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Exploding stars

Exploding stars. László Kiss, School of Physics, University of Sydney. 1572: Tycho Brahe discovered a new star in Cassiopeia. “De nova stella...” (“About a new star...”). ...which faded away after a year. Today a hot gas cloud is visible there (mostly in X-rays). (Chandra).

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Exploding stars

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  1. Exploding stars László Kiss, School of Physics, University of Sydney

  2. 1572: Tycho Brahe discovered a new star in Cassiopeia...

  3. “De nova stella...” (“About a new star...”)

  4. ...which faded away after a year. Today a hot gas cloud is visible there (mostly in X-rays). (Chandra)

  5. See also: ancient “guest stars” in Chinese, Korean and Japanese chronicles AD 1006 AD 185 AD 1181 AD 1054

  6. The zoo of close binary stars

  7. Cataclysmic variable stars: interacting semidetached binaries with an accretion disk

  8. (Keele University)

  9. Three types of “novae” • dwarf novaeaccretion disk instability, no thermonuclear reactions, repetitive process (5-5,000 days) • classical novaethermonuclear runaway on the white dwarf's surface, repetitive process (10-10,000 years) • (Type Ia) supernovaeirreversible destruction of the white dwarf (Chandra PR)

  10. Dwarf novae: no real explosion (U Gem, J. Blackwell)

  11. Accretion disk instability... ...driven by the hydrogen ionization at 10,000 K

  12. The light curve of RX And (1974-2000)

  13. Classical novae: “new” stars never noticed before • outburst amplitude: 7-12 mag (V1500 Cyg: >20 mag!) • rapid fading after maximum (speed classes using tn) • absolute magnitudes in maximum: -7 ... -10 mag • MV ~ an+bn log tn (n=2, 3)

  14. Discovery: a task for amateur astronomers (APOD)

  15. Like Nova Cygni 2001/2 (V2275 Cyg)...

  16. “A spectrum is worth thousand light curves...”

  17. E.g.: the existence of an accretion disk in dwarf novae

  18. Confirmation: by spectroscopy A spectrum tells the difference • dwarf nova in outburst?H lines in absorption (thick accrection disk) • new nova?H, He, Fe, ... lines in emission (ejected gas cloud) • new (Ia) supernova?no hydrogen lines, few broad features

  19. Expansion kinematics: the P Cygni profile (Carroll & Ostlie 1996)

  20. V5115 Sgr (Nova Sgr 2005)

  21. Late spectra: geometry of the shell (Gill & O'Brien, 1999, MNRAS, 307, 677)

  22. Like V1494 Aql (Nova Aql 1999/2), 5 years later:

  23. Novae and distances: expansion parallax GK Per (Nova Per 1901) First approximation: d=vexp (t-t0)/

  24. Supernovae: stars that can outshine a whole galaxy! (HST)

  25. (SNe 1999el and 2000E)

  26. Types of supernovae (simplified)

  27. The nearest and brightest since 1604: SN 1987A in the Large Magellanic Cloud

  28. “Light echoes”: light scattered by interstellar dust clouds

  29. System geometry (P. Garnavich)

  30. “The Lord of the Rings”: gas rings around SN 1987A, ejected by the progenitor (HST)

  31. Types of supernovae (simplified)

  32. The expansion of the Universe is accelerating!

  33. Brian Schmidt ANU, Canberra

  34. Even bigger explosions: • Hypernovae: very massive Type II SNe, thought to produce 100x more energy than “regular” SNe • Gamma Ray Bursts (GRBs): rapid flashes across the electromagnetic spectrum. Massive stars collapsing to black holes (related to hypernovae); binary mergers (e.g. two neutron stars collapsing into a black hole) ...and the story goes on

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