The Life Cycles of Stars. Dr. Jim Lochner, NASA/GSFC

Transcription

1 The Life Cycles of Stars Dr. Jim Lochner, NASA/GSFC

2 Twinkle, Twinkle, Little Star...

3 A constellation is an apparent group of stars originally named for mythical characters. The sky contains 88 constellations. The Constellation Orion

4 How I Wonder What You Are... Stars have Different colors Which indicate different temperatures The hotter a star is, the faster it burns its life away.

5 Magnitude (Brightness) Apparent magnitude is the brightness of a star when viewed from Earth. Three factors control the apparent brightness of a star as seen from Earth: how big it is, how hot it is, and how far away it is. Absolute magnitude is the apparent brightness of a star if it were viewed from a distance of 32.6 light-years. One light-year is 9.5 trillion kilometers or about 6 trillion miles.

6 Stellar Nursery Space is filled with the stuff to make stars.

7 Stars start from clouds Clouds provide the gas (Hydrogen) and dust from which stars form. But not this kind of dust Rather: Irregular Grains Of Carbon or Silicon

8 Collapse to Protostar Stars begin with slow accumulation of gas and dust. Gravitational attraction of Clumps attracts more material. Contraction causes Temperature and Pressure to slowly increase. When a protostar becomes hot enough for nuclear fusion to begin a star is born. F Gm 1 m 2 r 2

9 Nuclear Fusion! At 15 million degrees Celsius in the center of the star, fusion ignites! 4 ( 1 H) --> 4 He + 2 e neutrinos + energy Where does the energy come from? E = mc 2 Mass of four 1 H > Mass of one 4 He The energy is released by the sun as photons of light.

10 A Balancing Act Energy released from nuclear fusion counteracts inward force of gravity. Throughout its life, these two forces determine the stages of a star s life.

11 New Stars are not quiet! Expulsion of gas from a young binary star system

12 All Types of Stars Recall - Stars - Different colors indicate different temperatures

13 All Types of Stars Annie J Cannon ( ) Out Oh! Beyond Be Oh! a Fine Be Andromeda, a Girl Fine - Girl Kiss -Me Fiery Kiss Right Me Gases! Now Kindle Sweetheart Many Red! New Stars

14 Reprise: the Life Cycle Sun-like Stars Massive Stars

15 Life-cycle of Stars Sun-like Stars Massive Stars

16 H-R Diagram

17 A Red Giant You Know

18 The Beginning of the End: Red Giants After Hydrogen is exhausted in the core... Energy released from nuclear fusion counter-acts inward force of gravity. Core collapses, Kinetic energy of collapse converted into heat. This heat expands the outer layers. Meanwhile, as core collapses, Increasing Temperature and Pressure...

19 More Fusion! At 100 million degrees Celsius, Helium fuses: 3 ( 4 He) --> 12 C + energy (Produced at an intermediate step) (Only 7.3 MeV produced) Energy sustains the expanded outer layers of the Red Giant

20 The end for solar type stars After Helium is exhausted, outer layers of star are expelled. Planetary Nebulae

21 White dwarfs At center of Planetary Nebula lies a White Dwarf. Size of the Earth with Mass of the Sun A ton per teaspoon Inward force of gravity balanced by repulsive force of electrons.

22 Fate of high mass stars After Helium is exhausted, the core collapses again until it becomes hot enough to fuse Carbon into Magnesium or Oxygen. 12 C + 12 C --> 24 Mg or 12 C + 4 He --> 16 O Through a combination of processes, successively heavier elements are formed and burned.

23 Periodic Table Light Elements Heavy Elements 28 Si He 7( 3( 4 C O 4 ( He) 1 + H) C-N-O O C He Ni 20 C Cycle Ne Mg S O + energy + energy 56 Fe

24 The End of the Line for Massive Stars Massive stars burn a succession of elements. Iron is the most stable element and cannot be fused further. Instead of releasing energy, it uses energy.

25 Supernova!

26 Supernova Remnants: Cas A Optical X-ray

27 What s Left After the Supernova Neutron Star (If mass of core < 5 x Solar) Under collapse, protons and electrons combine to form neutrons. 10 Km across Black Hole (If mass of core > 5 x Solar) Not even compacted neutrons can support weight of very massive stars.

28 A whole new life: X-ray binaries In close binary systems, material flows from normal star to Neutron Star or Black Hole. X-rays emitted from disk of gas around Neutron Star/Black Hole.

29 Black Holes - Up Close and Personal Accretion Disk Event Horizon Singularity (deep in center) Jet (not always present)

30 SN interaction with ISM Supernovae compress gas and dust which lie between the stars. This gas is also enriched by the expelled material. This compression starts the collapse of gas and dust to form new stars.

31 Which Brings us Back to...

32 Materials for Life Cycles of Stars This presentation, and other materials on the Life Cycles of Stars, are available on the Imagine the Universe! web site at: