Astronomy 1020-H Stellar Astronomy Spring_2014 Day-27

1. Astronomy 1020-H Stellar Astronomy Spring_2014 Day-27

3. Course Announcements • SmartworksChapters 14: Due Mon. 3/31 • Smartworks Chapters 15: Due Mon. 3/31 • Exam-3: Mon. 3/31 – Chapters 13 (rest), 14, 15 • Dark Night – Mon. 3/31 at the Observatory

4. Astronomy in the Fall, 2014 Astr 1010 - Planetary Astronomy + Lab (H,R) Astr 1020 - Stellar Astronomy + Lab (R) Astr 2010 - Problems in Planet Astronomy Astr 2011 - Intro. to Observational Astronomy Astr 3005 - Observational Astronomy + Lab Astr 4010 – Intro. to Stellar Astrophysics Phys 3701 - Advanced Lab (this one will be astronomy based)

5. At lower temperatures, hydrogen is in single, neutral atoms. • This gas emits radio waves with  = 21 cm. • Light of this wavelength penetrates the dust. • Good for mapping the Milky Way.

6. Many clouds are cold enough for hydrogen to be in the H2 molecule. • These are called molecular clouds. • Dense and cold, and appear dark.

7. Temperatures are around 10 K, with densities as high as 1010 molecules/cm3. • Emit radio waves. • Many other molecules are in the mix.

8. Some clouds can have masses as large as 10 million times that of the Sun: giant molecular clouds. • On average, 120 light-years in size. • Stars form in these molecular clouds.

9. Molecular clouds are cold and dense. • Some places in the cloud are denser than average. • Self-gravity will make these regions collapse.

10. Rate of collapse is slowed by magnetic fields, turbulence, and angular momentum (spin). • Collapse and fragmentation lead to dense star-forming molecular-cloud cores. • The Sun began in one of these cores.

11. Molecular cores collapse under their own gravity. • Center shrinks fastest; outer layers later. • This produces a dense protostar.

12. Spin of core produces a disk of material around the protostar. • Material falls onto the growing protostar from the disk. • Our Solar System began this way.

13. The interstellar material that becomes stars and planets must have the key elements for life if those planets are going to have it. • Water and oxygen have been detected in some star-forming regions.

14. Concept Quiz—H II Regions In H II regions, the hydrogen gas is in what form? • doubly ionized hydrogen • once-ionized hydrogen • neutral hydrogen atoms • hydrogen molecules

15. Protostars • Protostars are large, cool, and luminous. • They will emit infrared light. • Infrared studies of molecular regions reveal protostars and their disks.

16. The protostar continues to accrete more material. • It continues to shrink and radiate away energy, balancing pressure and gravity. • The interior temperature and pressure rise.

17. MATH TOOLS 15.1 • The low temperature of dust means that it glows in the infrared. • 100 K dust: • 10 K dust:

18. The protostar’s energy source is gravitational energy. • As it shrinks, temperature rises in the core. • Hydrogen fusion begins in the core: It becomes a main sequence star.

19. The temperature in the core must be hot enough for fusion, 10 million K. • Very low-mass stars (< 0.08 M) never start hydrogen fusion. • These are called brown dwarfs.

20. Concept Quiz—Energy What is the source of energy for a protostar on the Hayashi track? • hydrogen fusion • bipolar jets • gravitational contraction • angular momentum

21. Evolutionary Tracks • An individual star follows an evolutionary track on the Hertzsprung-Russell diagram. • This is the path of the temperature and luminosity with time.

22. Evolutionary Tracks • Protostars get less luminous (for lower masses), smaller in radius, and hotter. • The star moves on the Hayashi track and arrives on the main sequence.

23. MATH TOOLS 15.2 • A lower-mass star like the Sun is more luminous as a protostar than as a main sequence star, even though it is cooler as a protostar. • This is due to its physical size (radius). 1,056

24. Concept Quiz—Evolutionary Tracks Once fusion begins, a star moves to the left on the H-R diagram. Its luminosity does not change, but its temperature rises. The star is • expanding. • contracting. • staying at the same radius. • can’t tell from the information given

25. The more massive the protostar, the more rapidly it evolves

26. Concept Quiz Evolutionary Tracks • Once fusion begins, a star moves to the left on the H-R diagram. Its luminosity does not change, but its temperature rises. The star is: • Expanding. • Contracting. • Staying at the same radius. • Can’t tell from the information given.

27. Many or all protostars have material leaving in a bipolar outflow of jets. • Infalling and outflowing gas can be very complex.

28. Bipolar Outflows • Powerful jets can collide with the interstellar medium to make Herbig-Haro (HH) objects. • These can eject muchof the mass that would otherwise land on the star.

29. Star formation can make star clusters. • These are gravitationally bound groups of stars. • Clusters are good laboratories for testing our ideas of star formation and evolution.

30. Star formation may take millions of years. • Some stars are more massive; others less so. • Higher-mass stars take less time forming and evolving.

33. Star Clusters • All stars are: • - same age • - same composition • same distance • Only difference: • -mass

34. PROCESS OF SCIENCE • New investigative methods can reveal misunderstandings. • Astronomers did not realize the presence and effect of gas and dust on starlight until spectroscopy was developed and applied.

35. CONNECTIONS 15.1 • A brown dwarf is not a star, nor a planet, but is in between. • Classified as L, T, or Y (cooler than M stars). • Glow in the infrared due to internal heat from gravitational contraction. • Over 1,000 have been found since the mid-1990s.