Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 1 Announcements: Exam #3: May 3 (Chp 12, 13)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 2 HR Diagram of the Brightest Stars

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5 Conclusions: Low mass stars are more common in our galaxy (not a lot of O and B-type Main Sequence Stars in the HR Diagram of the closest stars). Stars spend most of their time on the Main Sequence (not a lot of supergiants and giants in the HR Diagram of the closest stars).

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 6 Chapter 13

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7 Introduction Where do stars come from? Giant Molecular Clouds Bok Globules Interstellar Medium (ISM) Protostars Pre-Main Sequence Stars How do they age (evolve) What is their fate?

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 8 Bi-polar jets Herbig-Haro objects (HH objects) Brown Dwarfs Contraction timescales depend on mass Hydrostatic Equilibrium

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 11 Planetary Nebulae: Typical size: 0.25 ly Typical velocity of expanding material: 20 km/s

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 12 At the end of its life, a star like the Sun will shed its outer layers.

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 14 Collapse of Massive Stars: As the star’s core shrinks, protons and electrons merge to form As the star’s core shrinks, protons and electrons merge to form neutrons and the core is transformed into a sphere of neutrons. neutrons and the core is transformed into a sphere of neutrons. p + + e -  n + p + + e -  n + The loss of electrons in the creation of the neutrons causes the The loss of electrons in the creation of the neutrons causes the core pressure to drop suddenly – nothing remains to support the core pressure to drop suddenly – nothing remains to support the star, so its inner layers collapse star, so its inner layers collapse In a matter of seconds the Earth-sized iron core is transformed into a 10-km, extremely dense ball of neutrons

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 15 Collapse of Massive Stars: The outer layers of the star, now not supported as well, collapse The outer layers of the star, now not supported as well, collapse and heat to billions of degrees as they slam into the neutron and heat to billions of degrees as they slam into the neutron core. core. The gas pressure surges and thrusts the outer layers back into The gas pressure surges and thrusts the outer layers back into space in a gigantic explosion – a supernova. space in a gigantic explosion – a supernova.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 16 Supernova Explosions: In a few minutes, more energy is released than during the star’s In a few minutes, more energy is released than during the star’s entire life. entire life. It brightens to several billion times the luminosity of the Sun – It brightens to several billion times the luminosity of the Sun – a rate larger than all the stars in the Milky Way combined. a rate larger than all the stars in the Milky Way combined. Speeds may exceed 10,000 km/sec Speeds may exceed 10,000 km/sec Free neutrons from the explosion synthesize heavier Free neutrons from the explosion synthesize heavier elements (e.g., gold, platinum, uranium) elements (e.g., gold, platinum, uranium) Materials mix with interstellar matter to be recycled into a new Materials mix with interstellar matter to be recycled into a new generation of stars generation of stars

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 17 NGC 4725 (late 1940’s)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 18 Large Magellanic Cloud: SN1987A

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 20 Crab Nebula: Noted by Chinese Astronomers in 1054 AD Constellation of Taurus 6000 LY away 6 LY across Expanding at 3 million MPH

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 23 Stars like the Sun probably do not form iron cores during their evolution because a) all of the iron is ejected when they become planetary nebulae b) their cores never get hot enough for them to make iron by nucleosynthesis c) the iron they make by nucleosynthesis is all fused into carbon d) their strong magnetic fields keep their iron in the atmosphere e) none of the above