1 / 21

Annoucements

Dive into the journey of stars, from protostars collapsing under gravity to the fate of the Sun as a red giant. Explore topics like luminosity, temperature, and the evolving structure of stars. Learn about the vibrant process of nuclear fusion and the fascinating Helium Flash phenomenon.

judsonc
Download Presentation

Annoucements

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. Annoucements • Go observing! Soon! • The next exam is on Friday, October 8. • That is only 9 days from today.

  2. How Stars Evolve • Evolution of protostars onto main sequence • Gravitational contraction • Luminosity versus temperature and radius • The fate of the Sun • Red giant phase • Helium flash • Reading: sections 19.4, 18.4, 19.1

  3. Protostars evolve into main-sequence stars Hotter

  4. Protostars evolve into main-sequence stars • Protostar collapses under gravity. • The collapse releases energy. • The star is relatively transparent, so the energy is radiated away, temperature doesn’t change much. • The star gets smaller so it get dimmer. Brighter Hotter

  5. Luminosity versus radius and temperature 2 1 R = RSun T = TSun R = 2 RSun T = TSun Which star is more luminous?

  6. Luminosity versus radius and temperature 2 1 R = RSun T = TSun R = 2 RSun T = TSun • Each cm2 of each surface emits the same amount of radiation. • The larger stars emits more radiation because it has a larger surface. It emits 4 times as much radiation.

  7. Luminosity versus radius and temperature 1 2 1 R = RSun T = TSun R = RSun T = 2TSun Which star is more luminous? The hotter star is more luminous. Luminosity varies as T4 (Stefan-Boltzmann Law)

  8. Luminosity Law L R2T4 Luminosity surface area  (Radius)2 Luminosity (Temperature)4 2 1 If star A is 2 times as hot as star B, and the same radius, then it will be 24 = 16 times as luminous.

  9. Protostars evolve into main-sequence stars • The star gets smaller so it get dimmer. • Next the protostar becomes opaque, light no longer escapes easily. • Heat is trapped and the protostar gets hotter. • Finally, the core gets hot enough to start nuclear fusion, contraction stops. Brighter Hotter

  10. More massive protostars evolve faster

  11. Choose the best match: All ____stars have ___ than ___ stars. • Main-sequence : more mass : pre-main sequence • More massive : shorter lifetimes : less massive • More luminous : larger radii : less luminous • Holllywood : worse tans : Broadway

  12. The Fate of the Sun • How will the Sun evolve over time? • What will be its eventual fate?

  13. Sun’s Structure • Core • Where nuclear fusion occurs • Envelope • Supplies gravity to keep core hot and dense

  14. Main Sequence Evolution • Core starts with same fraction of hydrogen as whole star • Fusion changes H  He • Core gradually shrinks and Sun gets hotter and more luminous

  15. Gradual change in size of Sun Now 40% brighter, 6% larger, 5% hotter

  16. Main Sequence Evolution • Fusion changes H  He • Core depletes of H • Eventually there is not enough H to maintain energy generation in the core • Core starts to collapse

  17. Red Giant Phase • He core • No nuclear fusion • Gravitational contraction produces energy • H layer • Nuclear fusion • Envelope • Expands because of increased energy production • Cools because of increased surface area

  18. Sun’s Red Giant Phase

  19. HR diagram Giant phase is when core has been fully converted to Helium

  20. Helium Flash • He core • Eventually the core gets hot enough to fuse Helium into Carbon. • This causes the temperature to increase rapidly to 300 million K and there’s a sudden flash when a large part of the Helium gets burned all at once. • We don’t see this flash because it’s buried inside the Sun. • H layer • Envelope

  21. Movement on HR diagram

More Related