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Birth of Stars Astronomy The solar system Galaxies The Universe The Birth of a Star 1. Stars begin as diffuse clouds of dust in deep space 2. By chance areas with more dust form, and the increased gravitational attraction begins to pull more and more dust in 3. The cloud starts to collapse around the original concentration of matter, and pressure and temperature in the center increases. 4. Plasma forms as electrons are torn from protons 5. Nuclei come together and fuse – forming hydrogen 1. Energy increases pressure in the outer layer, balancing against the force of gravity – and the star gains stability Energy from the stars • 4 protons helium + energy (+ leftover particles) • The process provides the energy we see radiating from stars, and is self perpetuating A Star is Born • Energy from fusion pours out from the core, setting up a pressure in the surrounding gas that balances out the force of gravity • The star becomes stabilized 1. As the contraction starts, the rotation speed increases – like a skater who pulls her arms in while spinning 2. If nothing slow the rotation down, the speed will increase until the star is torn apart 3. One way that rotational energy is diminished is by the star splitting into a double star system 4. Another rout is for the star to spin off material in the act of forming planets Twin stars or Planets? • Most stars tend to take the twin star approach • This is one way that planets are thought to form – it is not the only way Stellar Lifetimes • The larger the sun, the greater the gravitational force, and the more energy is used in stabilizing the inward trend. • Every star must eventually burn all of its hydrogen • The larger the star, the shorter the lifetime The hydrogen in the outer layers is pulled inward by the gravity – it begins to fuse with the helium ultimately forming carbon. In the process the star expands greatly forming a red star White Dwarf: Diamonds in the sky • When the core has reached the point where they cannot be further compressed, and the star is stabilized by the upward pressure of electrons • This star is called a white dwarf. It no longer produces energy by fusion – but continues to glow as it cools off. • Stars up to 8 times the size of our star will become white dwarfs • If the star is very large, it burns through the hydrogen quickly; helium fuses to make carbon, and as the helium is exhausted the collapse of the core generates enough energy to fuse the carbon forming iron. • Eventually the star collapses, as the electrons are trapped inside the core, forming neutrons – thus a neutron star, or alternatively a black hole is formed. Neutron Stars & Black Holes Hertz sprung-Russell Diagram • The Main Sequence of a star's life is the period of time that begins after the star is "born" starts burning on its own, and the time that the star starts dying • The hotter a star burns, the more quickly it uses up the helium that fuels the nuclear furnace at its center. • Cooler red stars burn their fuel much more slowly. As a result, they can remain on the main sequence for many of billions of years before they begin to die. The Planets of the Solar System • Planets are categorized according to composition and size. There are two main categories of planets: – small rocky planets (Mercury, Venus, Earth, Mars, and Pluto) – gas giants (Jupiter, Saturn, Uranus, and Neptune) The Relative Size of the Planets in the Solar System My very educated mother just sat up near Pluto Rocky Planets Mercury, Venus, Earth, Mars, Pluto • They are made up mostly of rock and metal. • They are very heavy. • They move slowly in space. • They have no rings and few moons (if any). • They have a diameter of less than 13,000 km Characteristics of Gas Giants Jupiter Saturn Uranus Neptune • They are made up mostly of gases (primarily hydrogen & helium). • They are very light for their size. • They move quickly in space. • They have rings and many moons. • They have a diameter of less than 48,000 km Galaxies • Stars are gathered into clumps called galaxies • Our solar system is part of the Milky Way • Our galaxy is only one among billions links • Essential for teachers Earth and space science • (select Session 8. Order out of Chaos: Our Solar System )