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Astronomy and Lab

by: Alphonso Anderson

Astronomy and Lab ASTR 1030

Alphonso Anderson

GPA 3.89

Timothy Farris

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Timothy Farris
Class Notes
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This 70 page Class Notes was uploaded by Alphonso Anderson on Wednesday October 28, 2015. The Class Notes belongs to ASTR 1030 at Volunteer State Community College taught by Timothy Farris in Fall. Since its upload, it has received 33 views. For similar materials see /class/230702/astr-1030-volunteer-state-community-college in Astronomy at Volunteer State Community College.


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Date Created: 10/28/15
Thinking ofthe expansion in reverse the universe gets more compact as you go back in time leads us to the Big Bang Model the entire universe bagan as an infinitely compressed infinitely hot quotobjectquot that quotexpodedquotexpandin amp cooling We can get an idea of When the big bang occured by looking at Hubble39s constant how long does it take to cover 1 Mpc moving at 71 kms 6quot I quotNd 4157 0 OSLlr b aJLquot L 4 57 l Um W f 5 l rc i c5 6 nnVF 39 714 y M To get the km amp Mpc straight amp put the time in billions of years we need to multiply 1Ho by 980 f 7 b3 5 nabPk TI blin 744 lquot H t 7 K39 quotlt amp z l an 74 14 So start with a hot dense universe let it begin expanding and see what happens quotHistorv of the Universequot based on the big band model A The big bang occurs latest amp best data indicates 136 billion years ago B Inflation The MBR is very isotropic For many different places to be at the same temperature it implies they were all in close proximity to one another This is refered to as the quothorizon problemquot u We think that at some point during the first 10 seconds after the bang the universe underwent a brief period of extreme expanioninflation During this period the distance between points increased by a factor of 100times This solves the horizon problem because points that are now very far apart were in fact close together at the start and could be at the same temperature Inflation could be associated with a quotphase changequot at the subatomic level that would produce a dramatic change in volume in much the same way that water going from liquid to gas changes volume We haven39t as yet discovered a specific process that s consistent with the data but it39s a work in progress C Pair Production Two highenergy photons can collide and converttheir energy to mass E gt mcz producing matter and antimatter e fr 1 quot 7 20 t J 39L l 15 5 lo 5 A Jr a do I xhik e JLquot 6 E 4 Subtle processes produce slightly more matterthan antimatter As the universe cools antimatter annihilates witl matter leaving a little matter leftover After the first few seconds we have a universe with mostly energy photons but with its full complement of protons amp electrons D Primordial Nucleosynthesis A hot dense universe full of protons implies fusion of protons hydrogen into He Initially it was so hot that the He broke apart but for a brief period it became cool enough to preserve the He being fused yet still hot enough to keep fusion going lvf 14A T r 4 luv He m M4 uw I I 39 I MM 5 1 w Detailed calculations predict that fusion stops at a temperature of 1 billion K about 300 seconds after the big bang with 14 of the H protons fused into He This observation III E Decoupling Production of the MBR Universe was too hot for electrons to stick to H or He nuclei and make neutral atoms until about 400000 years after the bang temp 3000 K When atoms form most photons can then move freely for the rst timetheydecouple from matter We see these photons today in highly redshifted form as the MBRobservation IV The uniformity of the MBR indicates that the universe was very homogeneous at this time the slight variations in the temperature of the MBR indicate that there were very slight variations in density at this time Principle of Mediocrity the assumption that the laws of nature we see at work here on Earth apply throughout the universe quotOrganizing the view M We group stars in the same direction in the sky into constellations Technically a constellation is an officially recognized grouping of stars andthe region of sky around it There are 88 constellations An asterism is a group of stars resembling some object or figure like Orion39s Belt the Big Dipper etc Figure 143 Dismvering the Universe Eighth Edition N 2008 W H Freeman and Company Lcia39b GEMINI39 quotNebula g TAURU39SV39 Aldebaran ii In 739quot FBe39teilgeusi 39 39 Nebul39a Lquot I H V r Y I 39MONOCEROS quot a r v CAMS 39 39 x a 39 Ri gel o EAIDANUS 39 V Figure14b Discaveringthe iverseEighthEd1 o 2008 w HFr man and Company 4 it I if n 1 L6 quot39 5 Celestial Sphere We can imagine the stars planets etc are quotstuckquot on the inside of a very large ball with the Earth at the center This is the celestial sphere North celestial pole 90 declination Sun39s annual path around celestial sphere Celestial sphere iEarth sequator Jr g v I N Celestial equator Vernal equinox 0 hrs24 hrs celestial ole rlght ascenSIon p 90 declination Figure 13 Discovering the Universe Eignur Edition 2008 w H Freeman and Company The north amp south celestial poles are the points on the sky directly above Earth39s north amp soute poles respectively The sky appears to quotspinquot around the N amp S celestial poles The celestial eguator is the circle on the sky directly above Earth39s equator Celestial Coordinates We locate positions on the celestial sphere using the quotastronomical versionquot of latitude amp longitude declination dec like latitude the angle N or S from the celestial equator Measured in degrees right ascension RA like longitude the angle east from where the Sun is on the 1st day of spring Measured in quottimequot units hours minutes seconds of RA 24 hours 360 We measure angles or directions on the sky in degrees unless we39re talking about right ascension The quotangular sizequot of an object in the sky is the size of the angle from one side of the object to the other J r 5quot For small angles with divide a degree into arc minutes with 1 arc minute 139 160 an hjwlir J39ch I L flu t 30 We can divide arc minutes into arc seconds with 1 arc second 1quot 16039 13600 fhf r l lt4ju r Sf 73 x 15 La r5 2 9 quot I Definitions rotation the moving of an object about an axisinside the objectspinning Earth39s rotates once a day revolution the moving of an object about an axisoutside the objectorbiting Earth revolves around the Sun once a year Dailv Motion of the Skv The general daily motion of the entire skythe stars Sun Moon planets etc is to rise in the E amp set in the W traveling in arcs arcs across the sky The arcs are centered on a celestial pole Some stars that are close enough to the celestial pole will never drop below the horizon These are called circumbolar stars Sun39s Motion Daily same motion as everything else arcs across the sky form E to W Now if we look at a quotdayquot in detail then we find there are different quotdaysquot depending on our perspective solar day the time for Earth to rotate once relative to the Sun 24 hours sidereal day the time for Earth to rotate once relative to the stars about 23 h 56 m In addition to its daily motion the Sun has an annual or seasonal motion The Sun39s annual motion with resoect to the horizon rises S of E and sets S ofW in winter and is low in the S at midday Farthest south winter solstice rises N of E and sets N ofW in summer and is high in the S at midday Farthest northsummer solstice rises due E and sets due W on the 1st day of spring vernal or sorind eduinox and on the 1st day of fall autumnal or fall equinox And it will be midway up in the S at midday Quasars amp Active Galaxies Ch 17 Quasar quotquasistellar radio sourcequot The are point sources look like stars with highly redshifted spectra implying great distance They appear fairly bright from Earth but are very far away 2 10 billion light years away This means they are very luminous objects They are the most luminous continuous sources in the universe But they vary in brightness over time scales as short as just a few hours This implies the size of a quasar is less than a few quotlight hoursquot across lt 100 AU across We have seen that quasars lie at the cores of distant galaxies for many quasars we can detect a fairly typical galaxy surrounding the quasar Other Active Galaxies Active galaxies are galaxies that emit lots energy that is not from stars not black radiation Much of the energy comes from their cores or quotactive galactic nuclei or AGN39s Some particular types Sevfert Galaxies Spiral galaxies with brigh tarlike nuclei nd strong emission lines Figure 17 a Discovering rhe Universe Eighth Editinn o 2008 w H Freeman and Company Radio galaxies Ellipticals with strong emissions at radio wavelengths often with quotradio lobes which resemble jets quotshooting out from the core of the galaxy The lobes come from the AGN Figure 17 1 Iscavering the Universe Eighth Edition a 2008 W H Freeman and Company BL Lacertae Obiects Elliptical galaxies with bright highly variable cores Seyferts amp BL Lac39s are very similar to quasars and so it would be good to have a single model that would explain the behavior of all of these AG N39sactive galaxies What is the quotenginequot that drives the unusual energy output quotBestquot Model A supermassive black hole a the galaxy39s core is accreting material The material falling in toward the black hole froms an accretion disk orbiting the black hole As some material falls in very close it is ejected at high energy injets from either side of the disk The amount of material in the accretion disk determines the total energy output Quasar vs something milder like a Seyfert Accretion disk Supermassive black hole 15AU Fi 11111111 6a Our angle of view determines whether we see a SeyfertBL Lac quasar or radio galaxy 51 25 5 4 n Wquot 39 Figure 1 719 Disco vering the Universe Eighth Edition 2008 WH Freeman and Company Supermassive black hole with accretion disk and jets This observer sees a blazar or BL Lac object a This observer sees a quasar VThis observer sees a radio galaxy or doubleradio source Cosmology Ch 18 cosmology the study of the universe as a whole especially its origin amp development Assumptions 1 Principle of mediocrity 2 Homogeneous universe at large scales gt 100 Mpc the universe looks the same everywhere 3 Isotropic universe at large scales the universe looks the same in every direction s 2 amp 3 together make up theCosmological Principle the universe is homogeneous amp isotropic It implies there is no updown inout centeredge to the universe Observations that tell us about the universe as a Whole 1 The night sky is dark Hubble39s Law The more distant a galaxy the more its spectrum is redshifted Ll The visible matter in the universe is roughly 34 H amp 14 He with traces of other elements m Microwave Background Radiation MBR we observe blackbody radiation coming to us from all directions in space It corresponds to an quotobjectquot at a temperature of 27 K most intense energy comes in microwave wavelengths The radiation is almost perfectly isotropic variations are at the level of 1 part per 100000 or 00001 K Was discovered by Penzias amp Wilson of Bell Labs in 1964 Significance of these observations l Olbers39 Paradox If the universe is infinite in size amp eternal in time the sky should be bright The dark s y tells us the universe is finite in size or had a beginnin in time or both II The Expandind Universe The redshift of galaxies is interpreted as a recessional velocity It implies all galaxies are receding from each other with the more distant galaxies receding faster This implies the universe itself is expanding It s not that the galaxies are flying through space away from each other but that the space holding the galaxies is expanding Astrobiology Important quotthingsquot for life as we know it Liquid Water provides a medium for chemicals reactions quotuniversal solventquot provides a medium fortransport of nutrients provides a medium fortransport of waste Where to look for life where there39s water Carbonbased life Carbon of all the chemical elements has a balance of a being chemically active b forming a variety of stable compounds Other elements that are chemically similar to carbon like silicon amp germanium will form a variety of compounds but not to the extent of carbon amp not ones suitable for life quotThe Hortaquot episode of Star Trek 80 another requirement is carbon Note Life on Earth is everywhere It fills every nook amp cranny on the planet Does this mean that if a planet holds life will it fill the planet Hopefully not because that rules out everywhere else in the solar system Places in the solar system that may be candidates for life Mars possibility of underground water methane there could be microbial life under the surface Jupiter39s moons Europa Ganymede amp Callisto have saltwater oceans under their icy surfaces Saturn39s moons Titan amp Enceladus Enceladus has water geysers on it not sure if it39s ice or liquid water Titan has quothydrologicquot cycle of methane You could have life that uses methane as the liquid solvent instead of water What about life beyond the solar system First off suppose we wanted to travel to another star system To do so requires huge expenditures ofenergyamp ti e To go to a star that was 10 light years away suppose we could travel at half the speed of light150000000 ms The fastest humans have traveled so far is about 15000 mswe39re no where near having the technology to do that At half the speed of light it would take 20 Earth years to get there amp 20 years to get back Just consider a single astronaut not including the spacecraft supplies etc The energy required to get the astronaut up to speed stopped at the star back up to speed for the return trip and then stopped on Earth is equivalent to about 20 days worth of the United States39enz ire energy production It39s also equivalent to burning the Space Shuttle39s main engines for 33 years So basically travel between the stars is not feasible with our current technology and our current understanding of physics What we39re left with then is the possibility of communicating with another civilization The Drake Eguation Developed by Frank Drake a radio astronomer in the 196039 to help quantify the likelihood of communicating with any civilizations that might exist in our Galaxy N the of technologicallyadvanced civilizations in the Galaxy Iv R Crneg Kt I Lk onquot 54M Lth AIa fang 641 it 9 rw rm 7 ultrahan g gr a 5A1 51 nQJS f aquot thc A u 14 d Au Lcal h39ul sbfl lL A 139 F gl bLJv 5 Ihzls I39ll 1quot 1 I wLid 7 0445119 I veoft he L L JM z hf l LIL3r hkllijGh 4 hu bf 39 Ff od r39n 39 hitch w 3 C 1k 3 hu bv ffa 39l cLholoay ew aft L Aversjc 95 394 Loumum 4 49 611 l5 a 36 Let39s make an estimate of R4 79 We 7 lh yar charmss 33 03 In the systems discovered so far we have big planets close to the star But that39s skewed by our technique which is more likely to detect big planets close to stars I 1 6 spin 1 rr J4 JJ39 Equot lgl 57 Aquot haf 3 n no1 Y1 WS 5 01 L 39 lJ J slpu 1 u 09 g 02 392 L I Dlnsayaul 9 M 1 0 519 31 u x D 1gtClolaavyr NQV Consider the Sun39s motion with respect to the stars The Sun follows a path against the background stars the ecliptic taking 1 year to complete a cycle This motion is from W to E relative to the stars Why is it warm in summer amp cold in winter 581111 is closer in summerlfarther in 10 Winter r Longer days in summershorter in l f if j 0 winter r Sun is higher in summerlower in winter The angle of the Sun is the main factor When the Sun passes high overhead its energy is concentrated directly on the surface of the Earth When it is low in the sky its energy is spread over the Earth39s surface The more direct heating with the quothigh Sunquot produces the warmer temps The angle of the Sun the amount of daylight the ecliptic the Sun39s changing position over the course of a year etc are al caused by a 23 tilt in the Earth39s rotation axis relative to our orbit Vernal equinox Spring in the Northern Hemisphere I Winter solstice autumn In the Southern Hemlsphere Winter in the Northern Hemisphere summer in the Southern Hemisphere North Pole South Pole 1 l South Pole I South Pole Summer solstice Summer in the Northern Hemisphere Ecliptic sou h Amumna39 eqmn x Winter In the Southern Hemisphere Pole Autumn in the Northern Hemisphere spring in the Southern Hemisphere Figure 11 5 Discover39ng the Universe Eighth Edition o 2008 w H Freeman and Company Precession The ecliptic gradually shifts over time moving the positions 0 the equinoxes amp solstices relative to the stars It also gives us two different quotyearsquot 39 sidereal year the time for the Sun to complete one cycle around our sky relative to the stars or for Earth to orbit once relative to the the stars a l 3 5 L v 0 tropical year the time for the Sun to cycle from 1 equinox or solstice back to that same equinox or solstice Uc I llquot Lyquot 42 Mp ac ycer The cause of this difference is precession the Earth39s rotation axis quotwobblesquot like a spinning top with a period of 25771 years This changes the location ofthe ecliptic and ofthe N amp S celestial poles The Moon39s Motion Daily rise in the E amp set in W like everything else Longerterm Like the Sun the Moon moves W to E against the background stars moving about 12 per hour It takes abo one month to complete a cycle quotmoonthquot sidereal period the time for the Moon to make one cycle around the sky measured relative to the stars About 273 days synodic period the time for the Moon to make one cycle around the sky measured relative to the Sun It39s also the length of the cycle of phases of the Moon About 295 days The Moon39s Phases new moon When the Moon is in line with the Sun as seen from Earth not visible rise sunrise set sunset highest noon 1st quarter When the Moon has moved 90 E ofthe Sun We see a quothalfmoonquot shape rise noon highest sunset set midnight full moon When the Moon is opposite the Sun in our sky We see all the illuminated half of the Moon rise sunset highest midnight set sunrise 3rd quarter When the Moon is 34 ofthe way around its orbit We39ll see a quothalfmoonquot shape but the other half from 1st quarter rise midnight highest sunrise set noon Eclipses The Moon39s path is not exactly lined up with the ecliptic it39s tilted about 5 to the ecliptic lfwe happen to have new moon or full moon when the Moon is quotcrossingquot the ecliptic then the Sun Earth amp Moon aredirectly in line with each other Then we will have an eclipse Solar Eclipse When the Moon passes directly between the Sun amp Earth and its shadow falls on Earth Happens new moon L unar Eclipse Occurs when the Moon is directly opposite the Sun at full 77 mm I3 0 m Planetarv Motion quot A r quot 5 planets are visible to the naked Mercury Venus Mar Jupiter amp Saturn Over lon 39s of time they and Neptune amp Uranus mo ative to the background stars like the Sun amp Moo I unlike the Sun amp Moon the all move E to W against the stars for a period of time We call this quotbackwardsquot movementretroorade motion For Mars Jupiter amp Saturn retrograde motion happens around the time of opposition when the planet is opposite the Sun in our sky Mercury amp Venus are never very far fron the Sun in our sky retrograde motion for them occurs as they move from the evening sky E of the Sun to the morning sky W of the Sun Planets also appear brightest around the time of their retrograde motion quotSciencequot We want to develop a scientific explanation for these motions What is quotsciencequot It39s an approach to gaining understandin that39s based on the scienti c method Scientific Method r A D 5 r a lnl f kg r 94quot observe we see something happen in nature If we create a circumstance to observe experiment model develop an explanation of howwhy for the obsenation or experiment use geometry math quotcause amp effectquot Models must be testable they must make predictions that can be checked by obsenation or experiment This idea being testable also means that obsenationsexperiments can berepeated by other observers Models may be disproved by making wrong predictions and not standing up undertesting Models cannot be proved only verified the goal is not quotright vs wrongquot but quotaccurate vs inaccuratequot Pluto Charon amp Beyond Neptune Dwarf planet symbol E Pluto amp its moon Charon make up a quotdouble planetquot system Their Pluto orbital center is quotquotquot Hyda between two Charon Size amp Separation Pluto radius 1140 km 018 of Earth39s Charon radius 600 km 009 of Earth39s amp orbits 19640 km from Pluto 31 times Earth39s radius our Moon radius 27 of Earth39s amp orbits 60 Earth radii away Nix amp Hydra are no bigger than 200 km across and orbit abou 44000 km away Pluto amp Charon are unlike any of the 8 planets They are better classified as the firstdiscovered residents of what we call the Kuiper Belt The Kuiper Belt amp Oort Cloud The Kuiper Belt is a diskshaped region from Neptune out to about 500 AU from the Sun TheOort Cloud is a spherical region extending from about 500 AU to about 50000 AU from the Sun They contain objects that are mixtures of rocl and ice like Pluto amp Charon Pluto amp Charon are among the largest of these objects We39ve since discovered well over 1000 objects quotout therequot All with the possible exception of one are actually Kuiper Belt objects Current telescope technology makes it virtually impossible to see objects in the Oort Cloud llll Figure 91 Ba part 2 Dismvering the Universe Eighth simian 2008 w H Freeman and Company Some of the largest discovered so far Obiect Date size km Pluto 1930 1140 Charon1978 600 Quaoar2002 620 Sedna 2003 800 Haumea 2003 750 Makemake 2005 900 Eris 2003 1400 LaDysnomia quotaquot AU Deriaphelion 40 i 10 42 i 3 509 i 433 44 i 9 46 i 7 68 i 30 Other quotDebrisquot in the Solar System Comets Asteroids Meteoroids m Comets are small icy objects usually a few 1039s of km across They are usually in highly elliptical orbits 6 W 1 f 4 e law39s V 5 quotPartsquot of a comet The nucleus the comet itself a quotdirty snowballquot or an quoticy dirtballquot of dust rock amp frozen gaseswater C02 methane ammonia etcwhich vaporize when the comet nears the Sun As the ices vaporize they spew into space taking some rock amp dUSt Hydrogen creates the coma a Ve39m e cloud of gas and dust surrounding the nucleus than can be up to 1000000 km across Dust tail Discaverm the Universe Eighth Edition a 2008 w H Freeman and Company Matter amp radiation streaming from the Sun push some of the coma away forming the tais Two primary types ion tail Type I tail some of gas in the coma is ionized electrically charged by losing some electrons These atomsmolecules are driven directly from the Sun It will have a bluish color dust tail Type II tail The dust is driven away from the coma more slowly because each particle is more massive trailing out and behind the coma It will have a yellowish color Comet s orbit y Perihelion Dust tail Gas tail Figure 925 Discovering the Universe Eighth Edition o 2008 w H Freeman and Company Where do comets come from An individual comet cannot have lasted over the 4 12 billion years of the solar system Each time it passes the Sun it loses some of its material it will eventually run out of ices to vaporize There must be a source to supply comets on continual basis We need a quotresevoirquot of icy rocky objects far enough from the Sun that the ices won39t vaporize Comets come from the Kuiper Belt amp Oort Cloud One of these objects can get a gravitational quotkickquot from an outer planet from a passing star or from another Oort CloudKuiper Belt object and get shifted into an orbit that brings it in toward the Sun Asteroids Small rocky objects ranging from a few 100 km across to dust Most are on fairly circular orbits Most of the 100000 known asteroids orbit between Mars amp Jupiter in the quotAsteroid Belt Meteoroids Small objects that could collide with other objects When a meteoroid hits Earth39s atmosphere it gets hot enough to glowa meteor or shooting star Any piece of a meteoroid that is not vaporized and makes it to the ground is called a meteorite There are 3 basic types of meteorites found on Earth stones 95 quotironsquot 4 stonyirons 1 Stones are rocky irons are ironnickel stonyirons are a mix of rock iron amp nickel Stars m The apparent shift in an position when viewed from different loca ons In January In Julythe the nearby nearby star to star appears appears to be here be here Nearby star I The closer the sar the more its apparent position shifts as seen from Eartha Closer star A Earth 1 July I January I H Earth quot 7 7 Earth July 39 January Parallax of an even closer star Figu re 1 11 d Discovering the Universe Eighth Edition o 2008 WH Freeman and Company Parallax of a nearby star Figure 1 11 Dismvering the Universe Eighth Edition G 2008 W H Freeman and Company AAJie In r Pgre MauiTa anabquot of rL Fp l dx b i AF39 Parallaxes of stars are tinyeven the closest stars have parallaxes less than 1quot We measure parallaxes in arc seconds and use a distance unit based on that 1 parsec pc the distance at which a star would have a parallax of1 arcsecond 1 I 3 339 2 A 7 To calculate the distance to a star in parsecs you simply take the reciprocal of the parallax l i ha g r k x 39 Example The star 51 Pegasi has a parallax of 00651quot How far away is this star in pc amp in ly in parsec l Docr an 7 31 254100 f SAI39 7am A yQ M SLR 39I From the ground parallaxes can be measured out to about 30 pc 100 ly p 003quot which gets a few 1000 stars Using satellites we can measure out to a few 100 pc including about a million stars Proper motion the motion of a star across the sky due to its actual motion Brightness of stars 2 main factors that affect how bright a star looks from Earth 1 distance 2 luminosity the total energy emitted per second by the star We measure the brightness of stars using the magnitude scale with the larger the number the dimmerthe star We extend this scale to measure luminosities apparent magnitude the brightnessmagnitude of the star as seen from Earth absolute magnitude the brightnessmagnitude of the stars as would be seen from a distance of 10 pc away from the star measures the star39s luminosity S L A rw 40s 2434 atquot at y Moi quotquot 539 2cn ctr 61 w LL ILC Al I 34 132 F7 1 SlitBur f M a o Temperature amp Spectral Classes Stars were originally classified based on the strength of the hydrogen absorption lines in the spectrum A B C O P stronggtgtgt weak This was reordered into a temperature scale hot gtgtgtgt cool OBAFGKM 39 1311 m Foil F7 FgF L 49 w 2 Sizes of Stars For a given temperaturespectral class a larger surface area produces a greater luminosity This motivates luminosity classes which are really size categories supergiants la amp lb 10 1000 times the Sun39s radius giants ll amp Ill 10 100 times the Sun39s radius subgiants IV 1 10 times the Sun39s radius main sequence dwarfs V size of the Sun HertzsprungRussell HR Diagram It39s a graph of stars39 luminosity vs temperature which reveals many stellar properties LEA 1hquot7 F l IA ll F Aquot w kn an L uhAI M lt Surface temperature K 106 400 0000 8000 6000 500 3000 104 T102 5 1 r 1 Ill 0 5 E 3 l r l v r l rl N 0530 A0 F0 GO K0 M0 M8 yrl Spectral type 039 gure 1 17 is ave g the Universe Eighth Editinn a 2008 w H Freeman and Company We can read a star39s luminosity class off the HR diagram Smaller radius is to the lower left larger radius is to the uppe right lt Surface temperature K 10000 4000 2500 40000 20000 8000 6000 5000 3000 106 i r 39r i t lr 10 I 5 0 1 39U 102 o 3 9 gt E 395 1 5 3 1 c E a Q 3 lt 10392 7 10 10394 15 A0 FO GO K0 M0 Spectral type I O n Luminosity LO gt a r N r rquot 40000 20000 10000 5000 2500 lt Surface temperature K Figure118 Discovering the Universe Eighth Edition zoos WH Freeman and Company m for main sequence stars For stars on the main sequence the lower mass stars are to the lower right and highermass starsare to the upperleit 106 1 i Luminosity L0 gt it t i 40000 20000 10000 5000 2500 4 Surface temperature K Mass is the single most important property ota star determining its lifetime luminosity temperature etc Spectroscopic Parallax or quotspectroscopic distancequot A way to determine a star39s distance from its spectrum it we measure a star39s spectrum we can determine its spectral class and luminosity class Knowing these two properties of the star lets you plot it on the HR diagram and read off its luminosityabsolute magnitude Comparing this with the apparent magnitude yields the star39s distance This technique of measuring distances is called spectroscopic parallax it39s useful out to several 1000 pc The Interstellar Medium ISM The ISM is the matter between the stars It has two components gas amp dust g 34 H amp 14 He with 1 being other gases lt39s individual atoms or small molecules The gas makes up 99 of the ISM Densities average 1 atomcm3 about a million particles per cubic meter Lst smokesized particles about 100 nm in size made of silicon oxygen carbon iron assorted ice Only about 1 of the ISM Densities average 1 particle per million cubic meters The amount of material between the stars is about the same as the amount in the stars However the ISM is very quotclumpyquot We find the material clumped into clouds or nebulae singular nebula Molecular Cloud a dense region of the ISM as high as a trillion particles per cubic meter very cold 20K a few light years across but usually part of larger structures a few dozen pc across called molecular cloud complexes It is in these regions that stars form Chapter 12 Birth of Stars Agar is a ball of gas held together by its own gravity amp producing energy by nuclearfusion fusion the joining of 2 or more small nuclei into a larger nucleus and energy In most stars 4 H nuclei join to produce one He nucleus This requires very high pressures amp temperatures The basic picture of star formation is that a molecular cloud collapses under its own gravitational pull becoming compressed enough amp hot enough to start amp maintain fusion Let39s follow the birth amp life ofa star like the Sun 1 Collapse of the molecular cloud begins A molecular cloud begins to collapse typically due to a shocl wave from some external in uence explosions of nearby stars collision with another cloud Because the cloud is quotclumpyquot as gravity pulls it inward it will fragment into 1039s tc 100039s of smaller clumps each collapsing under it own gravity The fragments with enough mass will become individual stars Lasts 2 million years 2 Protostar The cloud fragment will become dense enough to trap photons so it begins to heat up more and glow from gravitational energy not fusion It has become aprotostar collapsing from about 100 AU lts surface is hot enough amp bright enough to plot on an HR diagram surface temp 3000K and rising core temp 1 million K lasts 1 million years 3 Convection begins with the protostar Convection begins to quotstirquot the protostar This allows the continued collapse increasing the core temperature while holding the surface temp fairly constant lts luminosity decreases surface temp 4000K core temp 5 million K and rising lasts 10 million years 4 Fusion begins When the core temperature reaches 10 million K fusion starts in the corequota star is bornquot The star39s surface gradually contract and heats up until the achieves a stable balance between the inward pull ofgravity and the outward pressure from the heatenergy being produced This balance is called hydrostatic equilibrium core temp 10 million K and rising surface temp 4500 K and rising lasts 30 million years 5 Main Sequence The star is now a main sequence star and will fuse H into He in its core in a stable manner for most ofthe rest of its life core temp 15 million K surface temp 6000 K last 10 billion years The particulars of how long the different stages last are specific to a Sunlike But all stars will go through these stages in their life The more massive the star is the faster it goes through these stages including the main sequence stage More massive stars have shorter main sequence lifetimes because even though they have more H quotfuelquot to fuse into He the greater pressure amp temp in their cores fuse the H at a greater rate Doppler Effect the apparent shift in the wavelength of a wave due to the motion of the source of the waveor the Observer Wave crest 1emitted when light source was at S1 Wave crest 2 emitted when light source was at S2 1 Wave crests 3 and 4 emitted when light source was at 3 and 54 respectively This observer sees redshift This observer sees blueshift Figure 415 Dis the Universe Eighth Edition 2 2008 w H Freeman and Company If the source amp observer areapproaching there is a shift to shorter wavelengths quotblueshiftquot If the source amp observer arereceding there is a shift to longer wavelengths quotredshiftquot The amount of shift in frequency is precisely dependent on the speed of approach or recession the quotline of sightquot velocity or quotradialquot velocity Astronomers want large telescopes for increased lightgathering ability increased angular resolution Our atmosphere distorts our views of objects in space The level of distortion is called the quotseeingquot and it gives an idea of the smallest details visible in any telescope Astronomers get around limits to seeing by put observatories on mountain tops observe from space or balloons compensate with quotactivequot control of telescope NonOptical Telescopes Radio Telescopes observe radio wavelengths from space These are the quotdishquot antennas Radio waves can reach us from inside clouds of gas amp dust in space where light can39t get out from allowing us to see starforming regions and other places we can39t see optically Interferometry by combining the signals of 2 or more radio dishes we can obtain the resolution of a telescope whose diameter equals the separation of the dishes l v 7 7quot l Can resolve to 000001quot best opticallycosistently 001quot Infrared IR telescopes detect the quotheatquot from objectsevents in space like dust in clouds young stars quotcoolquot objects etc Must be done from mountain tops balloons amp space Ultraviolet UV must be from space View hot stars exploded stars energetic events Xray amp Gammaray must be from space View very highenergy events very hot stars amp gas By observing the universe at all wavelengths we can learn much more about objects in space than we could just from one part of the spectrum C Figure 337 Discovering the Universe Eighth Edition o 2008 w H Freeman and Company Ch 4 Light amp Other EM Radiation Blackbody Radiation An object ata uniiorm temperature emits Ell waves overa range oiwauelengths in a particular way we calm The intensity of a particular wavelength depends on the temperature of the object With higher temperature Visible light Intensity gt 2000 Wavelength nm gt By looking at an object39s color we can tell its temperature Temperature scale We39ll use the quotkelvinquot temperature scale It39s basically the celsius scale set to start quotzeroquot at absolute zero instead of at the freezing point olwater water ireezes at 273 K boils at 373 K Spectroscopy Separating light or any EM waves into its component wavelengths for study is called spectroscopy 3 kinds of spectra are observed quotKirchhoff39s lawsquot If we take a solid liquid or a dense gas we39ll have a continuous spectrum a full range of wavelengths seen it39s the blackbody spectrum If we take a rarefied thin lowdensity gas and heat it until it emits its own EM energy we will see it emit just a few colorswavelengths emission lineswhich we call an emission line spectrum NOTE Each chemical element has is own unique emission spectrumlike a fingerprint If we let light shine through a thin gas we see gaps in the spectrumabsorption lines which we call an absorption line spectrum NOTE The absorbed colorswavelengths match the colors of that element39s emission line spectrum Formation of Spectral Lines Electrons e39s orbit the nucleus of the atom where the protons p and neutrons n reside in orbits with specific energy These orbits are distinct there are limited number of them in a particular element39s atoms and so the e39s only have a few specific energies available to them As e39s change orbits they release or absorb a single photon with a specific energy and hence specific wavelengthcolor 39 LI Aquot puny 7 J 7 l39 pqs fwu 1L c1 3 41 9 quot01 57 flair a f5 or e A1 of emission line spectrum absorption line spectrum Each element has its own unique orbits for the e39s since each element39s atoms have a specific of p39s in the nucleus Thus each element has a unique emissionabsorption spectrum What can we learn from an object39s spectrum 1 Chemical composition 2 Temperature 3 radial velocity Doppler shift 4 rotation rate Doppler shift broadens the Hnes 5 Pressure of gas broadens lines L 6 Presence of magnetic fields splits the lines due to the magnetic properties of e39s Formation of the Solar System The Earth amp planets formed with the Sun out of a collapsing cloud of gas and just a tiny bit of dust The gas is 34 H and 14 He accounting for 99 of the mass As the cloud collapsed the central region became very compressed an hot gt the Sun Increased density temperature rotation rate Vast rotating cloud of gas and dust Protosun forms begins to grow solar nebula begins to collapse Tens of millions f years 39 V quot Inner disk rock particles collide grow Outer disk icecoated dust particles collide form interiors attract gas that becomes outer layers Protoplanetary disk forms rock and ice particles collide start to form planetesimals Figure 53 part 1 Disco vering the Universe Eighth Edition o 2008 WH Freeman and Company Other material farther out quotfellquot or formed into a rotating disk Heat from the Sun drives the lighter gas out to the outer parts of the disk leaving the small fraction of dust in the inner regions Over a few 100 million years the dustice accumulates into small objectsquotplanetesimalsquota few kilometers across Inner disk rock particles collide grow Outer disk ice coated dust particles collide form interiors Protoplanetary disk forms rock and ice 39 attract 935 hat Several hundred becomes outer particles collide start to form planetesimals million years avers Accretion of terrestrial planets protosun becomes hot Terrestrial planet enough for nuclear fusion to begin in molten state Figure 5 part 2 Discovering the Universe Eighth Edition o 2008 w H Freeman and Company The planetesimals build into larger objects capable of growing larger by collision quotaccretionquot and by gravitational attraction The larger object grow larger by quotgobbling upquot smaller planetesimals At stage we call the bigger object quotprotoplanetsquot Accretion of terrestrial planets protosun becomes hot Terrestrial planet Several hundred enough for nuclear fusion to begin in molten state million years Jovian planet with core of rock ices Jovian planets accrete from gas in outer disk terrestrial planets heat up begin chemical differentiation Figure 5 3 part 3 Discovering the Universe Eighth Edition 2008 W H Freeman and Company In the outer part of the disk the planetismals and protoplanets also grow from collecting the gas and there39s a lot more gas forming large gaseous planets Jovian planets accrete from gas in outer disk terrestrial planets heat up begin chemical differentiation Jowan planet with Several hundred core of rock Ices million years Wind from Sun sweeps away gas and dust leaving planets moons asteroids Kuiper belt Oort cloud Figure 53 part 4 Disco verirrg the Universe Eighth Edition lt7 zoos w H Freeman and Company By about 46 billion years ago the solar system was in the form we see today We can divide the 8 planets into 2 groups The terrestrial planets Mercury Venus Earth Mars are close to the Sun small dense rocky rotate slowly have few moons no rings The iovian planets Jupiter Saturn Uranus Neptune are farfrom the Sun large lowdensity gassyliquid rotate rapidly have many moons amp rings Pluto doesn39t fit in either group After the Main Sequence Outer layers no thermonuclear reactions Hydrogen fusing shell Hydrogenfusing gt Heliumfusing core 439 core Mainsequence star Young redgiant star Redgiant star after helium fusion begins Eventually a star will run out of H in its core so it can39t carry out H gt He fusion Rule of thumb when the energy output changes in the core the core compresses and its temperature rises This causes the surface to expand and cool LGiant When the core runs out of H it collapses and heats up This increases the rate of H gt He fusion in a shell around the core Eventually the core temperature increases to 100 million K and He begins to fuse into carbon C and C He fuses into oxygen 0 This increase in tempenergy output it the core expands the star39s surface which cools off The star39s surface will be larger cooler and redder and more luminous surface temp decreases to 4000 K then increases to 5000 K size increases to 100 x Sun then decreases to 10 x Sun lasts 150 million years 7 Supergiant The star runs out of He in the core which again collapses and heats up This increases the fusion rate in the shells above the corean inner shell that still fusing He gt C and an outer shell fusing H gt He This swells the surface of the star into a supergiant surface temp 4000K size 500 x Sun lasts 10000 years 8 Planetary Nebula The supergiant is unstableits outer layers get pushed off into space as a planetary nebula This has a side effect of enriching the ISM with heavier elements especially the C lasts 100000 years 9 White Dwarf The star39s mass is too small to fuse C or O in the core into anything else Gravity compresses the core until it39s stopped by the electron degeneracy pressure A small hot core is left to gradually cool off over eons temp 100000 K and dropping size about the size of Earth The stages at least up through the supergiant phase are similar for stars a little less massive than the Sun and for sta heavier than the Sun Lowmass stars are fully convective a don39t build up a He core so they never go through a giant phase For medium to highmass stars the main difference the these phases is how long they take The more massive the star the quicker it goes through the stages 0 star 3 million years on main sequence G2 star 10 billion years on main seq M star 200 billion years on main seq Deaths of HighMass Stars Stars over 8x Sun39s mass can fuse carbon in their cores when they get to the supergiant phase They can even fuse elements up through iron in their cores but not heavier than iron TABLE 131 Evolutionary Stages of a 25MO Star Stage Central temperature K Central density kgm3 Duration of stage Hydrogen fusion 4 X 107 5 X 103 7 X 106 years Helium fusion 2 X 103 7 X 105 5 X 105 years Carbon fusion i M 6 X 10 2 X 10 3 600 years Neon fusion 0 12 X 109 4 X 109 1 year Oxygen fusion f z 15 X 109 1 X 10quotJ 6 months Silicon fusion I M 27 X 109 3 X 101 1 day Core collapse 54 X 109 3 X 1012 02 seconds Core bounce 23 X 10 4 X 1017 milliseconds Supernova explosion about 109 varies hours Table 131 Discovering the Universe Eighth Edition 2008 w H Freeman and Company With this different quotfusion pathquot the star has a very different end to its life With the production of iron in the core fusion shuts down suddenly and the core collapses almost instantaneously upon itself You39ve got the coreabout the size of a white dwarfEarthcollapsing to just a few km across The overlying shells of the star pile up on the core and rebound bounce back The star will be blown apart as a W The supernova can outshine an entire galaxy 100000000000 stars for a few weeks The energy of the explosion can fuse elements heavier than iron and it sends them off into space to be a part of the next generation of star formation SUpernova Remnant Cores If less than about 3 x the Sun39s mass is left in the core a ball of neutrons will be lef a neutron starwhich is about as heavy as a star but only a few km across As the inner gets smaller it quotcondensesquot the magnetic field of the star and its rotation rate greatly increases The neutron star will emit beams of radiation along its magnetic field and sweep those beams across space as it rotates If we happen to be in the path of a beam we39ll get pulses of energy like from a lighthousea pulsar lf over about 3 x the Sun39s mass is left then gravity collapses it completely into a black hole Relativity amp Black Holes Einstein39s Relativities 19051915 A relativityis a set of rules used to compare data gathered from different perspective M quot Galilean Relativim 5 15 39 l D Ar rpm Eh u D D fly 151 up 439 397 vf a 04quot 39 391 u 9 quot3a 5 rquot H 97 1 gt 5 I 07 CD sec 1341quot quotavquot3 35 as cam739 P phr439zi Einstein set out to resolve the cqu between this Galilean relativity and the law of39electror agnetism Lgll W 0 309 gt quot50 Einstein39s 2 postulates starting points to reconcile EM amp laws of motion 1 The laws of nature are the same for all observers regardless of their motion 2 The speed of light is the same for all observers regardless of their motion He first worked this out torspecial relativitydifferent observers are not accelerating relative to each other but can be moving Let39s look at some of theconsequences of these assumptionspostulates in special relativity The speed of light is an upper limit on all speeds Space and time are connected quotSpacetimequot Length contraction the length of an objectdecreases as it moves faster quotTime dilationquot time passes more slowly the faster you go quotTwin paradoxquot mass increases the faster you move E mc2 gt energy mass x speed of light2 There is an equivalence between mass and energy Either can be converted into the other Fusion in a star H gt He The He produced has slightly less mass than the H you start with The mass that39s quotlostquot is actually converted to energy and it39s the source of the energy of fusion Einstein next worked the consequences of his 2 postulates for general relativitv observers can be accelerating relative to each other It turned out to be a model of gravity Consequences all the consequences of special relativity apply Gravity can quotpullquot light It doesn39tsow the light but it stretches the wavelengthwe call it agravitational redshift Gravity or mass bends spacetime spacetime is dynamicit39s part of the process of nature time slows around mass 223 ar 175 arcsec Measured effect ofstar VEM bendIng Of 39 starlight by the 2 Because of the deflectionthe star 1 Sun appears to be here Sun I W Earth 3 1 A ray of starlight is deflected by the Sun s gravity ls relativity a theory of quotrelativismquot Black Holes 0 Escape velocity the speed needed to escape from an object39s gravity from Earth39s surface 11 kms As an object becomes more compact the escape velocity increases Take the Sun at its surface 620 kms shrink the Sun to the size of Earth white dwarf 6500 kms shrink it to the size of Tennessee 600 km across 30000 kms shrink it to the size of Gallatin 6 km across 300000 kms or 300000000 ms c When the escape exceeds c nothing can escape and we have a black hole The radius from the center at which the escape velocity equals c is called the event horizon or the Schwarzschild radius Any object or event happening within the event horizon is quotcutoffquot from the outside world b Boundary of 139 4pquot black hole bu 9quot Figure 145 Disco vering the Universe Eighth Editinn o 2008 w H Freeman and Company Material or objects far outside the blackhole would not notice any change in gravitational pull orbits etc for an object that collapses to become a black hole The mass of the object and the distance to it wouldn39t change Material nearthe black hole would eXperience severe tidal forces which become more and more extreme closer to the event horizon be pulverized by tidal forces orbita motions would be very fast friction andor rapid motions produce heat material to extreme temperature cause some of material to fall in toward bh light emitted would be redshifted by the bh39s gravity material falling in would take longer amp longer to fall in due to time dilation Accretion disk Black hole Figure 1419 Dismver39n the Univerie Eighth Edition to 2008 WHFreeman and Company We can39t see a black hole directly but we could look for the material around it hot gas orbiting a small object very rapidly V HDE 226868 a bluewhite supergiant Figure 1415 Mb Edmnn 2008 w HFreeman and Company Candidates for stellarmass black holes obiect mass x Sun39s siie how far away Cygnus X1 10 lt 300 km 7000 ly LMC X3 10 180000 y A062000 38 few km 2700 y


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