Transcript Document
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. The Nature of Stars • Astronomy – Oldest science • Star – Fusion reactor in space – Ball of gas • All stars have a beginning and an ending Measuring the Stars with Telescopes and Satellites • Electromagnetic radiation • Measurement of photons – Wavelength – Intensity – Direction – Variation The Structure of the Sun • Structure – Stellar core (hottest part, dense gas in a plasmic state) – Convection zone (rising gas from the core that cools) – Photosphere (the region from which externally received light originates) – Chromosphere (red color, thin layer, hotter and more dense than the photosphere) – Corona (external plasma atmosphere that extends hundreds of thousands or millions of miles into space) • Solar wind – Stream of charged particles ejected from the upper atmosphere The Sun's Chromosphere and Corona Earth’s Magnetic Field Northern Lights The Sun’s Energy Source: Fusion • Sun’s energy source • Hydrogen (1 proton) converted to helium (2 protons) • Life expectancy is 11 billion years, and the sun is currently 4.5 billion years The Astronomical Distance Scale • Time – Light-years (about 8,000 miles per second, or 6 trillion miles in 1 year) – The closest star to our sun is Proxima Centauri at 4.3 light years away (25.8 trillion miles) • Measurement – Triangulation – Cepheid variable The Hertzsprung-Russel Diagram • Star groupings – Main-sequence stars – Red giants – White dwarfs The Birth of Stars • Nebular hypothesis – Pierre Laplace (gaseous clouds called nebulae rotate, cool, and gradually collapse and flatten due to gravity to form stars and planets) 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 Just how big are the stars? The Main Sequence and the Death of Stars – cont. • Very large stars – Successive collapses and burnings – Iron core – Catastrophic collapse • Supernova Star Explosion 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 Cosmology Chapter 15 Great Idea: The universe began billions of years ago in the big bang and it has been expanding ever since. Galaxies Edwin Hubble and the Discovery of Galaxies • Hubble – Largest telescope – Used Cepheid variable stars to measure distance to nebula • Galaxies – Hubble discovered universe is billions of galaxies • Cosmology Kinds of Galaxies • Spiral • Elliptical • Irregular and dwarf • Active galaxies – Quasars A Map of the Milky Way A Typical Spiral Galaxy A Typical Elliptical Galaxy How BIG is the Universe?? The Redshift and Hubble’s Law The Redshift and Hubble’s Law • Redshift • Hubble’s Law – The more distant a galaxy, the faster it recedes –V = H x d Photographs of Galaxies and Their Spectra What is the redshift?? Illustration of Hubble Expansion The Big Bang The Big Bang • Big Bang – The universe began at a specific time in the past, and it has been expanding ever since The Large-Scale Structure of the Universe • The Local Group – Milky Way, Andromeda Galaxy, and others • Groups, clusters, superclusters • Voids The Sequence of “Freezings” 10–43 Second: The Freezing of All Forces • Two fundamental forces – Gravity – Strong-electroweak force • Limit of our knowledge of universe Dark Energy What is Dark Energy?