ASTR 1120ASTR 1120General Astronomy:General Astronomy:Stars & GalaxiesStars & Galaxies !omework #6on Mas"ring As#onom$due on Tuesday, %ov. 03, by 5p&If your CU clicker grade is 0 and you have been inclass, please send your clicker # to TA Thomas RogersThe Milky WayThe Milky WaySize of the Milky WaySize of the Milky Way••100-400100-400 billion stars• 100,000 light years indiameter• Sun (and us) arelocated ~28,000 light~28,000 lightyearsyears from the center,in the ‘Orion Arm’Artist’s sketchMilky Way Milky Way AnatomyAnatomy –– Spiral Galaxy Spiral GalaxyDisk, Bulge & HaloDisk, Bulge & Halo••DiskDisk:: includesincludesspiral armsspiral arms ----young, new staryoung, new starformationformation••Bulge & HaloBulge & Halo::older stars,older stars,globular clustersglobular clustersArtist’s sketchDisk is very thin!Disk is very thin!What Milky Way What Milky Way mightmight look like! look like!Spiral galaxyNGC 4414Galaxy NGC 4565 ! nearly edge-onWhat kind of object lie in the What kind of object lie in the halohalo of our of ourGalaxy?Galaxy?A. O and B stars.B. Gas and dust.C. Globular clustersD. Open clusters.E. All of the above.Clicker QuestionClicker QuestionWhat kind of object lie in the What kind of object lie in the halohalo of our of ourGalaxy?Galaxy?A. O and B stars.B. Gas and dust.C. Globular clustersD. Open clusters.E. All of the above.Clicker QuestionClicker QuestionWhere does most star formation occurWhere does most star formation occurin the Milky Way todayin the Milky Way today??A. In the haloB. In the bulgeC. In the spiral armsD. In the Galactic centerE. Uniformly throughout the MilkyWayClicker QuestionClicker QuestionWhere does most star formation occurWhere does most star formation occurin the Milky Way todayin the Milky Way today??A. In the haloB. In the bulgeC. In the spiral armsD. In the Galactic centerE. Uniformly throughout the MilkyWayClicker QuestionClicker QuestionAn important QuestionAn important QuestionHow do we know all we knowHow do we know all we knowabout the Milky Way?about the Milky Way?Mapping the Milky WayMapping the Milky Way••GalileoGalileo "For the Galaxy is nothing else than a congeries ofinnumerable stars distributed in clusters."••William & Caroline HerschelWilliam & Caroline Herschel (1785): star counts– Counted stars along 683 lines of sight using their 48-inchtelescope.Conclusion: Sun is in the centerand MW width is about 5 times its thickness6,500 ly30,000 lyShapleyShapley’’s s globular clustersglobular clusters• Harlow Shapely measured distances to globular clusters– These appeared to be centered on a location tens of thousands oflight-years from the Sun.Conclusion: Sun not in center, about 2/3 outHow Do Stars Orbit in Our Galaxy?How Do Stars Orbit in Our Galaxy?Stars in the diskStars in the disk all orbit in the same all orbit in the samedirection with a little up-and-down motiondirection with a little up-and-down motion• If they get too far above or below the disk, the gravityof everything in the disk pulls them back inOrbits of Orbits of stars in the bulge and halostars in the bulge and halo have haverandom orientationsrandom orientations• Evidence points to bulge and halo formed beforethe disk existed– Their orbits not affected (much) by the gravity of the diskWhy spiral arms?Why spiral arms?““Density wavesDensity waves”” ––stars move in andstars move in andout of denserout of denserregionsregionsLike Like ripples in a pondripples in a pondIn dense regions,In dense regions, starstarformation is moreformation is moreintenseintense, , so so ““armsarms””are brighterare brighterM51 - WhirlpoolM51 - WhirlpoolWhy do orbits ofWhy do orbits of disk stars bob up anddisk stars bob up anddown?down?A. They’re stuck to the interstellar mediumwhich moves like that because of its density.B. The gravity of disk stars pulls toward diskC. The halo stars push them back into diskD. Their orbits carry them out but then theybounce off the edge of the Galaxy and headback in.E. The density waves in the spiral arms kickthem out of the disk.Clicker QuestionClicker QuestionWhy do orbits ofWhy do orbits of disk stars bob up anddisk stars bob up anddown?down?A. They’re stuck to the interstellar mediumwhich moves like that because of its density.B. The gravity of disk stars pulls toward diskC. The halo stars push them back into diskD. Their orbits carry them out but then theybounce off the edge of the Galaxy and headback in.E. The density waves in the spiral arms kickthem out of the disk.Clicker QuestionClicker QuestionGalaxies: Ultimate Galaxies: Ultimate Recyling Recyling PlantsPlantsWhich generation of stars do youWhich generation of stars do youexpect to be more metal-rich?expect to be more metal-rich?A. Older population of stars (i.e. starsformed a very long time ago)B. Younger population of stars (i.e.formed more recently)C. No differenceClicker QuestionClicker QuestionWhich generation of stars do youWhich generation of stars do youexpect to be more metal-rich?expect to be more metal-rich?A. Older population of stars (i.e. starsformed a very long time ago)B. Younger population of stars (i.e.formed more recently)C. No differenceClicker QuestionClicker QuestionContents: Contents: Cold stuffCold stuff• Molecular CLOUDS– Mostly atomic hydrogen,some helium and othermolecules• Dark, dusty, cold– 10-30K• Emit molecularemission lines in far IR,radio••Orion imageOrion image here inhere incarbon monoxidecarbon monoxide (CO) (CO)––colors are Doppler shiftscolors are Doppler shiftsCOCODopplerDopplerImagesImagesMolecular clouds =Molecular clouds =star forming regionsstar forming regionsMapping Mapping ColdCold Hydrogen Hydrogen••Even the coldestEven the coldesthydrogen emitshydrogen emitsfaint emission linesfaint emission linesin thein the RADIORADIO••Change in Change in energyenergylevels of nuclearlevels of nuclearconfigurationconfiguration••Wavelength: Wavelength: 21 cm21 cmAll sky 21 cm radio mappingAll sky 21 cm radio mappingSemi-Warm stuffSemi-Warm stuff••Dust:Dust:––absorbsabsorbs visible visibleand UV lightand UV light––TransparentTransparent to tolonglongwavelengthswavelengths(red, IR, radio)(red, IR, radio)••Emits IR lightEmits IR lightHorsehead Horsehead NebulaNebulaDust+darkDust+darkmolecularmolecularcloudscloudsHorseheadHorseheadin close-upin close-upVLTVLT(Very Large(Very LargeTelescope)Telescope)••Hot starsHot stars