Chapter 10: The Death of Stars (part b) The evolution of low-mass vs. that of high-mass stars. Planetary nebulae and the formation of white dwarf stars. Supernova explosions: two types Type I: due to “carbon detonation” of an accreting white dwarf in a binary. Type II: due to “core collapse” in a high-mass star. Both types of supernovae leave behind remnants. Evidence from clusters confirms our theories of stellar evolution. Compact objects: neutron stars, pulsars, quark stars, and black holes.

High-Mass stellar evolutionary tracks are quite different from the low-mass stellar evolution tracks. Notice that the core can heat up so fast that the envelope of the star tends to lag behind. Carbon fusion can start before the red giant phase.

Heavy Element Fusion - shells like an onion

Supernova 1987A seen near nebula 30 Doradus

1994

SN2005cs in M51(Whirlpool galaxy) discovered June 27, 2005

Supernovae in our galaxy have been infrequent. Historical supernovae in the Milky Way (none observed by telescope !!!!): Recent supernovae by date: All supernovae since 1885: Links for supernovae on the web: Latest supernovae (by current brightness !): Supernova SN2005cs in M51 (Whirlpool galaxy): also see:

Supernova Light Curves fall into two types

Two Types of Supernova (see following slides)

Type I Supernova is a “carbon detonation” and involves a white dwarf which completely explodes. As material accretes on the white dwarf from a binary companion, it’s mass finally reaches a critical limit, and the entire carbon core fuses to heavier elements, all at once.

A more elaborate theory of a Type Ia supernova might show how some planetary nebula get spiral shapes.

Type II Supernova is a “core collapse” and occurs when the core is finally pure iron, which cannot be fused to other elements. The core collapses to a big ball of neutrons, which causes a shock wave to bounce back outward, which blows off the entire envelope of the red giant, to form a supernova remnant.

Prior to detonation, the massive star can lose a large fraction of its mass. This material forms an expanding shell.

Computer simulations show lots of turbulence in the explosion.

Supernova Remnants Vela supernova remnant Other examples: Cassiopeia A (link) (link)link N63A (link)link Crab nebula

M1 – the Crab Nebula is from a supernova seen in year A.D The remnant is 1800 pc away and the diameter is currently 2 pc.

This supports the elaborate model of Type Ia supernovae

Supernova 1987A was not typical (link)(link)

Supernova 1987A linklink link link See mpeg animations of this.

Eta Carinae will probably go supernova in the next 100,000 years or so. SEDS link SEDS link

Cluster Evolution on the H–R Diagram

Newborn Cluster after 10 million years

Newborn Cluster after 10 million years Notice that there are already some red giants from massive stars that have already run out of hydrogen fuel.

Young Cluster after 600 million years

Young Cluster after 600 million years Notice that the cutoff is at Type A stars and that there are already some white dwarfs.

Old Cluster after 12 billion years

Old Cluster after 12 billion years Many more stars give a better statistical sample, and we see the main features of stellar evolution.

The Cycle of Stellar Evolution