Nebulae Massive clouds of dust and gas “Nursery” for stars: Stars born from the gas and matter Give off infrared, ultraviolet, X-ray, and radio radiation Chapter 20- The Universe

Characteristics of Stars Differ in many features: -size -mass -color -temperature -brightness

Size Sun’s diameter = 1,392,000km or about 109x diameter of Earth Sun is a medium-sized star Make up a majority of the stars in the sky From 1/10 th to ~10x the diameter of the sun

Giant Stars- 10x to 100x diameter of the Sun Aldebaran (45x) Supergiants- Up to 1000x diameter of the Sun Rigel, Betelgeuse, Antares

Red/White Dwarfs- Diameter less than a 1/10 th of the Sun Some are smaller than Earth Neutron Stars- Diameter may be as small as 16km

Composition of Stars Composition of stars is determined indirectly using spectroscope Element “fingerprints” show in light produced by star Most common element = hydrogen (60-80%) Helium is second (10-49%) Other elements (~4%)

Surface Temperature Color a hot object gives off is an indicator of its temperature Color of star is proportional to surface temperature Red o CRed-Orange o C Yellow o CWhite- 10,000 o C Blue/Blue-white- 35,000 o C

Brightness Depends on: -Size -Surface temperature -Distance from Earth

Apparent Magnitude- brightness of a star as it appears from Earth Absolute Magnitude- amount of light a star actually gives off (produces) Variable star- brightness of star varies over time Cepheid variable- changes size as well as brightness in cycle

Hertzsprung-Russell Diagram Shows relationship between absolute magnitude and the temperature of stars Discovered as the absolute magnitude increases, the temperature usually also increases

Surface temperature along X-axis Absolute magnitude along Y-axis Most stars fall into an area from upper-left to lower right: Stars in this area is known as main sequence stars Ex.- Sun, Sirius, Barnard’s Star

Stars no longer on the main sequence have changed as they have aged Area to upper-right of main sequence has giants and supergiants Area to lower left of main sequence has white dwarfs

Why Stars Shine Gravitational force within a star’s core is intense Brings together hydrogen in a very dense, very hot phase Hydrogen fuse together to form helium atoms and energy: Nuclear Fusion Fusion forces balance out gravity

In the Sun: 600 billion kg of hydrogen fuses into  billion kg of helium Every second!!! Missing mass changed into energy Energy takes forms across the electromagnetic spectrum

Review of the Sun Layers: Core- nuclear fusion takes place Radiative Zone- energy and particles from core move upwards Convective Zone- large convection cells carry energy upwards

Photosphere- visible “surface” of the sun Chromosphere- middle layer of sun’s atmosphere Corona- last layer of atmosphere; upwards of a million degrees Celsius

Evolution of Stars Life cycle of stars Protostars New stars born from gases and matter in nebulae Form from spinning disks of hydrogen gas and matter

Medium-sized Stars Main factor that shapes a star’s evolution is its mass When almost all hydrogen is fused into helium, core begins to shrink & heat up Causes outer envelope of hydrogen to expand greatly Envelope cools and color reddens

Now called a Red Giant Hydrogen continues to burn in envelope Helium begins to fuse into carbon at 200 million o C When all helium is fused, star sheds it’s hydrogen envelope to form planetary nebula White dwarf is left behind (core remnant)

White Dwarfs Gravity squeezes matter of star Very dense Continues to shine with white hot light Eventually cools to a cinder called a black dwarf How long depends on original mass of star: The higher the mass, the shorter the life-span

Massive Stars At formation, have at least 6x mass of Sun Evolution is much different than a medium- sized star Have similar life until they become red giants, or supergiants

Unlike medium-sized stars, gravity collapse will heat core after helium-carbon reaction When core reaches 600 million o C, carbon fuses into heavier elements (O, N, Ne) Cycle continues until iron and nickel are produced (Fe & Ni)

When iron barrier reached, core heats up tremendously and the star explodes Produces a supernova Core temperature can reach 1 billion o C Iron fuses into heavier elements All matter in the star is scattered in all directions New stars can form from matter and gas

Neutron Stars Small remnant is sometimes left after a supernova Extremely dense Spins rapidly: may give off radio waves that can be detected on Earth Neutron stars like this are called pulsars

Black Holes Stars with 10x or more mass than the sun Core remnant so massive, gravity collapses all mass into a single point Infinite density Extreme gravity: warps space and time around it Unknown what occurs inside

Galaxies Contain various star groups Major feature of the universe May be more than 100 billion galaxies in the universe!

Three main types: Spiral galaxies- Milky Way; Andromeda Shaped like pinwheels, with spiral arms

Elliptical galaxies- Form globular spheres to flattened disks Normally composed of older stars

Irregular galaxies- No definite shape Much less common than spiral or elliptical

Milky Way Galaxy Home Sweet Home Flattened disk with a central bulge Central bulge holds a massive black hole ~100,000 light years across Sun is located on edge of a spiral arm ~30,000 light years from center Stars rotate counter-clockwise around center

Formation of the Universe Stars on the Move Light travels to Earth as waves If object producing waves is in motion, then waves will either compress together or move apart Doppler Effect

Blue Shift- Light from a star is compressed and shifted towards blue end of spectrum Object moving towards Earth Red Shift- Light from a star is expanded and shifted towards red end of spectrum Object moving away from Earth

Astronomers discovered almost all galaxies were red-shifted Expanding universe: Galaxies at edge were moving away from center very fast Galaxies near center were moving slower, but still away What could account for this observation?

Big-Bang Theory Explains red-shift States that the universe began to expand with the explosion of an infinitesimally small, hot, and very dense point of matter and energy Occurred some 15 to 20 billion years ago

Observations: Red shift Background Radiation: Energy expanded along with matter If B-B Theory correct, background radiation from explosion should be the same no matter where you look It is…

Once the universe cooled enough that the energy could become matter, gravity took over Pulled together clumps of matter Formed larger and larger clumps Galaxies formed from this matter

What will happen to the universe? Two ideas: Open Universe Universe will continue expanding until all energy is used End will be cold, dark – Nothingness

Closed Universe Gravitational attraction between galaxies and matter will cause universe to slow down and eventually contract Original hot, dense, and SMALL point of energy/matter will form again Big Crunch