Chapter 5: Exoplanets
Chapter 5: Exoplanets 41087 - AST 115 - A
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This 4 page Class Notes was uploaded by Ashley Notetaker on Saturday September 26, 2015. The Class Notes belongs to 41087 - AST 115 - A at Missouri State University taught by Robert S Patterson in Fall 2015. Since its upload, it has received 100 views. For similar materials see Basic Astronomy in Physics 2 at Missouri State University.
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Date Created: 09/26/15
Note Highlighted information was also covered in lecture Stellar evolution and star formation are ongoing processes Detecting and studying new stars and planets require observation in various parts of the electromagnetic spectrum Most protostars are surrounded by protoplanetary disks Similar to what the solar nebula would have been like Asteroids and comets have also been observed orbiting stars Planets were first observed orbiting stars in 1992 Distorted protoplanetary disks If one or more planets orbits in a protoplanetay disk around a young star the gravitational pull will cause the disk to clump or warp or become off center from its star Some exoplanets have orbits whose plane is in our line of sight to the star Those exoplanets periodically pass or transit in front of the star This technique requires watching a fixed set of stars for years to search for those brightness variations All orbiting objects actually orbit around their center of mass a point located directly between them When one of the bodies is much more massive than the other the center of mass is very close to the center of the more massive body When a massive exoplanet is orbiting close to its star the center of mass isn t near the stars center If the planet moves toward and away from us then so does the star This is detected through the Doppler shift The length of one Doppler shift toward Earth away from Earth and back to starting point is the period of the planets orbit Many planets orbit their stars with some of their motion on the celestial sphere The stars orbiting with these planets move around their common centers of mass with a motion that appears to be wobbling back and forth on the celestial sphere Can t yet resolve most planets that have been detected Most planets are very dim compared to their stars Matter warps its surrounding space causing light to change direction The gravitational focusing of light from a distant star by the exoplanet gives a brighter image Pulsar Timing method Many neutron stars the remaining part of a star after a supernova have whirling magnetic fields that generate pulses of radio waves visible light and other radiation These stars emit the most regular pulses ever detected If the star has planets orbiting it the motion of the star around the center of mass can be detected by the change of timing in the pulses Some orbit sunlike stars Some orbit bodies that have too little mass to be classified as a star Some orbit burnt out star remains Some orbit groups of stars Most orbit stars in the Milky Way Few orbit global clusters large clumps of stars outside our galaxy Exoplanets are very diverse By observing transits astronomers can determine the spectrum of a planet s atmosphere and the chemical makeup of that atmosphere It can also determine the materials a planet is made of and its 3 O m 5 Stars w Multiple Planets Most stars w multiple planets are discovered using the transit method Astronomers watch the largest planet transit the star multiple times The interval between transits is the length of a year on that planet When there are other planets the gravitational pull on the observed planet will cause a change in the time it takes the observed planet to orbit the star Some planets orbit in the opposite direction that their star rotates this is the opposite of what the nice model predicts This has led to rethinking of the Solar Nebula Theory an ave I e I Ica or I s u o eccen no 0 a mos M yh h39ghly ll39pt39 l b39t pt t 39 39ty f l t 1 Many planets orbit very close to their star But some orbit very far away Star systems w high eccentricity are unlikely to have lifesustaining earthlike planets bc the changing location of massive planets is likely to prevent smaller planets from staying in order If nice model is correct then the planets formed further away and have been spiraling inward Some discovered planets don t orbit a star These are known as freefloatingrougeorphan planets Rogue planets give info about how often planets are expelled from orbit around stars Very few rogue planets have been discovered but calculations suggest there may be more rogue planets that stars in the Milky Way Habitable Planets Not all stars have habitable zones of 1AU Stars w different masses have different temperatures and emit different heat amp sunlight so they have a different habitable zone distance Life on Earth transformed the atmosphere and surface Plants Oxygen BuildingsForrests different surface No life has been found on exoplanets yet If there is life on Earthlike planets in habitable zone one would expect similar changes to atmosphere and surface Astronomers studying planets atmosphere by studying spectra of starlight to determine chemical makeup of the atmosphere
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