an _________________ that marks the end of a very massive star’s life. When it occurs, the exploding star can outshine all of the other stars in the galaxy in total for several days and may leave behind only a crushed core. What is a Supernova? (2 min)

10. The Life Cycle of Stars Depends on Their Mass. Small and medium stars become __________________ once they die. Larger stars become novae and die as: ____________ BLACK DWARVES NEUTRON STAR A neutron star is an imploded core of an exploded star made up almost entirely of neutrons. A teaspoon of their material would weigh more than all of automobiles in the U.S. together The most massive stars become supernovae and die as: ______________________ BLACK HOLE A black hole is an extremely massive remnant from which light cannot escape http://chandra.harvard.edu/photo/2004/rxj1242/index.html

12. Why do larger stars burn their fuel faster and live shorter lives than the Sun? Large, more massive stars have much more _____________ than the sun. This greater internal pressure causes fusion reactions to occur __________. This causes the largest stars to burn their fuel, and eventually run out, much more ______________. Larger stars live shorter _____________. Bigger stars are brighter and hotter due to the rapid rate of __________. gravity quickly quickly lives fusion

13. Where do we get the elements?? All stars spend the majority of their lives fusing __________ into ________________: the main sequence. hydrogen helium When all of the __________ in the central regions is converted to helium, the star will begin to “burn” helium into _______________. hydrogen carbon sun Stars heavier than about 5 times the mass of the ______ can do this with no problem: they burn _____________, and then _______________, and then _____________, _______________, silicon, and so on…until Iron. hydrogen helium carbon oxygen

14. energy Iron is the lightest element that doesn’t release __________ when you attempt to fuse it together. You actually end up with less energy than you started with! So instead of generating pressure to hold up the outer layers, the iron fusion actually takes it out of the core. Thus, there is nothing left to combat ________________ from the outer layers. The result: ___________! gravity collapse This implosion (___________) happens very, very quickly: about 15 seconds. During the collapse, the nuclei in the outer parts of the star are pushed together, so close that elements heavier than __________ are formed. supernova Iron

15. Classifying stars Hertzsprung-Russell or HR diagram Classification system for stars based on Luminosity and Surface Temperature. It’s a graph on which is plotted a star’s brightness (luminosity or absolute magnitude) and color (temperature). In the early 1900’s, the creators of this chart, Ejnar Hertzsprung and Henry Russell charted and classified most of the nearby and brightest stars.