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Phys 1830: Lecture 31

Phys 1830: Lecture 31. Shapely 1, Malin. SNR G21.5-0.9 Bietenholz, Mathewson, Safi-Harb. Office Hour Today 3pm Allen 514. Extra Image-making workshop! April 8, 5:30pm, Allen 536(?). Previous Classes: Stellar Evolution of a 1 solar mass star Radii, Mass, Lifetime on Main Sequence

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Phys 1830: Lecture 31

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  1. Phys 1830: Lecture 31 Shapely 1, Malin SNR G21.5-0.9 Bietenholz, Mathewson, Safi-Harb Office Hour Today 3pm Allen 514 Extra Image-making workshop! April 8, 5:30pm, Allen 536(?) • Previous Classes: • Stellar Evolution of a 1 solar mass star • Radii, Mass, Lifetime on Main Sequence • This class: • Stellar Evolution of a 1 solar mass star • Stellar Evolution: more massive stars • Supernovae Type II • Upcoming classes • black holes • Galaxies • Cosmololgy

  2. Star Formation: • Note the jet coming out of the molecular cloud. Bok Globule

  3. Star Formation and the H-R Diagram: ALMA proplyd • Large, cool protostar in the centre of proplyd nebula  in upper right. • Protostar contracts and temperature increases. • Fusion in core  on the Main Sequence.

  4. Star Formation and the H-R Diagram: ZAMS • Zero Age Main Sequence at left edge of MS. • Stars live on MS for millions to billions of years. • Evolve off of MS when H in core is converted to Helium.

  5. Star Formation and the H-R Diagram: MS Brown Dwarfs • Brown dwarfs are stars that • have small enough masses that they do not initiate nuclear fusion of H • do not reside on the MS

  6. Stellar Evolution and the H-R Diagram: • Evolution of a 1 solar mass star. • Post-MS Main Stages: • Red Giant • Planetary Nebula • White Dwarf

  7. Red Giant Stage: Antares • Radius increases and surface temperature decreases. Almost as large as the orbit of Jupiter. • Fusion of He in core into Carbon (C) is initiated. • From MS to PN stage is roughly 10**8 years.

  8. Planetary Nebula Model • Outer envelope of star is ejected. • Core of star is revealed. • Hot core ionizes the expanding envelope.

  9. HST/WFC3

  10. The Eskimo Nebula: Masking used to superimpose bright and faint structures.

  11. Planetary Nebula Stage: • Lasts ~ 3 * 10**4 yrs. • Radius 0.25 to 2 ly.

  12. White Dwarf: HST Binary system of Sirius A and Sirius B • E.g. Sirius B (Bond et al.). Dot in left corner. • High T, low L  R very small (e.g. size of Earth). • The stellar core after the nebula has dissipated.

  13. White Dwarf Stage: HST Binary system of Sirius A and Sirius B • Contracts until it becomes a Degenerate Electron Gas: electrons packed as tightly as they can be. • Pressure support since negative charges repulse each other. • Fades over 100s * 10**9 yrs.

  14. Stellar Evolution of a 1 solar mass star: • The position of a star on the HR diagram changes as the star evolves.

  15. A planetary nebula is a) a contracting spherical cloud of gas surrounding a newly formed star, in which planets are forming. b) the expanding nebula formed by the supernova explosion of a massive star. c) an expanding gas shell surrounding a hot, white dwarf star. d) a disk-shaped nebula of dust and gas from which planets will eventually form, easily photographed around relatively young stars.

  16. Do as exercise outside of class What does the star look like at that stage? What processes are occurring? Where is it on the HR diagram? • Describe to your neighbour the 5 main stages of evolution for a star like our sun, starting with star birth.

  17. At which stage does material flow from a star for a 100 million years? • Main Sequence • Planetary Nebula • Giant Star • White Dwarf

  18. Star Death – larger masses SNR G21.5-0.9 Bietenholz, Mathewson, Safi-Harb Radio data assigned blue; X-ray data assigned red. Supernova Remnants and Exotic Stars.

  19. Supernovae Type Ia – Scenario 1

  20. Supernovae Type Ia – Scenario 1 • Recall that most stars are in binary star systems. • Perhaps one will evolve a bit faster than the other star.  a giant and a white dwarf. • Tenuous outer material from the giant star falls onto the white dwarf. • Limit to the amount of mass that a white dwarf can support Chandrasekhar limit ~ 1.4 solar masses.

  21. Supernovae Type Ia • Exceeding the Chandrasekhar limit results in a runaway fusion process that blasts the white dwarf apart, totally destroying it.

  22. Supernovae Type Ia – Scenario 2

  23. Supernovae Type Ia – Scenario 2 • Recall that most stars are in binary star systems. • Two white dwarfs. • Merge together. • Limit to the amount of mass that a white dwarf can support Chandrasekhar limit ~ 1.4 solar masses.

  24. Supernovae Type Ia – Scenario 2 • Exceeds Chandrasekhar limit  explosion

  25. Supernovae Type Ia – Result • Supernova Remnant (SNR) without a giant star near the centre.

  26. Supernovae Type Ia • ~1.4 solar masses converts to a small range of possible energies  a small range of intrinsic luminosity. Which particular luminosity, within this range, can be determined from the shape of the light curve. • Use the Inverse Square Brightness Law to get the distance to the galaxy hosting the explosion.

  27. Supernovae Type Ia • Using these very bright explosions  the distance to galaxies very far away. (e.g. galaxies in the Hubble Deep Field) • What can we get from knowing the distance?.

  28. Big Bang: The Expansion of the Universe: Observations The expansion is accelerating! • Plot the distance determined from SNe versus the velocity (redshift = v/c) of the host galaxy determined from spectral observations of the Doppler shift. • Can assess this for an understanding of Dark Energy.

  29. Big Bang: The Expansion of the Universe: Observations The expansion is accelerating! • What does this mean for the fate of the universe?

  30. Stellar Evolution: • White clouds are dust (IR) + plasma (radio)  where stars are forming. • Yellow to red spherical objects are plasma (radio)  SNe remnants.

  31. Stellar Evolution and the H-R Diagram: • A massive star: focus on M > ~8 -12 solar masses. • Travel back and forth across the top of the HR diagram.

  32. Supernovae Type II • Core-collapse supernovae. • Core progressively fuses elements including Iron. • However the fusion of iron requires energy so doesn't provide a supporting outward pressure to balance inward pull of gravity.

  33. Supernovae Type II • Core collapses -> implosion. • protons and electrons are crushed together forming neutrons. • Degenerate gas of packed neutrons. • Infalling material hits this dense core and bounces outwards. -> outward moving shockwave. • blasts the outermost layers of the star into space at nearly the speed of light.

  34. Supernovae Type II Crab Nebula: Malin, HST, Chandra • Supernova explosion: • Supernova remnant (SNR) • Radii about 5 ly. • Core (neutron star, black hole, or nothing)

  35. Review: • Describe to your neighbour 2 different ways of creating supernovae.

  36. Supernovae SN Type Ia SN Type II • SN Type Ia: • White Dwarf (WD) stars involved and detonation at the Chandrasekhar limit. • WD accumulates mass from a companion star • merger of 2 WDs • SN Type II • Core collapse of a massive star.

  37. Supernovae Type II Heart of the Crab Nebula Lower star of the pair just left of centre. • Neutron star • ~ 10 km radius • Electron crust surrounding neutron degenerate gas. • High magnetic field • Conservation of angular momentum  rapid rotation.

  38. Supernovae Type II • Pulsar • Electrons on surface are accelerated by magnetic field and jettisoned along magnetic poles  synchrotron emission. • If beam is not perpendicular to our line of sight then we see a pulsar. • The disk with the beam in turquoise is a Pulsar Wind Nebula at x-ray wavelengths.

  39. Review: All though all pulsars are neutron stars, not all neutron stars are pulsars. One of the reasons is that in order to be categorized as a pulsar the neutron star's beam of electromagnetic radiation must be oriented in the direction of Earth. If instead the beam is oriented perpendicular to our line of sight then we do not see the pulses and it is not categorized as a pulsar. This is one of the reasons why some supernova remnants do not contain pulsars. a) True b) False

  40. Crab Nebula Movie • Left is x-ray. Right is visual. • Pulses 30 times a second. • Formed in 1054 A.D.

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