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How Stars and Planets are Born Solar Nebula Theory Star and Planet Birth Nebula = Large gas and dust cloud (modern usage) From 1609 – early 1900’s almost every faint, fuzzy object was called a nebula. Star and Planet Birth Piece of the nebula contracts due to gravity and shock waves Often other stars forming at same time from other parts of the nebula Star and Planet Birth The region of the contracting nebula • Flattens • Rotates faster (due to conservation of angular momentum) Star and Planet Birth Center • Most of the matter • Protostar → Star • Protostar is a large object that’s not quite yet a star. • Forms from the contraction of part of a nebula Star and Planet Birth Disk • Smaller objects collide and stick to form larger objects • Warm near protostar • Lighter elements blown away • Cool further out • Lighter elements (H) stay • Water is frozen • Large, less dense planets form from H • See tutorial Star and Planet Birth https://public.nrao.edu/static/pr/planet-formation-alma.html Star and Planet Birth • Star formation happens within a cocoon of gas and dust • Often bi-polar jets Star and Planet Birth Protostar ignites = nuclear fusion A star is born Star and Planet Birth Strong stellar winds clear surrounding nebula • Heavy stuff cleared by collisions and close encounters • Light stuff cleared by strong stellar winds • https://www.noao.edu/image_gallery/html/im0557.html Evidence From inside our Solar System From outside our Solar System Evidence – From inside the Solar System • Sun at center - most of the mass • Sun and planets – not much else • Composition – mostly H & He like stars and gas clouds • Flat / planar (for the most part) • Preferred direction of rotation and revolution Evidence – From inside the Solar System Rotation and Revolution • How does rotation and revolution happen? • Everything is in motion • Random directions of motion get averaged out • Why so fast? • Angular Momentum demo Evidence – From inside the Solar System • Smaller objects form larger objects – meteoroids and comets • Craters Evidence – From inside the Solar System Distant leftovers • Asteroid Belt • Kuiper Belt • Oort Cloud (flung out?) Evidence – From inside the Solar System • Mini “systems” like Jupiter and Saturn Evidence – From inside the Solar System • Terrestrial vs. Jovian Planets • Outer solar system is cooler • Large, less dense planets form from H Evidence – From outside the Solar System Gas clouds in Milky Way • H & He Evidence – From outside the Solar System Stars form in groups from the same nebula Evidence – From outside the Solar System Strong stellar winds sculpt the nebulae Evidence – From outside the Solar System Stars form in cocoons with bipolar Jets Evidence – From outside the Solar System Disks of material around stars Extrasolar Planets (aka. Exoplanets) How to find Exoplanets • Doppler Shift (aka radial velocity) • Transit • Direct Imaging • Microlensing • https://exoplanets.nasa.gov/interactable/11/ How to find Exoplanets • Doppler Shift (radial velocity) • Orbiting planets cause stars to wobble in space, changing the color of light astronomers observe • https://exoplanets.nasa.gov/interactable/11/ How to find Exoplanets • Transit • As planets pass in front of their parent star, they block light from the star. Producing a dip in the star’s light curve. • https://exoplanets.nasa.gov/interactable/11/ How to find Exoplanets • Direct Imaging • Masking out the star itself to take a direct picture of material around the star • https://exoplanets.nasa. gov/interactable/11/ How to find Exoplanets • Microlensing • Light from a distant star is bent and focused by gravity as a planet passes between the star and Earth • https://exoplanets.nasa.gov/interactable/11/ Exoplanets How Many Have We Found (as of March 2017) • 3,461 Confirmed • 4,696 Candidates • 2,584 Star Systems • 325 Terrestrial http://exoplanetarchive.ipac.caltech.edu/