The Universe Chapter 14
The night sky Sky observations date to ancient civilizations Stonehenge was built in England for observing the sky.
The differences between stars and planets Stars Appear as point sources that produce their own light. They appear to move counter-clock relative to Polaris our north star Twinkle from atmospheric turbulence Distance measured in light years (ly): 9.5x1012 km/yr or 6x1012mi/yr. Planets Visible by reflected light
The celestial sphere Celestial objects are projected onto imaginary sphere around the Earth Celestial equator, is the Earth’s equator projected into the sky. Altitude angle and azimuth angle determine location on this celestial sphere. They act like latitude and longitude lines in space. Objects appear to rotate about north/south poles
Birth of a StarProtostar Phase to Main Sequence Star Gravitational collapse of a gigantic cloud of mainly hydrogen gas and dust produces a Protostar . When density, temperature and pressure increases until conditions are right for nuclear fusion a star is born. Temperatures of 10 million K must be reached for hydrogen atoms to be fused to other hydrogen atoms thus causing nuclear fusion.
Once fusion occurs and a star is born - • The gigantic cloud of gas and dust spends billions of years calmly shinning while it fuses hydrogen nuclei in the core. • When inward force of gravity equals outward pressure of fusion stars enter the main sequence where it will remain most of its life. • Life not observed but theoretically based on knowledge of nuclear reactions. • Predicted outcomes seem to agree with observations of stars today.
StarModel Core Very hot Nuclear fusion Radiation zone Diffuses outward over millions of years Convection zone Material rising from the interior, cooling, and sinking Visible “surface” of star Sun surface temp. ~5,800 K
Hertzsprung-Russell diagram • A graph used to plot where stars are in their life cycle. • Stars do not just stay in one star stage of the HR diagram • They enter different stages as their masses and temperatures change due to fusion.
Star types Hertzsprung-Russell diagram Plots absolute magnitude and temperature Each dot = star Stars grouping Main sequence stars Red giants Novas White dwarfs Cepheid variables
Lifetime of Our Star, the Sun Converts 1.4x1017 kg of matter to energy each year About two thousand seven hundred 6000 lb SUVs! Born 5 billion years ago, should last another 5 billion years. Lifetime depends on mass Our sun’s fate could be a white dwarf because of its size. Less massive stars have longer lifetimes More massive stars have shorter lifetimes
Brightness of stars Differences in stellar brightness is caused by- The amount of light produced by star The size of star The distance to the star
Absolute magnitude vs Apparent Magnitude Example- Our Sun Absolute magnitude = +4.8 Determined by a standard distance Apparent magnitude = -26.7 How objects looks compared to other objects around it. The more negative the number the brighter the object.
Star temperature(related to color of star) Colors appear as: red, yellow, bluish white Color related to surface temperature: Red: cooler stars Blue: hotter stars Yellow: in between (Sun) Classification scheme Based on temperature: hottest to coolest O, B, A, F, G, K, M
Blow-off- outer layers of stars form ring like structures called planetary nebulae
Death of Massive Stars Produces Supernovas Supernova Star collapses Elements beyond iron created in explosion and distributed throughout Universe More mass: more gravitational contraction and heat Critical temperature: 600 million K for supernova
Depending on mass that remains after the Supernova- Neutron star Remaining core between 1.4 and 3.0 solar masses Gravitational pressure fuses protons and electrons into neutrons Pulsar: rotating, magnetized neutron star Black hole Remaining core greater than 3 solar masses Gravitational collapse overwhelms all known forces Even light cannot escape the dense, compact object
Most stars exist in groups. Binary systems Two gravity bound stars Most stars are in binary pairs, not ours Star clusters Tens to hundreds of thousands or more gravity bound stars Often share a common origin Galaxies Basic unit of the Universe Billions and billions of gravitationally bound stars Larger scale still Clusters of galaxies Super clusters of galaxies Billions and billions of galaxies!
Early Astronomers • Galileo- used telescope to look at Milky Way and determined it was made up of a multitude of stars in about 1630.
The Milky Way Visible as a band in night sky. Billions of stars Spiral structure
Other galaxies Our nearest neighbors - the Local Group Dwarf galaxies ~1,000 light years across Nearest dwarf is disrupted gravitationally by the Milky Way Andromeda 2 million light years away Very similar to Milky Way Classification scheme (Hubble) Elliptical, spiral, barred and irregular
Possible suggestion of how God created the Universe is the Big Bang Theory
The life of a galaxy theorized by scientists Big Bang Theory Universe evolved from an explosive beginning about 13.7 billion years ago. Raisin bread theory Supporting evidence Microwave background radiation Large scale expansion Abundances of elements Diffuse cosmic background radiation The end: Expansion forever or the big crunch?