11Neutron star: your weight -http://www.youtube.com/watch?v=EXQKl-28zn021,000,000,000,000 lbsYou would be experiencing 140,000,000,000 g’s2Milky Way Galactic Inventory• Stars•Low-mass•Protostars•High Mass•Supernova•White dwarfs•Neutron stars•Black holes•Star clusters•Interstellar medium•Gas•Dust•Dark matter•Planetary systems•Planets•Debris•Light•Life•Astronomy classes•Love3Star-gas-star cycle4summarize how our view of the Galaxy has changedwith the measurements of the distances to globularclustersexplain how observations of stars and theinterstellar medium provide evidence for the structureof the disk of the GalaxyList 3 defining characteristics of each of the majorparts of the Galaxy: halo, disk, and bulge.Learning goals: be able to ….25How do we know what the Galaxy lookslike when we are trapped inside?Unraveling our place in the Milky Way6Winter Milky WaySummer Milky Way7We look at our innardsWe map out nearby roomsWe study characteristics of objectsWe look at nearby buildingsYou are here.8•We step outside (that is, we build bigtelescopes!)•What can we deduce from just what wesee here?39Two of the many ways of determining distances: Measured parallax - globular clusters are too far away VARIABLE STARS - RR Lyrae and lots of them10Variable stars as standard candles•Stars on or near thehorizontal branch•Fusing HeC in core•Have shell fusion occurring•Temperature range whereionization of H and He occursRR Lyrae variable stars11ADVANTAGES:•Periods of less than 24 hourseasy to identify•Found in uncrowded regions of a galaxy•Lots of themcome from old, low-mass starsDISADVANTAGE:•Not very luminous Mv=0.75RR Lyrae Stars12M3Canes Venaticihttps://www.cfa.harvard.edu/~jhartman/M3_movies.html4131785•1920’s: Harlow Shapleysystematically observed and mappedglobular clusters.•Center of globular clusterdistribution was NOT at Sun’slocation.•Center of MW is approx. 8 kpc or25 - 30,000 ly away.Shape and size of MW based onstar counts.You were here.Now you are here.14Summarize how our view of the Galaxy has changed with themeasurements of the distances to globular clustersAnswer this:15o Characteristics of the Halo Characteristics of the Disk Characteristics of the Nucleus and Bulge16NGC 4631 hot haloList 3 defining characteristics of each of the major parts of the Galaxy: halo, disk, and bulge.Milky Way hot halo517•Old, dim stars, some in globular clusters, some not.•Stars have only ~ 0.001 fraction of heavier elements as the Sun.•How do we know? Spectral analysis.Contents of the halo18Dark matter in the halohttp://www.newscientist.com/article/dn18344-milky-ways-dark-matter-turned-on-its-side.htmlHow do we know dark matter exists? It exerts a gravitational force.(You are a tiny speck here.)19Objects can be assigned to the halo or disk based on their orbits.Halo, Disk, and Orbits20 Characteristics of the Disk621 Atomic hydrogen21-cm line of “electron flip” Molecular hydrogen -- must trace CO emission Ionized hydrogen -- radio continuum Free electron and free proton interacting; proton accelerateselectron causing it to radiateExplain briefly about how observations of stars and the interstellar medium have providedevidence for the structure of the disk and bulge of the GalaxyDetecting hydrogen in the Milky Way: radio wavelengths22What kind of objectswould we want to pickif we wanted to observefar away?Visible WavelengthsVisible WavelengthsYou are here.Evidence for the structure of the disk of the Galaxy23H2Molecular hydrogenDetecting (CO)Evidence for structure of diskYou are here.24A. slightly higher thanB. slightly lower thanC. exactly the same asH electron spin interacting with its proton spinPhoton emitted from “flip” occurs because energy of oppositelyspinning proton and electron is ___when they spin in same direction.Must be collisionally re-excited.Rare, but so much H I in Universe,We observe lots of 21 cm radiation.725We assume that these objects are tracing spiralarms because we compared the patterns toA. this kind of galaxy:B. this kind of galaxy:C. this kind of galaxy:26Inferences from observed galaxiesMW @ IRwavelengths27Sun’s location inGalaxyList 3 defining characteristics of each of the major parts of the Galaxy: halo, disk, and bulge.Characteristics of the disk28 Characteristics of the Nucleus and Bulge829http://casa.colorado.edu/~ajsh/schwp.html22cMGrildschwarzsch=Schwarzschild RadiusThe radius of a black hole dependssolely on the mass of the black hole.For a solar-mass star, the radius isabout 3 km.For a 5-million solar masssupermassive black hole, the radius is15 million km.3031 What evidence supports the theory that there is a What evidence supports the theory that there is asupermassivesupermassive black hole at the center of our galaxy? black hole at the center of our galaxy? What is the supernova What is the supernova –– enrichment connection? enrichment connection?We cannot see the center of the MW.32Multiwavelength close-up of therecent massive star-forming regionnear the Galactic center.20-cm radio continuum (red)25-µm mid-infrared (green)6.4-keV line emission (blue).933Further evidence for energetic stuff happening at the centerof our galaxy34An envelope of 60-million-degree gasaround a youngcluster of 150 stars,known as the Archescluster within radiusof about 1 ly.•Chandra x-ray datadiffuse blue emissionin the inset box.•Hubble SpaceTelescope infraredimage (red)353.6 million solar massesList the evidence supporting the theory for a supermassive black hole at the center of our galaxy.361037yellow-white due to mix ofstarsstars reddish in color dueto old age, cool tempsoverall white color with bluespiral armsColornucleus; ring of gas and dustnear center; bar; SMBHSubstructure limited toglobular clustersspiral armsSubstructurelargely random orbits; somenet rotation about the centerstars have random orbitsin three dimensionscontents move in circularorbits in the Galactic planeDynamicsongoing star formation ininner regionsno star formation forpast 10 billion yearsongoing star formationNew Stars?gas and dust, especially ininner regionsLimited gas and dustfound in glob. clustersgas and dustISMyoung and old; more oldstars at greater distancesonly very old starsyoung and oldStar Typesfootball shaped, with a barroughly spherical;mildly flattenedhighly
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