1 / 61

Schedule

Astronomy 100 Tuesday, Thursday 2:30 - 3:45 pm Tom Burbine tburbine@mtholyoke.edu www.xanga.com/astronomy100. Schedule. Today – Class Tuesday-Class Wednesday- Review Session Hasbrouck 134 from 7-8 pm Thursday-Exam #3 (Chapters 15, 16, 17, 18). Homework Assignment (Due Today).

yvonne
Télécharger la présentation

Schedule

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Astronomy 100Tuesday, Thursday 2:30 - 3:45 pmTom Burbinetburbine@mtholyoke.eduwww.xanga.com/astronomy100

  2. Schedule • Today – Class • Tuesday-Class • Wednesday- Review Session • Hasbrouck 134 from 7-8 pm • Thursday-Exam #3 (Chapters 15, 16, 17, 18)

  3. Homework Assignment(Due Today) • Make up a test question • Multiple Choice • A-E possible answers • 1 point for handing it in • 1 point for me using it on test • The question needs to be on material that will be on the 3rd exam • 15 people got extra HW credit for me using their question (or inspiring a question)

  4. OWL assignment (Due Today) • There is be an OWL assignment due on Thursday March 31 at 11:59 pm. • There are 15 questions and a perfect score will give you 2 homework points.

  5. OWL assignment (Due Tuesday) • There is be an OWL assignment due on Tuesday April 5 at 11:59 pm. • There are 15 questions and a perfect score will give you 2 homework points.

  6. Things to remember • 90% of classified stars are on main sequence • Main sequence stars are “young” stars • If a star is leaving the main sequence, it is at the end of its lifespan of burning hydrogen into helium

  7. Remember • Largest stars on main sequence are O stars • Largest stars that can exist are supergiants

  8. You need to know stellar classifications • O, B, A, F, G, K, M • A0, A1, A2, … A9 in the order from the hottest to the coolest

  9. wd white dwarfs

  10. Classifications • Sun is a G2 V • Betelgeuse is a M2 I • Vega is a A0 V • Sirius is a A1 V • Arcturus is a K3 III

  11. Binaries • About half of stars orbit a companion • 3 classes of binaries

  12. Visual Binary • We can see the stars rotating around each other with a telescope

  13. Eclipsing Binary The light from a star system drops as a star goes in front and behind another star.

  14. Spectroscopic Binary The spectral lines of a star can be seen to be moving to shorter wavelengths and also to longer wavelengths

  15. Importance of Binaries • It allows you to possibly determine a star’s mass if you know the orbital period and the separation of the two stars

  16. Life of a Star • A star-forming cloud is called a molecular cloud because low temperatures allow Hydrogen to form Hydrogen molecules (H2) • Temperatures like 10-30 K • Denser than surrounding regions

  17. Region is approximately 50 light years across

  18. Condensing • Molecular clouds tends to be lumpy • These lumps tend to condense into stars • That is why stars tend to be found in clusters

  19. Protostar • The dense cloud fragment gets hotter as it contracts • The cloud becomes denser and radiation cannot escape • The thermal pressure and gas temperature start to rise and rise • The dense cloud fragment becomes a protostar

  20. When does a protostar become a star • When the core temperatures reaches 10 million K, hydrogen fusion can start occurring

  21. 3 Basic Groups of Stars • Low-mass stars – born with less than 2 Solar Masses • Intermediate-mass stars – born between 2 and 8 solar masses • High-mass stars – born with masses greater than 8 solar masses

  22. Things you need to know • Fusion rate increases with increasing temperature • There is a relation between thermal pressure and gravity

  23. Animation • Death sequence of the Sun

  24. Sun ends it time on the main sequence • When the core hydrogen is depleted, nuclear fusion stops • The core pressure can no longer resist the crush of gravity • Core shrinks

  25. Why does the star expand? • The core is made of helium • The surrounding layers are made of hydrogen

  26. And .. • Gravity shrinks the inert helium core and surrounding shell of hydrogen • The shell of hydrogen becomes hot for fusion • This is called hydrogen-shell burning

  27. And … • The shell becomes so hot that its fusion rate is higher than the original core • This energy can not be transported fast enough to surface • Thermal pressure builds up and the star expands

  28. And .. • More helium is being created • Mass of core increases • Increases its gravitational pull • Increasing the density and pressure of this region

  29. When • When helium core reaches 100 million Kelvin, • Helium can fuse into a Carbon nucleus

  30. Helium Flash • The rising temperature in the core causes the helium fusion rate to rocket upward • Creates a lot of new energy

  31. However • The core expands • Which pushes the hydrogen-burning shell outwards • Lowering the hydrogen-burning shell’s temperature

  32. And • Less energy is produced • Star starts to contract

  33. Now • In the core, Helium becomes Carbon • Star contracts • Helium fusion occurs in a shell surrounding the carbon core • Hydrogen shell can fuse above the Helium shell • Inner regions become hotter • Star expands

  34. Can Carbon undergo fusion? • Yes, but can’t reach the needed temperature (600 million Kelvin) in a low-mass star • Carbon on Earth is produced in the cores of stars

  35. Planetary Nebulae • There is a carbon core and outer layers are ejected into space • The core is still hot and that ionizes the expanding gas

  36. Planetary Nebulae

  37. White Dwarf • The remaining core becomes a white dwarf

  38. PRS Question • At the end of the Sun’s lifespan when it becomes a white dwarf, the white dwarf will be mostly composed of • A) Hydrogen • B) Helium • C) Carbon • D) Oxygen • E) Iron

  39. PRS Question • At the end of the Sun’s lifespan and it becomes a white dwarf, the white dwarf will be mostly composed of • A) Hydrogen • B) Helium • C) Carbon • D) Oxygen • E) Iron

  40. High-Mass Stars • The importance of high-mass stars is that they make elements heavier than carbon • You need really hot temperatures which only occur with the weight of a very high-mass star

  41. Stages of High-Mass Star’s Life • Similar to low-mass star’s • Except a high-mass star can continue to fuse elements • When the fusion ceases, the star becomes a supernova • Supernova is a huge explosion

More Related