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chapter 13 - Pa" 1 galaxies: normal and active EOCs ✴RQ 2, 5, 10 ✴P ✴DUE QUIZ DAY of Part 2!!! 2 ✴ the MWay is just one galaxy of hundreds of billions ✴ here we learn: 1. they ain’t loners, as in, they interact and collide!!! (gasp) 2. 90-99% of what’s out there is invisible - completely ✴ only extremely recently (last century) have we figured out what these critters really are ✴ we see in Ch 13 that there are different types and their interactions can transform them a b#ef h$tory ✴ French astronomer Charles Messier (1781) made huge catalogue of “nebulae...” ✴ called Messier objects Messier 42 (M42) Hercules Globular Cluster (M13) M16 M80 ✴ by 1908, astronomers found 15000 objects; what were they all? ✴ either nearby luminous clouds or faraway systems of pooploads of stars or both ✴ then Edwin Hubble (1923) found really faint Ceph Var in nearby nebulae, and the rest is history 13.1 % family of galaxies ✴ ironically the Hubble Space Telescope found there are literally billions of visible galaxies ✴ see enough, you see patterns ✴ and patterns can be organized… &e 'ape of galaxies ✴ we’ll see now: ✴ three basic types: spiral elliptical irregular ✴ and that the amt of gas and dust strongly influence what we get galaxy classification ✴ elliptical galaxies have no visible dust & gas ✴ and essentially no hot, bright stars ✴ classified from E0 (round) - E7 (highly elliptical) ✴ they can be monsters… …to dwarfs ✴ spiral galaxies have lots o’ dust & gas ✴ lots o’ O/B stars ✴ lots o’ star formation!!! ✴ and there are 3 types… ✴ Sa have large nuclei, less gas & dust, and not too many hot stars ✴ Sc have dinky nuclei, but lots o’ dust and gas, and lot o’ bright stars ✴ Sb’s are b/t Sa’s and Sc’s ✴ spirals also exist with bars = barred spiral galaxies ✴ classified SBa, SBb, and SBc • we’ve been barred! - SBb • some galaxies look like spirals without the spiral (!) • have a disk, a bulge, but no spirals and no O/B stars • called S0 ✴ irregular galaxies are a mess ✴ they have gas and dust and stars but no shape, disk, or bulge ✴ the LMC and SMC in the southern skies are irregular ✴ the LMC and SMC are gravitationally bound to us ✴ we are consuming the SMC now yum yum! ✴ and are active starformers, as seen here in the Tarantula Nebula in the LMC... ✴ last type NaCl galaxies ✴ small, not very luminous, ✴ usually only one spiral wrapped around on itself tastes kinda salty how many galaxies? ✴ using the Hubble Deep Field we can estimate >100 billion visible galaxies ✴ the selection effect wd tell us most are spirals ✴ but there are prob more ellipticals than spirals, and about 25% irregular quick quiz 1. Many galaxies were discovered in the 1700’s by a man whose name is still associated with many of them. Who was he? 2. Which type of galaxy can be spherical to flat? 3. Which type can be loosely wound to tightly wound? 4. Which type is filled with older stars and little gas? 5. Which type has stars moving in seemingly random directions? 6. Which two have active star formation? ✴ We can divide galaxies into three ✴ ✴ ✴ ✴ classes - elliptical, spiral, and irregular. There are subclasses which specify their shape. The elliptical galaxies contain little gas and dust and few young, bright stars. Spirals and irregular galaxies contain large amounts of gas and dust and are actively making new stars. Know Messier’s contribution. walk away wi& 13.2 measu#ng % prope"ies of galaxies ✴ what are their diameters, luminosities, masses??? ✴ know distance? then lum and diameter be EZ ✴ masses? they’re a bit of a pain… ✴ now we get into ✴ ✴ ✴ some steeeenking beeeg distances so we have to use megaparsecs (Mpc) = 3.26 million ly = ~20 million trillion miles to find the distances we need… )*ance Mpc ✴ distance indicators (aka standard candles) ✴ for close galaxies we can use Cepheid variables ✴ but they’re too dim beyond ~80 Mly, so… ✴ since we know the brightest globsters have M = –10, we can search for globsters in distant galaxies, then estimate distance ✴ astronomers have tried to use HII regions (the bright glowing red H regions) but that’s not too precise ✴ planetary nebulae, like paper lanterns, can be used ✴ supernovae (Type Ia) have a certain brightness and can be used at great distances ✴ but they are rare :( ✴ farther out we can use entire galaxies as dist indicators ✴ we know the average MWay-type galaxy has about 16 G L! ✴ the most distant galaxies we see are at ~10 bly (3000 Mpc) away ✴ which (remember) means we see them as they were 10 bya ✴ look-back time is unique to astronomy and will play a great role here ✴ but the biggest baddest most controversial distance “thing” is… &e hubble law ✴ Vesto Slipher (1910s) inspected spectra of many galaxies to look for life Vesto Schwarzschild ✴ he found most galaxies are red-shifted! ✴ they… are... moving… away!!! ✴ great astro history story, ✴ (Humason started as janitor at Mt W, went to Palomar to make great discoveries), but (sniff) anyway… in late 20s Hubble and Milton Humason published paper which said that the farther the glxy, the greater the red/shft! ✴ Humason at Mt Wilson in 1923 I used to clean this place. Humason, Hubble, older guy, older guy, Einstein, guy, zombie ✴ from the data we get a very simplified this: ✴ from this we get... wait! you tell me... ✴ the Hubble Law is based on that graph Vr = Hd " Vr = receding velocity (km/s) " H = constant (Hubble constant) " d = distance (Mpc) ✴ the Hubble constant can tell us the age of the universe! (more on that later) ✴ it’s being narrowed further and further, now thought to be ~70 km/s/Mpc ✴ that means that every Mpc something is away, it is traveling 70 km/s faster away from us ✴ simply now: if we can find how fast something is moving away from us, we can find its distance ✴ but we can’t know it too well; the exact Hubble const is still slightly elusive quick quiz 1. Name three light sources used as standard candles. 2. Who discovered that most all galaxies are moving away from us? 3. Who discovered that the farther away they are the faster they are moving away? 4. The Hubble Law can show us the distance if we know its ____? )ameter and luminosity ✴ if we know distance to a galaxy (not easy) we can use: geometry to find size (easy!) and apparent magnitude to find luminosity (easy!) ✴ what we find is… ✴ irregulars are relatively small and non-luminous ✴ we are larger than most spirals but there are some 4x bigger, 10x more luminous ✴ ellipticals have a huge range, from 1% our size ➙ 5x bigger than us ✴ your book has a nice perspective: ✴ if we were 18-wheeler size, dwarf galaxies wd be Hot Wheels, the biggest ellipticals wd be like a 747 ✴ what about mass?… mass ✴ this one’s tricky ✴ a rotation curve can be made using the Doppler effect for close-by galaxies ✴ the cluster method uses the movements within a cluster of galaxies to figure out how massive they have to be to do what they do ✴ smallest? 10-6 MMW biggest? 50 MMW dark ma+er in galaxies ✴ surprise! mass is not what’s expected ✴ the galaxies have too much matter, matter that can’t be seen!!! ✴ rotation curves show galaxies to have 10-100x more mass than we can see ✴ but wait, there’s more! ✴ some galaxies are ripping so fast around each other that there HAS to be unseen matter in the clusters to keep them from slingshooting away, and… ✴ X-ray pix show hot gas moving so fast it shd disperse, but it isn’t! • extra mass must be holding it there ✴ what is this dark matter? ✴ dunno! ✴ neutrinos might play some role (?) ✴ whatever it is, dark matter does play a MAJOR role in the future of our universe, whatever it is quick quiz 1. Which galaxy type varies the most in size? 2. Which can be enormously bigger than our galaxy? 3. Which make up the tiniest group overall? 4. What “stuff” is making the whole process of knowing galactic properties more difficult? walk away wi&...1 ✴ To know properties of galaxies we ✴ ✴ ✴ need to know how far away they are. We use Cepheid variables, globs, planetary nebulae, and supernovae as “standard candles.” The Hubble Law shows that the “radial” velocity of a galaxy is proportional to its distance. Vr = Hd ✴ The rotation curves of ✴ walk away wi&...2 galaxies show there is 10-100 times more dark matter than regular matter in a galaxy. Know Slipher’s, Humason’s, and Hubble’s contribution. 13.3 % evolution of galaxies ✴ now that we have the evidence, we need to build a case ✴ ✴ for how it all got here how did they form? why some elliptical, some spiral? clues lay in clusters… clu*ers of galaxies ✴ galaxies are not random!!!! they occur in clusters!!! ✴ there are ~3000 clusters w/i 4 Gly ✴ there are two types… • rich galaxy clusters have >1000 galaxies, mostly elliptical ✴ big elliptical guys near the middle (!) ✴ A trip to one of the galaxies there…. ✴ the Virgo Cluster is nearer and contains ~1500 galaxies ✴ has a great big bad boy in the middle, too (M87), but! ✴ not too crowded and contains lots of spirals • poor galaxy clusters aren’t too centralized, have <1000 galaxies, and have a subclumpy sort of look, like soup! ✴ we are in one (j/r) ✴ our local group is called… the Local Group ✴ only a few dozen here, scattered all over ✴ may be more but ✴ we can’t see them recently spotted the Sagittarius Dwarf, our old “nearest neighbor” (88 kly)... ✴ Sag dwarf is part of a stream we’re consuming a the moment... ✴ newest nearest neighbor (42 kly) also a stream we’re eating... ✴ and recently the Dutch discovered Dwingeloo, not part of the ✴ Local Group, behind the dense center of the MWay the RichGC and PoorGC give us clues into how they form… colli)ng galaxies ✴ there are lots of collisions going on and they help us ✴ ✴ ✴ figure out how galaxies evolve remember stars are stinking far apart, but galaxies are relatively VERY close to each other so they inevitably collide, although their stars almost never collide, their gas & dust do… ✴ when the gas and dust collide there is massive star formation ✴ and they don’t even have to collide, they can just harass, like The Mice ✴ harassment can trigger star formation and formation of spiral arms ✴ Stephan’s Quintet (300 Mly) ✴ Stephan’s Quintet from Gemini ✴ Stephan’s Quintet from HST ✴ we see in radio that there is a lot of invisible interaction going on, as well (with normal matter!) ✴ they may pass each other; they may collide ✴ if a small one collides with a big one, the larger consumes the smaller ✴= galactic cannibalism ✴ we will consume LMC, SMC, SAG dwarf, MMC, KFC ✴ here is the center of a ✴ monster galaxy; what do you see? sometimes we see multinuclei in the centers of big ellipticals implying cannibalism ✴ ring galaxies may have been formed by high-speed ✴ collisions and pass-throughs all these collisions and interactions help to determine what may have happened in the distant past… &e o#gin and evolution of galaxies ✴ first, what it can’t be (old ideas): ✴ellipticals cannot become spirals or irregulars (not enough gas and dust) ✴ellipticals cannot be young ✴spirals and irr don’t become ell’s by themselves ✴ bottom line: they do not change into another ✴ and it also appears that nobody grows up alone; collisions and mergers dominate ✴ ellipticals probably are the result of mergers, which triggered star formation which used up all the gas & dust ✴ starburst galaxies use up gas and dust quickly and their new SN blow away the rest ✴ an elliptical results Local violence (MW v Andromeda) Local violence (MW v Andromeda) Local View massive collision - cluster scale ✴ spirals have prob not had any collisions, they are ✴ ✴ fragile, and contain pooploads of gas & dust irregulars may be parts of galaxies ripped off during collision, or “we were never invited to galaxy formation in the first place!!!” sorta galaxies we’re just beginning to understand how galaxies are formed ✴ a great look-back ✴ ✴ time shows us lots of spirals, fewer and smaller ellipticals and they were much closer back then are we looking at the fragments that fell together to form today’s galaxies? quick quiz 1. What’s the difference between rich galaxy clusters and the poor ones? 2. What is the name of our local group of galaxies? 3. What major phenomenon is probably responsible for the shapes and sizes of galaxies? 4. What is galactic cannibalism? 5. What type of galaxy often results when one galaxy passes right through another? 6. What’s different about the galaxies we see far away and long ago? walk away wi&...1 ✴ Galaxies occur in clusters. ✴ We are a member of a tiny group ✴ ✴ called the Local Group. That is on the outskirts of a giant cluster called the Virgo Cluster. Rich clusters often have collisions, which force galaxies to go through massive star formation. walk away wi&...2 ✴ Collisions can strip away the ✴ ✴ gas and dust. Probably the different galaxy types form as a result of colliding, or not. Ellipticals are results of collisions; spirals have not collided. to be continued…