Lesson 5: The Formation of Stars and Planets
Lesson 5: The Formation of Stars and Planets ASTR 101
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This 6 page Class Notes was uploaded by Evan Kirkpatrick on Sunday October 18, 2015. The Class Notes belongs to ASTR 101 at University of Washington taught by Ana Larson in Fall 2015. Since its upload, it has received 18 views. For similar materials see ASTRONOMY (NW,QSR) in Environmental Science at University of Washington.
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Date Created: 10/18/15
Lesson 5 The Formation of Stars and Planets Vocab Star A dense cloud of gas that produces energy and light by fusing light atoms into heavier ones Kelvin Temperature Same scaling temperature as Celsius but it has a 0 point at 273C Planets Large round bodies that orbit a star Planetary System A system of planets and other small objects such as asteroids that orbit around a nearby star Solar System The planetary system that surrounds the Sun Interstellar Cloud A cloud of dust and gas in a space between stars Selfgravity Gravitational force among parts of the same object Hydrostatic Equilibrium When the forces acting on a cloud are evenly balanced o If an object has a stronger outward force than the selfgravity then the object will expand If an object has a weaker outward force than the selfgravity then the object will contract Molecular Clouds Densest coolest interstellar clouds composed of hydrogen Blackbody A source that absorbs and emits all the electromagnetic energy it receives Blackbody Spectrum A characteristic curve emitted by blackbody radiation Luminosity L Temperaturequot4 0 Also known as the StefanBoltzmann Law 0 Energy radiated per square meter is the ux 0 StefanBoltzmann Law constant relates ux to the temperature Flux 567x10A8 SB constant x Temperaturequot4 Wien s Law Peak wave length 29 x 10A6anT Nebula General term for interstellar cloud of gas and dust Meteorites Rocks that fall to Earth from space Accretion Disk A disk that forms from the accretion of material around a massive object Silicates Minerals containing silicon and oxygen Refractory Materials Substances capable of withstanding high temperatures without melting or being vaporized Volatile Materials Substances that become gases at moderate temperatures Comets lcy planetesimals that survived planetary accretion Dwarf Planets Planetesimals that didn t become planets but still orbit the Sun Kuiper Belt A body of dwarf planets on the outside of our Solar System Asteroids Small bodes found interior to Jupiter s orbit O Asteroid Belt A group of asteroids between Jupiter and Mars Comet Nuclei Small planetesimals that never were able to form and contain samples from when our planetary system had just formed Interstellar Clouds Stars and planets originally form from large clouds of dust and gas 0 These clouds are held together by pressure and selfgravity o All particles are gravitationally attracted to each other When there is a high enough density part of the cloud collapses to form either stars or planets Molecular Clouds Molecular Clouds Densest coolest interstellar clouds composed of hydrogen o If massive enough they can collapse under their own weight 0 Others collapse due to gravitational pull by near by stars 0 These collapse slowly Never uniform Denser areas collapse faster due to their selfgravity Because there are different areas of extreme density the cloud fragments into molecularcloud cores Force of gravity is inversely proportional to the radius Protostar Becomes a Star The innermost part of a collapsing molecularcloud core is called a protostar Gravitational energy is converted into thermal energy 0 As particles become more densely packed they move around faster and increase the thermal energy or heat 0 The more energy a star radiates the bluer it becomes The surface of a protostar is thousands of times bigger than the Sun 0 Therefore a protostar is thousands of times more luminous than the Sun Despite all the light emitted by protostars we cannot see most of it because 0 Protostar radiation is in the infrared spectrum 0 Protostars are buried in the heart of molecular clouds which are covered in dust that absorbs the remaining visible light Modern technology has allowed us to study the infrared light Dark clouds have been found to actually be dense cloud cores of young stars 0 Found in columns of gas and dust in the Eagle Nebula The Evolving Protostar At any given moment the protostar is in balance however the balance is constantly changing because of the changing weight and temperature around it o Gravitational energy is converted into thermal energy This heats the core and raises the pressure to oppose the increased gravity o This process continues to shrink the protostar and heat the core until it is hot enough to Ignite or begin fusing hydrogen into helium o The fusion releases energy that adds to the gas pressure to balance the protostar Protostar s mass determines if it can become a star 0 Must be about 008 times the mass of the Sun o If under 008 the star fails and is called a brown dwarf When the temperature reaches 10 million K fusion begins Planets Form Around the Protostar A piece of dust in a disk can have 3 actions 0 1 Become part of the star 0 2 Become part of a planet 0 3 Go back into interstellar space We nd planets orbiting stars in relatively at planes and in the same direction Angular momentum is a conserved quantity of a rotating system that depends on the distribution of mass and velocity Amount of angular momentum depends on 3 things 0 1 How fast the object rotates Faster More momentum o 2 Mass of the object More mass More momentum o 3 How the mass of an object is distributed relative to where the axis is Spread out mass More momentum A change in one of these quantities is always accompanied by a change of another 0 Eg As our Sun collapsed it spun faster and faster Conservation of Angular Momentum is the idea that angular momentum will remain the same if there are no external forces This idea presents an issue for normal clouds because angular momentum would imply that once the Sun is small enough it would completely rotate in 06 seconds Formation of the Accretion Disk All particles go clockwise or counterclockwise The upward and downward moving particles run into each other and cancel each other out leaving a at plane The angular momentum that we lost in the normal cloud is actually conserved in the accretion disk Creating Larger Objects Particles move around the disk and begin to stick together until they get to the size of large boulders For 2 large boulders to stick they must collide extremely slowly 01 ms If they collide faster than that then the boulders explode into small pieces Objects of about a kilometer in size are called planetesimals Inner and Outer Disks Have Different Compositions The inner disk is composed up of almost all refractory materials Farther out some volatiles like water are present in solid form High volatiles like methane and ammonia only exist in cold environments far from the Sun 0 Planets that form far from the sun contain refractory materials ice and organic compounds Chaotic encounters can change the orientation of planetary compositions Planet migration Sometimes planets end up far from where they are formed 0 Also can migrate when a planet loses some of its angular momentum to a disk material such a loss of angular momentum to disk material Slowly spirals to the central star Atmosphere in Solid Planets When solid planets are formed they begin to collect gas 0 Planets need to gather gas quickly before it gets dispersed by fast moving particles released by the Sun Larger planets capture gas faster Primary atmosphere is the gas formed during the planets creation Secondary atmosphere is formed later in the life of the planet The Solar System Terrestrial Planets Rocky planets like Mercury and Earth After formation of the four surviving terrestrial small debris continued to rain down on the surfaces 0 Seen as craters and dents Giant Planets Large planets formed of ice rock metal and other organic compounds 0 No solid surface but are much larger 0 Some people don t think these giants formed by accretion because it would take too long Composition of moons follow the same rules as planets in terms of composition of the moon 0 lnnermost moons have smallest amount of volatile material Planetary Systems Are Common Extrasolar Planet are planets that orbit Sun s other than our own 0 We know of over 1000 other extrasolar planets Search for Extrasolar Planets Many ways we can nd extrasolar planets Radial Velocity Method o Planets wobble as they move around their sun and we can infer the mass and distance from the sun based on the wobble 0 We can understand this because of the Doppler Effect Change in frequency due to motion 0 When an object moves towards us the light and sound waves ovenap o If an object is moving toward you the wavelength is shorter than the rest of it so the light seems bluer than it actually is This affect is called blueshifted o If an object is moving away from you the wavelength is longer than the rest of it so the light seems redder than it actually is This affect is called redshifted o The amount the wavelength is shifted by the Doppler effect is the Doppler shift 0 Doppler shift gives us the radial velocity or the part of motion that is toward or away from you 0 Spectroscopic Radial Velocity Method is the technique of nding extrasolar planets using the Doppler effect 0 This method requires bright light so it is limited to nearby stars Transit Method 0 We observe the effect of a planet passing in front of its star 0 The light from the star darkens slightly when the planet passes over 0 Measures the size of the planet 0 Earth must lie in the orbital plane of the planet for this to work Gravitational Lensing o A planet passes in front of a background star the star will brighten Effect is small so its sometimes called microlensing 0 Estimates mass of the planet Astrometry 0 Measuring the position of a star in the sky 0 Measures the amount the planet gravitationally pulls the sun Direct lmaging 0 Taking a picture of the planet 0 Hard to get because the Sun is extremely bright in comparison Other Planetary Systems Found many planetary systems similar to our own however most don t look like ours Hot Jupiters are gas giants that are much hotter because they are close to their stars 0 These don t follow our accepted rules of how planets are formed 0 Could have formed further out and moved in Some new planets are miniNeptunes and giantEarths All kinds of orbits and planets are being found These new solar systems are challenging how we think our planets formed
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