Stel Gal AstrCoReq ASTR 1211S
Stel Gal AstrCoReq ASTR 1211S ASTR 1020
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This 14 page Class Notes was uploaded by Dr. Deion Conroy on Monday October 12, 2015. The Class Notes belongs to ASTR 1020 at Georgia Southern University taught by Sarah Higdon in Fall. Since its upload, it has received 15 views. For similar materials see /class/222012/astr-1020-georgia-southern-university in Astronomy at Georgia Southern University.
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Date Created: 10/12/15
Previously Star Formation amp Molecular ISM Stars are born in cold clouds of molecular gas amp dust nomm Lec 9 Prof Sarah Higdon p 2 sm Formation and the ISM 3 mm WWW Muppymwmummp ymggmuumm radium mm l mmlgznnmuumman mm mmmnm mummy WWW mam umth mmmuwum zsmtarmallnmssllll um Pine wmm mu snowman Aunmvpmm whims ngus39 mm quotmm mm mum zmmuy amm new mm mum n Elm Star Formation Star formation happens when part of a dust cloud begins to contract under its own gravitational force as it collapses the center becomes hotter and hotter until nuclear fusion begins in the core L299 Pravsathlgdanp a When is The Gravitational Force Strong Enough When looking at just a few atoms the gravitational force is nowhere near stron nough to overcome the random thermal motion War inmmnan maltHall on Need 1057 atoms L299 PralSathlgdanpS Cloud Collapse and Fragmentation interstellar cloud l0 oarsecsl l000 solar masses amp l0 llt Starts to contract probably trlggered by shock or pressure Wae rrorn nearby star As it contra 5 the cloud fragments lrlto m or pleces Note dust mass l5 negllglble compared to gas mass BUT cri cal role as coolantshield and catalyst mommy Malammm quota lnlu39al cn apse m pmmam may take nnly z fzwrmillinn years L299 PralSathlgdaan Collapsing Clouds Dust Coolant Once a molecular it the atoms amp molecules collide this would increase the random and oppose maybe halt the collapse amp molecules convert en into infrared photons which does not heat up Random motions The cloud continues to Le 9 Prof Sarah Higdun p 7 Collapsing Fragments Individual cloud fragments begin t collapse 0 ce the density is high enough there is no further fragmentation 100 K not too different fromparent emperature is fairly uniform throughout fragment n N 106 particlesan sig higher density d N 10 2 km still 100x larger than the 0 ar System 106 x larger than the Sun Le 9 Prof Sarah Higdun p a Interior Heated by KelvinHelmholtz Contraction Tcm 10 K muchhotter n10 2 particlescm3 the density in the protostellar core is high enough that not all photons leak out easily Some stay and raise the temperature Collapse slows down in core Most of the protostar is still cold d 10 km about the size of the Solar ys em Stage am LE 9 mar Sarah ngdun p a Stage 4 Interior Much Hotter The protostar Stage 4 has the following properties Tam 106 K much hotterl n N 10 particlescm3 Density continues to increase rapidly in core which is no longer collapsing Colder gas at larger radius continues to rain d n it Can distinguish a photosphere and a dusty disk cocoon Stage an d N 102 km 100x the Sun s diameter LE 9 Prof Sarah nguun p in Proto Star Appears on the H R Diagram moon 7 Protostar hot core 10a K cooler surface 3000 K 46quot 100stun 9 7 mm Hg 6 h if gt UgAC uge su ace area 3 f highly luminous 103 Le thanks 3 39 Sun mm to StephanBoltzmann s Law E L mic 3 cm 1 R5 not yet hot enough to initiate fusion reactions in its core notyet a star A Le 9 Prof Sarah ngdun p11 A 1 5 Mo proxostar takes about 105 years to reach Arrival the main sequence Rates Like Main Sequence Stars more massive protostars evolve more quickly Luminos y Lo Note ass shown is Main Sequence while a 1 Mo protoskar takes much longeymore than 107 years 000 40000 10 0 00 5000 urface lempexalure K Le 9 Prof Sarah ngdu Stellar Nurseries Hidden Protostars a A dark nebula b A hidden protostar within the ula dark neb Le a Pruf Saran Higdun p is Evolutionary Track 1 Msolar MS Star Outer layers opaque H39 ions sur ce temperature of contracting star remains the same R decreases so decreases Later interior is ionized radiative transport more increases a bitas doesTsurf Eventually core contracts suf ciently to raise Tcore for fusion and hydrostat39c umnn 1nnnn mun 5m equilibrium is reach ed survmumim Le a Pruf Saran Higdun p 14 Evolutionary Track gt4 Msolar MS Star Horizontal Track Massive protostar contracts and heats more rapidly outer layers are not opaque so the temperature rises rapidly as the star contracts Hydrogen fusion able to start earlier gt mmmum luminosity stabilizes close to quotquotmw39m39m its MS value Star contracts ma om mun sun Su ata mamquot kl approx constant m lgdunpl Star Formation Note the main sequence is limited to the range 008 200 Msolar TOO small Brown Dwarf Too and the luminosity ramps up so fast that internal pressure rips the protostar apart During the process mass is both gained and lost Protostars eject gt 50 of their initial mass into the ISM Protostars accrete material from the circumstellar disk Left over debris forms solar system Le 9 Prof Sarah nguun p16 Star HH30 LEE 9 WWW rccr Pemsmv mm w in The Journey to The Main Sequence The protostar s luminosity decreases even as its temperature rises because it is becoming more compact Stage 5 Protostar shrinks to 10x the in luminosity The core s temperature continues to rise so Duo in mm uuun 5mm temperature K7 mwcam 5p clrai ciassmcawm 9 LEE 9 PM 53 H gm p WE CDWVDM L JZGGVFearmnFieniweHaii In Hydrogen Fusion And Joining The Main in non Lummastly lsalar ms Sequence c erature and gradually adjusts its radius It also b Hydrogen fusion initiated Still embedded in a diskc no can ofDust b orn Star I bn39ilm This is stage 7 p ar is now a new gum u 1 a The star continues to contract 7 t 7 t s mum Stu m s uuuw anon umquot it is in equ D the star has reached the Mal 9 B Q 5 M Sequence andwill remain there as long 1 r39lxmn ma as it has hydrogen to fuse in its core labillion years Lummastty solar unlvs an mm mm a sun anon Surtaee Vemuerature K B E 5 Le a Prat Sarah ngdun p 2n The most massive stars form from the most massive cloud fragments The least massive stars form from the least massive cloud fragments mat lt lwt lttw quottllllllm u t I wulllm w uh Nt nfiill There is essentially no evolution along the Ms Once a star gets there it stays put humuuwmwmm 0 am mm mm mummy WWW gunnu u m Mama mwmu ur hm nmavundamy m man munu munmum W n lnunn mamaquot mmuge mmwm Manquot 1 1 am mm mm mummy rummmmn er017mm mmammmm Pvmuullmuuulh g thka lnlhemnwnllng Kinsman Inn m human hlylrllEMrg mummkunammmnumnmm qu11m elumllanuhd mmhurx my my mam mwhxhl m min mmmmm LE a PM 5 W i l f mww Massive Stars can trigger new star formation in mm snau olhydlogun m nu mu ya been mum x mm m I Program Oldklflmm 0mmquot v xvm ngah 39 lumiuwulal Expandnavmlonol nnax4h gnmm umly hm ulggma m lamnon u um um w m um mum LE 9 Pruf Sarah mguun p 22 Supernovae Can Trigger Star Formation L229 PM 1quot Failed Stars Brown Dwarfs If mass of original nebular fragment too small N0 nuclear fusion Fusion gt008 Me or about 80K the mass ofJupiter fusion They just slowly cool off and dim ere may be as many Brown Dwarfs as there are stars in our Milky Way galaxy NV L uvy gm 23m Perm napits ml m Lat Hui Daren mguun a u Star Clusters Because a single interstellar cloud can produce many stars ofthe same age and composition star clusters are an excellent way to study the effect ofmass on stellar evolution Ammunmm e slarduskr N5 2254 b An w dugnm a m m in N5 1m L299 PravSavahngdan p 25 Open Cluster 50 million Years Old Yhi mam all Maughmalallu39 s a quothe an Equal Nylmgenlwon m begun in mimm a m w any of ma mu ya me name L299 pmsm Hem p 27 Globular Clusters Few mHhon stars noteme absence of masswe Mam Sequence star and me heava popu ated Red e am regwon T e turnoff pom 5 used to determmeme age of me duster Very O defound ne of me M ky Way outofme p a m W mm mm vu m cm wm smmemyawe xv L299 pmsm Hem p 25