Unit 2 - Cosmology Part 1: Stars Part 2: Galaxies Part 3: Origin and Evolution of the Universe

Stars

What is a star? A star is a large, dense concentration of hydrogen gas that exists and collapses under the influence of gravity. A star changes as it ages because its composition changes. This happens as nuclear fusion reactions in its core convert elements to another element. Fusion in the core causes two hydrogen atoms to form a helium atom When a star runs out of fuel (hydrogen), it dies

A group of stars that form a pattern is called a constellation.

Constellations appear to move through the night as the Earth rotates. Many constellations change throughout the year as the Earth moves through its orbit around the sun.

Life Cycle Stars follow a definite development and destruction pattern that is referred to as the life cycle of a star

Nebula A star forms from a spinning cloud of gas and dust called a nebula Gravity causes the nebula to shrink The spinning nebula flattens into a disk of dust and gas

Protostar A protostar is the material in the center of a nebula that becomes a star As the protostar shrinks, temperature and pressure build up When the temperature and pressure are high enough, the protostar gives off light and heat It is now a star Watch: NZ0

(average stars) The most stable phase of stellar life Considered a middle age of the life span A star spends most of the time in this stage The Sun is a main sequence star

Life Span (depends on star’s mass) Massive Star (Large Stars) Swell into a supergiant Star will explode into a supernova Remaining matter collapses into an extremely dense ball called a neutron star Eventually becomes a black hole Average Star (Smaller Stars) Swell into red giant Explode into a nova Eventually will collapse into white dwarf or black star

The mass of a star controls its evolution, lifetime, and ultimate fate.

Dwarf Stars White Dwarf Blazing hot Small star Millions of years to cool Black Dwarf Dead Cold star Created when white dwarf cools so it no longer emits heat and light

Hertzprung-Russell Diagram NOT a graph NOT map of where stars are Plots stars based on their temperature, luminosity, magnitude, and mass

H-R Diagram Magnitude – Brightness Luminosity – Energy output of the star per second Temperature – how hot the star is (can also be called spectral class) Mass – how big the star is The most massive stars are the most luminous In the HR diagram, the temperature decreases as one moves to the right.

Watch:

Apparent magnitude describes how bright a star, planet or moon appears to be. 1 =brightest and 6= faintest. Absolute magnitude is how really bright a star is 32.6 light years away. Absolute magnitude is calculated by knowing the stars distance verses its apparent magnitude. Apparent vs. Absolute Magnitude

Galaxies

Light Year A light-year is the distance light travels in one year and is the most commonly used measurement for distance in astronomy.

Galaxies Galaxy- huge rotating “disc” of stars, dust, gas, and other debris held together by gravity Made up of billions of stars Estimated there are 100 billion galaxies in the universe

Galaxies are classified by their shape Three kinds: Spiral, Elliptical, Irregular

Spiral Galaxy – The Milky Way Made up of a central core usually contains a supermassive black hole Areas of stars resembling arms coming off of the central core Spiral galaxies have many young stars. The solar system is located in the Milky Way galaxy.

Elliptical Galaxy Have central core, but no arms. Stars are spread out evenly around the core. May be nearly circular or oval in shape. Mostly made of old stars.

Irregular Galaxies No central core No arms No organized shape They tend to be smaller than spirals and elliptical galaxies

The Universe

Space Radiation All of these things are in the deep reaches of outer space and are too far for us to see them directly. SO HOW DO WE KNOW THEY ARE THERE? All objects in outer space emit wavelengths of radiation that are part of the electromagnetic spectrum.

Electromagnetic Spectrum The electromagnetic spectrum can tell us what elements make up stars and nebulas. Spectroscopy is a technique in which the visible light that comes from objects (like stars and nebulae) is examined to determine the object's composition, temperature, motion, and density. Watch demo:

Electromagnetic Spectrum The electromagnetic spectrum can tell us can also tell us if stars and nebulas are moving towards or away from us. Doppler Effect – change in the wavelength as the emitting object moves closer or farther from the observer.

DOPPLER Blue Shifted – means the wavelengths are being compressed (the slinky is coming together) The object is getting closer to the observer, or wavelength receiver Red Shifted – means the wavelengths are getting elongated (stretching the slinky out) The object is getting further away from the observer or the wavelength receiver.

DOPPLER BEST PROOF FOR BIG BANG – expanding universe.

The Origin of the Solar System Solar Nebular Theory: Most widely accepted theory for the formation of our solar system. States that the planets were formed in a spinning, condensing cloud of hot gas and dust The dense concentrations of gas at the center of the disk eventually became the Sun. The planets were formed at around the same time as the sun

The Big Bang Theory The Big Bang theory is our best current model for the origin of the universe. States that the universe began in a very hot, dense state that expanded and eventually condensed into individual galaxies. This formation of galaxies continues to this day. Singularity explodes in the Big Bang 13.7 BYA

Future fate of the universe Big CrunchInfinite Expansion Big Rip

Future fate of the universe Big Crunch – Universe reverses expansion and shrinks back to a singularity in distant future

Future fate of the universe Infinite Expansion – Universe expands forever. Matter gets too far apart for new stars. Universe goes cold and dark.

Future fate of the universe Big Rip – Expansion of universe gets so fast that atoms cannot hold together. Universe rips apart and all matter becomes energy again, expanding into an infinite void