Our Cosmos.

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The Birth and Death of Stars

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Presentation transcript:

Our Cosmos

Pleiades cluster

Star field 1

… stars take on a range of colours ... Star field 2 … stars take on a range of colours ...

Classification of stars

Parallax method to determine distances to stars

Comparative sizes of stars

Hydrogen fusion

Pressure balance in a star thermal pressure = force of gravity

Explanation for physical properties of stars More massive star  higher thermal pressure  higher temperature  more luminous  faster fusion reactions  shorter lifetime

Hertzsprung-Russel diagram

Life history of the Sun

The Sun as a red giant

Red-giant Sun seen from Earth

Betelgeuse

Ring nebula

Cat’s eye nebula

Dumbbell nebula

Hourglass nebula

NGC 2440

Helix nebula … notice there is a small star at the centre of each planetary nebula …

White dwarf One basketball-full of white dwarf material weighs as much as an ocean liner

… an atom consists of mainly empty space ... Model of an atom … an atom consists of mainly empty space ...

Electron Degeneracy Pressure Pauli Exclusion Principle: No two electrons can occupy the same position in space Electrons are packed side by side in a white dwarf This prevents it from collapsing any further

White dwarf stars

Chandrasekhar limit The maximum mass of a white dwarf is 1.4 solar masses Above this, even electron degeneracy pressure cannot counterbalance gravity What is the fate of a star more massive than this? S. Chandrasekhar (1910-95)

Neutron star One pinhead of neutron star material weighs as much as two of the biggest supertankers

Final stages of red giant

Birth of a neutron star and supernova remnant

A supernova is one of the most powerful explosions in the universe Supernova 1987a A supernova is one of the most powerful explosions in the universe

Supernova in a distant galaxy

Crab nebula and pulsar

Pulsars Discovered by Bell and Hewish in 1967 Stands for pulsating stars, since they emit regular pulses Now known to be spinning neutron stars Joycelyn Bell and Tony Hewish’s telescope consisted of 2048 wire aerials suspended on posts in a field

Why a pulsar emits regular pulses

Pulsar animation

Vela nebula and pulsar

642 rotations/sec (fastest known pulsar) The sounds of pulsars PSR B0329+54 1.4 rotations/sec Vela pulsar 11 rotations/sec PSR B1937+21 642 rotations/sec (fastest known pulsar)

Cross-section of a neutron star