Exploding stars

László Kiss, School of Physics, University of Sydney

1572: Tycho Brahediscovered a newstar 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 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)

Dwarf novae: no real explosion

(U Gem, J. Blackwell)

Accretion disk instability...

...driven by the hydrogenionization at 10,000 K

The light curve of RX And (1974-2000)

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)

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=vexp (t-t0)/

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”: lightscattered by interstellardust 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 SchmidtANU, 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