Pearson Prentice Hall Physical Science: Concepts in Action Chapter 26 Exploring the Universe

1. Pearson Prentice Hall Physical Science: Concepts in Action Chapter 26 Exploring the Universe Chapter 26.3 LIFE CYCLES OF STARS

2. How Stars Form • Def: a nebula is a large cloud of gas and dust spread out over a large volume of space • Stars form in the densest regions of nebulae and are created by gravity

3. Nebulae • As the nebula contracts, it heats up, producing a shrinking cloud and gas and dust with enough mass to form a star called a protostar • A star is formed when a shrinking cloud of gas and dust becomes so dense and hot that nuclear fusion begins

4. Formation of Stars https://image.slidesharecdn.com/chapter9starsandgalaxies-140408230052-phpapp01/95/form-3-chapter-9-stars-and-galaxies-12-638.jpg?cb=1396998100

5. The Main Sequence of a Star (Mass) • A star’s mass: • determines the star’s place on the main sequence and how long it will stay there • Mass is determined by the amount of gas and dust available • The most massive stars have the most energy • High mass: • produce bright blue stars • use up their fuel quickly • last only a few million years http://s4.thingpic.com/images/6Y/GFShu79m3SFb3Mw24Y7pNoiG.jpeg

6. Main Sequence Star Diagram • Absolute magnitude: this is a scale that astronomers use ensure at standard scale is used when determining the characteristics of stars. http://phillips.seti.org/kids/images/definitions/hertzsprung-russell-diagram.png

7. Fuel For Stars • The fuel is hydrogen and helium which is converted to energy by nuclear fusion producing heavier elements • Middle-sized yellow stars like the sun remain stable for about 10 billion years • Our sun is estimated to be in its prime life at about 4.6 billion years • Small, cool red stars are long-lived for more than 100 billion years since they use their fuel slowly

8. So, what happens when the core runs out of hydrogen? • Star begins to collapse, heats up • Core contains He, continues to collapse • But H fuses to He in shell– greatly inflating star •  RED GIANT (low mass) • or SUPERGIANT (high mass)

9. What happens next depends on stellar mass http://web.pdx.edu/~ruzickaa/meteorites/stellarevol&nucleosynthesis.ppt

10. Running Out of Fuel…the Death Star? • When stars run out of fuel in the core (hydrogen and helium for nuclear fusion reactions) the star dies • Depending on the star’s mass dead stars will be: • a white dwarf, • neutron star, or • black hole • Low and medium mass stars (red and yellow) can be up to eight times as massive as our sun

11. Life Cycle of Star • The life cycle of stars depends on the mass of the star

12. Life Cycle of Low-Medium Mass Star • nebula: protostar: main sequence star: red giant: planetary nebula: white dwarf http://slideplayer.com/slide/10416117/35/images/3/Life+Cycle+of+Small+&+Medium+Mass+Stars.jpg

13. Red Giant • As quantity of hydrogen dwindles, gravity becomes stronger than pressure & core shrinks • Core temperature rises causing the hydrogen outside the shell to begin fusion • Energy flows outward making the star expand & atmosphere cooling in the outer regions causes the star to glow red • Def: a red giant is a large reddish star late in its life cycle that fuses helium into carbon or oxygen http://www.antonine-education.com/Image_library/Physics_5_Options/Astrophysics/giant.gif

14. Planetary Nebula • Red Giants can lose its outer layers—ultimately a planetary nebula forms, • leaving a white dwarf in the center • With decreasing energy from the core and less outward pressure to support the star against gravity’s inward pull, the star collapses producing a glowing cloud of gas (nebula) • Def: a planetary nebula is the glowing cloud of gas produced by a dying star Planetary nebula White dwarf http://web.pdx.edu/~ruzickaa/meteorites/stellarevol&nucleosynthesis.ppt

15. White Dwarf • The star blows off most of its mass leaving only its hot core • Def: A white dwarf is a very dense star that remains after the fusion in a red giant stops and the star will die • The white dwarf cannot fuse and cools slowly for an estimated 20 billion years (longer than the current age of the universe) • Our sun will end its life as a white dwarf http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit3/Images/nstar.gif

16. High Mass Stars

17. Life Cycle of High Mass Star • High mass stars have mass greater than eight times that of our sun • Their early life and main sequence are similar to low and medium mass stars • For high mass stars: nebula: protostar: main sequence: red supergiant: supernova: neutron star or black hole http://linus.highpoint.edu/~mdewitt/phy1050/images/week5/high-mass-cycle.jpg

18. RED SUPER GIANT • As high mass stars start to die, they become red supergiants • Def: red supergiants are extremely large stars that create elements as heavy as iron • As gravity overcomes pressure in massive stars, the collapse is dramatic creating a supernova • Def: A supernova is a powerful explosion that occurs when a massive star dies • The explosion can create elements heavier then iron https://dangthatscool.files.wordpress.com/2009/07/stardiagram3.jpg

19. Supernovae • The elements get ejected into space eventually becoming part of other solar systems (like ours) • The iron that exists on Earth came from supernovae that occurred billions of years ago https://www.youtube.com/watch?v=aysiMbgml5g http://www.dailygalaxy.com/.a/6a00d8341bf7f753ef01b8d2762be6970c-pi

20. End for high mass star comes as it tries to fuse core Fe into heavier elements– and finds this absorbs energy STAR COLLAPSES & EXPLODES AS SUPERNOVA and the elements created spread out from the explosion http://web.pdx.edu/~ruzickaa/meteorites/stellarevol&nucleosynthesis.ppt

21. Neutron Star • If the mass after the supernova is less than three times the sun’s mass, the star will die as a neutron star • Def: A neutron star is a dead star with the density of atomic nuclei • Neutron stars are only a few kilometers in diameter but so dense that they are sometimes detected as pulsars • Def: Pulsars are rapidly rotating sources of radio waves given off by rapidly rotating neutron stars https://d2gne97vdumgn3.cloudfront.net/api/file/c2EBRQFcQBi501EfaQqU

22. Black Holes • Def: A black hole is an object so massive that not even light can escape its gravity • Black holes are observed indirectly (since no light escapes) by gravitational influence of objects around them https://upload.wikimedia.org/wikipedia/commons/thumb/d/d6/BlackHole_Lensing.gif/290px-BlackHole_Lensing.gif

23. Nucleosynthesis: • Nucleosynthesis: formation of elements • Except for H, He (created in Big Bang), all other elements created by fusion processes in stars •  Stars are said to evolve with changes in the abundances of the elements within https://helios.gsfc.nasa.gov/onion.gif

24. Summary of nucleosynthesis processes http://web.pdx.edu/~ruzickaa/meteorites/stellarevol&nucleosynthesis.ppt

25. Hydrogen Carbon oxygen Neon through Iron Many heavy elements Hydrogen