massive star death (SNe): Chapt 21 Lecture 22 – Stellar Evolution Star Fleet Academy Tues: Nov 4, 18, 25 Noon Alllen 326 Textbook on reserve at Science Library Read before class: Star Birth Chapt 18 and 19 Stellar Evolution M ~1 Msun (PN & WD): Chapt 20 massive star death (SNe): Chapt 21 stellar populations Chapt 23 (p. 587) Gamma-ray bursts & black holes Chapt 22 – REVIEW GR model of gravity ALL NOTES COPYRIGHT JAYANNE ENGLISH The state of the affairs from the previous class is that we measure arcs on the sky.

1. Star Formation – cold, dense dusty Molecular Clouds (MC): The bits of HII regions that are going to turn into proplyds are the dense, cold clouds. Horsehead Nebula Bok Globules

2. Star Formation (SF) in Cores in MC - Enhancements Green Bank Telescope, mm wavelengths https://public.nrao.edu/news/pressreleases/dust-grains-orion Credit: S. Schnee, et al.; B. Saxton, B. Kent (NRAO/AUI/NSF) Cores are knots in the filaments. 10 ly long dust filaments (orange) filled with pebbles protostars, in cores, may arise in nurturing environment for planets

2. Star Formation - Enhancements: Eagle Nebula (HST)

2. Star Formation - Enhancements: dense: Density ~ 10**6 atoms/cm**3 c.f. “space” ~1 atom/cm**3 …. c.f. sealevel 10**18 particles/cm**3 cold: T ~ 10K …. -263C Leads us back to the HR diagram Eagle Nebula. Evaporating Gaseous Globules (EGGs)

P causes dense clouds to gravitationally collapse & form stars. 3. SF - Enhancements collapse Balloon example. Kelvin-Helmholtz contraction. Conservation of Angular Momentum  disk-shaped cloud. P causes dense clouds to gravitationally collapse & form stars. forces: gravity & external P  self-gravity

4. Star Formation proplyds with protostars in centre Kelvin-Helmoltz contraction.

5. Star Formation: Nuclear Fusion Begins – bipolar outflow Protostar == first stage of becoming a star. Bipolar outflows: up to 15 ly radius (i.e. length of 1 jet) Some material from accretion disk shoots along polars at v > 10km/s … convert to hr as exercise Starts to clear system of gas and dust Late stage proto-star or early stage star: T Tauri stars. Herbig Haro Objects – bipolar outflows == jets emanating from protostars.

Note jet coming out of molecular cloud. Star Formation: Protostar buried in the molecular cloud. Note jet coming out of molecular cloud.

Star Formation: Herbig Haro Jets Radius 0.5 to 15 ly long! Moving at 10 km/s. How many km/hr?

Hot young stars  blue, massive Fusion in core  Zero Age MS 6. SF: Young stars The Pleiades . Hot young stars  blue, massive Fusion in core  Zero Age MS Still surrounded by dust reflecting blue light. group of stars with different masses.

Radiation & wind from O star  bubble in molecular cloud/ISM 6. SF: Young stars The Bubble Nebula by Bernard Michaud . Radiation & wind from O star  bubble in molecular cloud/ISM diameter 10 ly M ✪ > 45 M

This radio & FIR image shows: - clouds of heated dust where stars are forming (pink). - cold neutral hydrogen gas (diffuse structure) - the interstellar medium (ISM)

C A B Which image shows gas density enhancements that are about to collapse to form proto-stars? ________ Which image shows the stage of protostar formation?______ Which image is associated with the T Tauri or bipolar outflow stage? _______ Which image shows the stage where stars have nuclear fusion occuring in their cores? _______ D

SF on H-R Diagram : Hayashi Track L = 4 pi r**2 sigma T**4 100x larger than sun therefore L large K-H contraction  T increase so move left contraction  r decrease so L decrease For a star like our sun to form takes up to 50 million years. A higher mass star about 1 million years. A lower mass star about a billion years. Large, cool protostar in centre of proplyd nebula  in upper right. r contracts & T increases. Kelvin-Helmholtz Contraction. Fusion in core  on MS.

do not initiate nuclear fusion of H do not reside on the MS SF on H-R Diagram: MS Brown Dwarfs Recall the rogue planet or small star Nibiru from the Doomsday scenarios. Brown dwarf stars small enough masses do not initiate nuclear fusion of H do not reside on the MS

Evolve off of MS when H in core is converted to Helium (He). SF on H-R Diagram: ZAMS T~ 15*10**6K Zero Age Main Sequence (ZAMS) at left edge of MS with advent of nuclear fusion. Stars on MS Evolve off of MS when H in core is converted to Helium (He). MS is not an evolutionary track. Star in hydrostatic equilibrium i.e. P_outward = pull of gravity inward Thermal P: P from radiation + heat energy Tcore decrease  grav contraction  Tcore increase  Pout  radius So jiggles around a bit but stays on MS

Name/describe to your neighbour the 6 main stages of star birth like our sun.

STAR

Stellar Evolution: Star Death Recall Stefan-Boltzmann Law r == stellar radius T == surface temperature

H converted to He in core H burning in shell He not burning Leaving the MS H converted to He in core H burning in shell He not burning  no pressure P to counter gravity

Travels up the Red Giant Branch (i. e Travels up the Red Giant Branch (i.e. Subgiant Branch) of the HR diagram. Enriches ISM

What will happen? Part way through the evolution of 1 solar mass – see next lecture.