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)
See also: ancient “guest stars” in Chinese, Korean and Japanese chronicles AD 1006 AD 1054 AD 185 AD 1181
The zoo of close binary stars
Cataclysmic variable stars: interacting semidetached binaries with an accretion disk
(Keele University)
Three types of “novae” dwarf novae accretion disk instability, no thermonuclear reactions, repetitive process (5-5,000 days) classical novae thermonuclear runaway on the white dwarf's surface, repetitive process (10-10,000 years) (Type Ia) supernovae irreversible destruction of the white dwarf (Chandra PR)
Dwarf novae: no real explosion (U Gem, J. Blackwell)
Accretion disk instability......driven by the hydrogen ionization at 10,000 K
The light curve of RX And ( )
Classical novae: “new” stars never noticed before outburst amplitude: 7-12 mag (V1500 Cyg: >20 mag!) rapid fading after maximum (speed classes using t n ) absolute magnitudes in maximum: mag M V ~ a n +b n log t n (n=2, 3)
Discovery: a task for amateur astronomers (APOD)
Like Nova Cygni 2001/2 (V2275 Cyg)...
“A spectrum is worth thousand light curves...”
E.g.: the existence of an accretion disk in dwarf novae
Confirmation: by spectroscopy 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 A spectrum tells the difference
Expansion kinematics: the P Cygni profile (Carroll & Ostlie 1996)
V5115 Sgr (Nova Sgr 2005)
Late spectra: geometry of the shell (Gill & O'Brien, 1999, MNRAS, 307, 677)
Like V1494 Aql (Nova Aql 1999/2), 5 years later:
Novae and distances: expansion parallax GK Per (Nova Per 1901) First approximation: d=v exp (t-t 0 )/
Supernovae: stars that can outshine a whole galaxy! (HST)
(SNe 1999el and 2000E)
Types of supernovae (simplified)
The nearest and brightest since 1604: SN 1987A in the Large Magellanic Cloud
“Light echoes”: light scattered by interstellar dust clouds
System geometry (P. Garnavich)
“The Lord of the Rings”: gas rings around SN 1987A, ejected by the progenitor (HST)
Types of supernovae (simplified)
The expansion of the Universe is accelerating!
Brian Schmidt ANU, Canberra
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