Cosmology & Stellar Evolution

Doppler Effect & Red Shift

  • Motion between observer and object changes detected wave frequency (sound or light)

  • Approaching: wavelength↓\text{wavelength} \downarrow → blue shift; Receding: wavelength↑\text{wavelength} \uparrow → red shift

  • Measurement of red shift allows estimation of object velocity & distance

Structure of the Universe

  • Sky mapped as huge filaments containing countless galaxies

  • Milky Way obscures central band of sky survey images

Big Bang Timeline (approx.)

  • 00: Big Bang – rapid expansion

  • 10−32 s10^{-32}\,\text{s}: Inflation driven by quantum fluctuations

  • 400,000 yr400{,}000\,\text{yr}: Afterglow light pattern (CMB); Universe enters Dark Ages

  • 4×108 yr4\times10^{8}\,\text{yr}: First stars ignite → galaxies form

  • 13.7 billion yr13.7\,\text{billion yr}: Present; Dark Energy causes accelerated expansion

Galaxy Morphology (Hubble Sequence)

  • Ellipticals: E0–E7E0–E7 (older, little gas)

  • Lenticulars: SOSO

  • Spirals: Sa,Sb,ScSa,Sb,Sc (increasingly open arms)

  • Barred Spirals: SBa,SBb,SBCSBa,SBb,SBC

  • Shape hints at galaxy age & interaction history

Stellar Energy & Fusion

  • Proton–proton chain: 4 1H→4He+energy (γ, e+, ν)4\,{}^1H \rightarrow {}^4He + \text{energy (}\gamma,\,e^+,\,\nu)

  • Fusion converts mass to energy, powering stars (Sun)

Star Formation

  • Giant molecular clouds collapse via gravity

  • Core heats; when T≈107 KT \approx 10^7\,\text{K}, hydrogen fusion starts → main-sequence star

Stellar Life Cycle & Supernovae

  • Massive stars fuse heavier elements up to FeFe

  • Core collapse supernova disperses elements; produces nebulae (e.g., Crab Nebula, observed 1054)

  • Supernova nucleosynthesis creates most elements >HeHe — basis for planets & life ("star stuff")

Black Holes

  • End state of very massive stars; gravity so strong that vescape>cv_{escape} > c

  • Defined by event horizon; no light escapes

Key Terms

  • Doppler Effect / Red Shift

  • Spectrum (light)

  • Galaxy types

  • Big Bang

  • Hydrogen, Helium

  • Fusion

  • Supernova

  • Black Hole