The Stars

Chapter 14

Great Idea:The Sun and other stars use nuclear fusion

reactions to convert mass into energy. Eventually, when a star’s nuclear fuel is

depleted, the star must burn out.

Chapter Outline

• The Nature of Stars• The Anatomy of Stars• The Variety of Stars• The Life Cycles of Stars

The Nature of Stars

The Nature of Stars

• Astronomy– Oldest science

• Star– Fusion reactor in space– Ball of gas

• All stars have a beginning and an ending

The Night Sky

Measuring the Stars with Telescopes and Satellites

• Electromagnetic radiation• Measurement of photons

– Wavelength– Intensity– Direction– Variation

Schematic Drawings of Telescopes

Keck Telescopes

Magellan Telescope

Orbiting Observatories

• Great Observatories Program– Hubble Space Telescope– Spitzer Infrared Space Telescope– Chandra X-Ray Observatory

The Hubble Space Telescope

The Anatomy of Stars

The Structure of the Sun

• Structure– Stellar core– Convection zone– Photosphere– Chromosphere– Corona

• Solar wind– Stream of particles

The Surface of the Sun

The Sun's Chromosphere and Corona

Earth’s Magnetic Field

Northern Lights

The Science of Life

• Why is the visible spectrum visible?

The Sun’s Energy Source: Fusion

• Sun’s energy source– Historical– Current

• Hydrogen

Fusion on the Sun – cont.

• Fusion– 3-steps-hydrogen burning

1) P + P D + e+ + neutrino + energy2) D + P 3He + photon + energy3) 3He + 3He 4He + 2protons + photon +

energy

• Life expectancy– 11 billion years

The Ongoing Process of Science

• The Solar neutrino problem

The IceCube Lab

The Variety of Stars

• Differences– Color– Brightness

• Distance • Absolute brightness

– Energy output– Luminosity

• Apparent brightness

• Behavior– Total mass– Age

The Astronomical Distance Scale

• Time– Light-years

• Measurement– Triangulation– Cepheid variable

The Triangulation of Stellar Distances

Cannon and Leavitt

The Hertzsprung-Russel Diagram

• Star groupings– Main-sequence stars– Red giants– White dwarfs

The Life Cycles of Stars

The Birth of Stars

• Nebular hypothesis– Pierre Laplace

The Eagle Nebula

Formation of a Planetary System

The Main Sequence and the Death of Stars

• Stars much less massive than the Sun– Brown dwarf– Glows 100 billion years

• No change in size, temperature, energy output

The Main Sequence and the Death of Stars – cont.

• Stars about the mass of the sun– Hydrogen burning at faster rate

• Move off main sequence

– Helium burning– Red giant– Begin collapse– White dwarf

The Life Cycle of the Sun

The Main Sequence and the Death of Stars – cont.

• Very large stars– Successive collapses and burnings– Iron core– Catastrophic collapse

• Supernova

The Interior of a Large Star

Star Explosion

Neutron Stars and Pulsars

• Neutron star– Dense and small– High rotation rate– Little light

• Pulsar– Special neutron star– Electromagnetic radiation– End state of supernova

Jocelyn Bell Burnell

Pulsars – Rapid Rotation and Intense Magnetic Field

Black Holes

• Black hole– Result of collapse large star– Nothing escapes from surface– Cannot see them

• See impact on other stars• Detect x-rays, gamma rays

Generation of the Chemical Elements

• Universe began with light elements• All objects made of atoms formed in

the giant stars