1 / 13

Summary of Post-Main-Sequence Evolution of Sun-Like Stars

0. Summary of Post-Main-Sequence Evolution of Sun-Like Stars. Core collapses; outer shells bounce off the hard surface of the degenerate C,O core. Formation of a Planetary Nebula. Fusion stops at formation of C,O core. C,O core becomes degenerate. M < 4 M sun. 0.

clarke-chan
Download Presentation

Summary of Post-Main-Sequence Evolution of Sun-Like Stars

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. 0 Summary of Post-Main-Sequence Evolution of Sun-Like Stars Core collapses; outer shells bounce off the hard surface of the degenerate C,O core Formation of a Planetary Nebula Fusion stops at formation of C,O core. C,O core becomes degenerate M < 4 Msun

  2. 0 The Remnants of Sun-Like Stars: White Dwarfs First example: Sirius B (Astrometric binary; discovered 1862) • M ≈ 1 M0 • L ≈ 0.03 L0 • Te ≈ 27,000 K • R ≈ 0.008 R0 • r ≈ 3x106 g/cm3

  3. 0 White Dwarfs Degenerate stellar remnant (C,O core) Extremely dense: 1 teaspoon of WD material: mass ≈ 16 tons!!! Chunk of WD material the size of a beach ball would outweigh an ocean liner! Central pressure: Pc ~ 3.8*1023 dynes/cm2 ~ 1.5x106 Pc,0 for Sirius B

  4. 0 Thin remaining surface layers of He and H produce absorption lines; DB (Broad He abs. lines) DA (Broad H abs. lines) (ZZ Ceti Variables; P ~ 100 – 1000 s) Low luminosity; high temperature => Lower left corner of the Herzsprung-Russell diagram.

  5. 0 Degenerate Matter Dx ~ n-1/3 Heisenberg Uncertainty Principle: (Dx)3 (Dp)3 ~ h3 => (Dp)3min ~ n h3 Non-degenerate matter (low density or high temperature): Number of available states Electron momentum distribution f(p) e-E(p)/kT Electron momentum p

  6. 0 Degenerate Matter Dx ~ n-1/3 Heisenberg Uncertainty Principle: (Dx)3 (Dp)3 ~ h3 => (Dp)3min ~ n h3 Degenerate matter (High density or low temperature): Fermi momentum pF = ħ (3p2ne)1/3 Electron momentum distribution f(p) e-E(p)/kT Number of available states Electron momentum p

  7. 0 Degeneracy of the Electron Gas in the Center of the Sun

  8. 0 The Chandrasekhar Limit The more massive a white dwarf, the smaller it is. RWD ~ MWD-1/3 => MWD VWD = const. (non-rel.) WDs with more than ~ 1.44 solar masses can not exist! Transition to relativistic degeneracy

  9. 0 Temperature and Degree of Degeneracy as a Function of Radius in a White Dwarf

  10. 0 Cooling Curve of a White Dwarf Nuclei settling in a crystalline structure, releasing excess potential energy

  11. 0 White Dwarfs in Binary Systems X-ray emission T ~ 106 K Binary consisting of WD + MS or Red Giant star => WD accretes matter from the companion Angular momentum conservation => accreted matter forms a disk, called accretion disk. Matter in the accretion disk heats up to ~ 1 million K => X-ray emission => “X-ray binary”.

  12. Nova Explosions Hydrogen accreted through the accretion disk accumulates on the surface of the WD • Very hot, dense layer of non-fusing hydrogen on the WD surface Nova Cygni 1975 • Explosive onset of H fusion • Nova explosion

  13. Recurrent Novae In many cases, the mass transfer cycle resumes after a nova explosion. T Pyxidis R Aquarii → Cycle of repeating explosions every few years – decades.

More Related