NATS 1880 Lecture Notes - Lecture 11: 51 Pegasi, Tidal Locking, Alpha Centauri
23 Jun 2018
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Lecture 11: Chapter 11 - Habitability Outside the Solar System
Learning Outcomes
- Describe the nature of stars, their basic properties and classiļ¬cation!
- Discriminate among the techniques used to discover extrasolar planets"
- Discuss what has been learned about extrasolar planets from observations!
- Explain why some scientists think life in the universe may be rare!
!
Important Questions!
1. What are the main spectral types for stars and their approximate temperatures?!
2. What are the three most eļ¬ective indirect techniques for discovering extrasolar
planets and explain brieļ¬y how each works?!
3. Why do some scientists think life may be rare in the universe?!
Chapter 11.1
-preferred place to look for habitable planets is around stars !
-necessary to investigate the nature of stars to continue our search for Life Beyond Earth !
-Eļ¬ect of Stellar Life Cycles:
-all stars form from the collapse of a large cloud of gas (largely H and He) !
-in a few million years, form either a!
-a) multiple star system (with/without planets), or!
-b) a single star with a planetary system !
-Interstellar Cloud (left) from which multiple stars (bottom left) and single stars with planetary
systems (bottom right) are formed. (Top image from Spitzer IR Space Telescope, bottom
images are artistsā conception.) !
-a protostar ļ¬rst forms, radiating heat due to the collapse of a gas cloud. !
-star is born when H begins to fuse to He in the core. !
-a star is a ball of gas powered by nuclear fusion and !
-held together by its own gravity. !
-stars spend 90% of their life fusing 4 H nuclei to one He nucleus + energy on the Main
Sequence. !
-when H has been used up in the core, the core contracts making it temporarily hotter. !
-the core becomes so hot that it can fuse He to Carbon (and later, heavier elements) !
-H can fuse to He in a shell outside the core causing the starās envelope to swell. !
-the star becomes a Red Giant or Red Supergiant star depending on its mass (10-15 Ć Sunās
mass ļø Supergiant). !
-stars like the Sun end up as a planetary nebula with a white dwarf at the centre. !
-stars much heavier than the Sun can fuse elements up to iron (in a series of shells) before
exploding in a supernova. !
-a supernova begins as a catastrophic collapse of the atmosphere of a large star onto a
superdense (iron) core. !
-in a supernova from a massive star, the atmosphere "bounces" on the super-dense iron core
and is expelled at thousands of km/s. !
-ā¢ The expelled material ā called the remnant ā is rich in heavy elements, including elements
heavier than iron which are made in the explosion, which ultimately mixes with nearby
interstellar gas from which the next generation of stars will form. !
-ā¢ The resulting core can be either a neutron star or a black hole. !
Document Summary
Lecture 11: chapter 11 - habitability outside the solar system. Describe the nature of stars, their basic properties and classi cation. Discriminate among the techniques used to discover extrasolar planets. Discuss what has been learned about extrasolar planets from observations. Explain why some scientists think life in the universe may be rare. Preferred place to look for habitable planets is around stars. Necessary to investigate the nature of stars to continue our search for life beyond earth. All stars form from the collapse of a large cloud of gas (largely h and he) In a few million years, form either a. A) multiple star system (with/without planets), or. B) a single star with a planetary system. Interstellar cloud (left) from which multiple stars (bottom left) and single stars with planetary systems (bottom right) are formed. (top image from spitzer ir space telescope, bottom images are artists" conception. )
