1 / 7

Detailed look at late stages of the Sun’s life:

Detailed look at late stages of the Sun’s life:. from Schr öder et al 2001 ( Astronomy & Geophysics Vol 42): radius of Sun as it ascends RGB, then AGB (with inner planet orbits marked!). but mass-loss in red-giant wind could be important: as is the likely temperature on Earth!.

tait
Télécharger la présentation

Detailed look at late stages of the Sun’s life:

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. Detailed look at late stages of the Sun’s life: • from Schröder et al 2001 (Astronomy & Geophysics Vol 42): • radius of Sun as it ascends RGB, then AGB (with inner planet orbits marked!) PHYS1005 – 2003/4

  2. but mass-loss in red-giant wind could be important: • as is the likely temperature on Earth! PHYS1005 – 2003/4

  3. Lecture 17: Stellar Structure and Evolution – II • Objectives: • Understand differences in evolution of low and high M stars • Importance of degeneracy pressure • Understand the Helium Flash H-R diagram showing evolutionary tracks followed by both young and old clusters: Note the gap between the Main Sequence and RGB in young clusters Additional reading: Kaufmann (chap. 21-22), Zeilik (chap. 16) PHYS1005 – 2003/4

  4. Evolution of 5MO Star: • on exhaustion of H in core (at 2) •  crisis point for high M stars • cores convective  well-mixed •  H runs out over large central volume at same time! •  must contract radically to ignite H shell • i.e. large change on thermal (short) timescale •  moves rapidly (23) to RGB • explains Hertzsprung Gap in young clusters • cf Low Mass stars: • cores are radiative  more stable  change much more gradual •  continuous and extended RGB in old clusters PHYS1005 – 2003/4

  5. Helium Flash and Degeneracy Pressure in low M stars • ignition of He at tip of RGB is crisis point for low M stars • due to new form of P which has been supporting the He core • comes from Pauli Exclusion Principle: • can estimate it as follows: • electron density of n per unit volume •  each electron occupies box of side • to avoid “overlap”, need de Broglie λ ~ size of box i.e. • therefore “degeneracy” energy • which is significant when Ed ~ kT i.e. • N.B. low m low n  electrons degenerate first! No two electrons within certain volume can occupy same quantum state • which links v and n (m = electron mass) PHYS1005 – 2003/4

  6. Electron degeneracy pressure • For case of ideal gas, where P = nkT • and since n αρ, then • which is independent of T ! • What happens when fusion begins in degenerate gas? • energy generated by fusion •  T rises •  fusion rate rises • but P stays the same  no expansion, no cooling ! • i.e. normal “safety valve” doesn’t work! •  disastrous runaway process until T very high • Helium Flash !L can rise to 1010 LO within ~ minutes PHYS1005 – 2003/4

  7. Evolutionary model for Sun: Binding Energy (first 31 elements) Speed of evolution: • evolution speeds up with age, because • L is higher (and timescale α M / L) • higher neutrino losses • less fusion energy from heavier elements • most stable nucleus is iron (56Fe) • H  Fe fusion converts 0.89% mass  energy, but • H  He fusion converts 0.71% ! • so later phases give little in total PHYS1005 – 2003/4

More Related