Chapter 9: Where Do Stars Come From? the Lives of Stars Some Stars Are Old, but Others Are Very Young; They Must Have Just Formed
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Chapter 9: Where do Stars Come From? The Lives of Stars Some stars are old, but others are very young; they must have just formed. What could these stars form out of? Empty Space? Space is Not _____ How do we know it’s there? 1. _______ 2. ________ ____ 3. _________ The Constellation Orion The Orion Nebula This material between the stars is called the ___________ _________ It is very diffuse and thin…. In fact it is almost a vacuum. The Interstellar Medium (ISM) The ISM is Visible as _____ Called Nebulae The Interstellar Medium is composed of: !Gas (99%) and Dust (1%) by mass • ________ (~75%) • _______ (~25%) • ____________ (< 1%) The Eagle Nebula Eagle Nebula Close Up (ground based photo) (Hubble Space Telescope) 1 Emission Nebulae (HII Regions) Three Kinds of Nebulae HII = Ionized Hydrogen Hot star shines on a gas cloud, 1) ______ Nebulae _________ the gas 2) ________ Nebulae Electrons jump to _____ energy levels 3) _____ Nebulae When they fall back to ground state they produce _______ lines. The Fox Fur Nebula The Cat’s Eye Nebula Reflection Nebulae Blue Reflection Nebulae and the Blue Sky When a cooler star illuminates a cloud of gas and dust, star light is ________ by the dust ______ wavelengths A reflection nebulae always appears _____ (blue light) are scattered more Reflection easily than Nebula near ____ The Pleiades wavelengths (red light) by small particles Close Up The Trifid Dark Nebulae Nebula • Reflection (blue) -> _____ star Dense clouds of gas and dust can _____ the light • Emission (red) - from the stars > ______ star behind them. Barnard 86 Horsehead Nebula 2 Where did the stars go? Interstellar Reddening • Interstellar Dust is in the way! • Solid particles ____ Dust blocks light coming from (shorter-!) ____ stars light better than (longer- !) ____ • Stars near edges light appear red because of _________ _________ Interstellar Reddening Observing _______ Stars Observations of Visible light from a ________ light newborn star is reveal stars on the trapped in the gas other side of the clouds cloud Observing Newborn Stars Observing the cloud in IR light can reveal the newborn star 3 Cloud Collapse How do stars form? How does a thin cold cloud of gas and dust become a • One of the 3 dense hot shining star? “origins” questions The problem is _______: • 2 Methods: ISM: 103 atoms/cm3 – Collapse caused by Star: 1023 atoms/cm3 ! _______ – Collapse caused by To become a star, the cloud _______ must _______ tremendously A star-forming nebula Gravity versus Pressure Star Formation • Gravity can create stars only if it can overcome the force of ______ ______ in a 1. Start with a cloud - ISM cloud 2. Form little _____ regions a. From collapse b. From shock waves 3. Dense regions collapse under ______ 4. Dense regions get ______ Fragmentation of a Cloud Fragmentation of a Cloud • This simulation • Gravity can overcome pressure in small begins with a pieces of the cloud turbulent cloud containing 50 solar masses of • Gravity becomes stronger as the gas gas becomes ______ • Gas becomes denser, core becomes ______ Fusion! 4 Fragmentation of a Cloud Fragmentation of a Cloud • The random • Each lump of the motions of cloud in which different sections gravity can of the cloud cause overcome it to become pressure can go ______ on to become a star • A large cloud can make a whole ______ of stars Star Formation from Shocks Isolated Star Formation • Gravity can When a high mass O type star overcome ends its life, it explodes as a pressure in a supernova relatively small cloud if the cloud is unusually dense Material from the exploding star might collide with a nebula in its path…. • Such a cloud may make only a single star Crab Nebula: A Supernova which exploded in 1054 AD Shocks Triggering Star Protostars Formation Henize 206 Henize 206 Part of a nebula (infrared) Shock waves can (infrared) condenses into a “push” material together in a cloud, knot of gas called creating _____ a protostar. ______ Protostars are surrounded by material which Proto-Planetary System can form ______. in The Orion Nebula. 5.