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Discovery of Other Galaxies: Ch 51, Archives Read Chapter 53, Secrets

Discovery of Other Galaxies: Ch 51, Archives Read Chapter 53, Secrets. Prologue: The Universe as we know it was revealed to astronomers on New Year’s Day 1925. The man responsible, Edwin Hubble, was not present. His historic paper was read to the 33rd annual meeting of the AAS.

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Discovery of Other Galaxies: Ch 51, Archives Read Chapter 53, Secrets

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  1. Discovery of Other Galaxies: Ch 51, ArchivesRead Chapter 53, Secrets Prologue: The Universe as we know it was revealed to astronomers on New Year’s Day 1925. The man responsible, Edwin Hubble, was not present. His historic paper was read to the 33rd annual meeting of the AAS. The Milky Way was suddenly humbled, becoming just one of a multitude of galaxies residing in the vast gulfs of space.

  2. Gathering Views of the Spiral Nebulae At the end of the 18th century, William Hershel had cataloged 100’s of spiral nebulae. He, I. Kant, T. Wright thought them “Island Universes”, distant Milky Ways. • William Huggins (19th century) took spectra of some and saw • that the disorganized ones were composed of just hydrogen gas. • Perhaps all were gas clouds in the MW? • Maybe “spirals” were solar systems just forming in the MW? • (called the “nebular hypothesis”). Or star clusters forming in MW. • From 1890-1920 a good deal of evidence was collected on both • sides. This became the most pressing question of its day!

  3. Question If you observed our solar system from afar, what would look different about our solar system than a spiral nebula? Can see satellites (i.e., planets) Can’t see spiral arms of light Can’t see central brightness answer, b)

  4. Andromeda, Biggest Spiral Nebula, Central Role What do you see? 1888 astro-photograph Proto- solar system, collision of a star with a gaseous nebula, or a twin to the Milky Way?

  5. The Great Debate Heber Curtis Harlow Shapley To resolve the scale of the Universe and the nature of the Spiral nebulae April 26, 1920 at the Smithsonian Museum of Natural History, arguments written in 1921 Shapley: Milky Way was immense (Sun off-center) and contained the spiral Nebulae, which themselves were close (inside MW) and small. Curtis: The spiral nebulae were “island Universes” (hypothesis) same as MW but far away (Sun at center of MW).

  6. If size of MW If Andromeda like MW, how far? 200’=1.2x104”=0.06 radians =50 kpc/D so D=800 kpc (and Opik 1922 got this same from brightness=MW) r=50 Kpc D • =200’ The Debate Points Some were wrong, some were right and correctly understood, and some were right but wrongly interpreted due to lack of imagination. A truly fascinating debate…like Darwin’s Evolution! Adrian Van Maanen claimed to see rotation (said he could see 0.1”/yr) 0.1”=1/(2x106) radians/yr so that’s D/ (2x106) =0.4 pc/yr=1.3 ly/year!! Faster than speed of light!! Impossible! Surmised Andromeda must be much closer, smaller, and inside MW. =r/D D(/t)=(r/t)

  7. Spiral Illusions Is this spiral nebula actually rotating? (This is M101, the “pinwheel” galaxy”). Does its form draw you to conclude it is? Shapley wrote to van Maanan: “Congratulations on the nebulous results! Between us we have put a crimp in the island universes, it seems, you by bringing the spirals in and I by pushing the Galaxy out. We are indeed clever, we are.”

  8. Spiral Illusions

  9. Question The pinwheel looked like it was rotating to me a) yes b) no

  10. Super/nova? A supernova suddenly appeared in Andromeda in 1885 (~5.6 mag, naked eye!). Inverse Square Law: LSN/ Lbarnard= (DSN/Dbarnard)2 bSN/ bbarnard If Andromeda at 800 kpc then… DSN/Dbarnard=800 kpc/1.8pc=4x105 , bSN/ bbarnard=40 LSN/ Lbarnard=5x1012 so LSN= 2x109 Lsun !!! Shapley could not imagine anything could be as bright as 2 billion Suns so DSN must be much smaller, inside MW, right?! Agnes Clarke, “a scale of magnitude such as the imagination recoils from contemplating”. Brighter one in 1895 in NGC 5253!

  11. Why do the Spiral Nebulae avoid the Plane of the MW? Map of Spiral Nebulae Shapley thought MW disk inhibited formation of nebulae. Curtis reasoned it was dust in the plane of the MW blocking outside light, thus Spiral Nebulae were well outside MW.

  12. Winner? Debate widely viewed a draw. Then along came Edwin Hubble…

  13. 100 inch (2.5m) Hooker Telescope--widely Considered most important telescope… Incredible engineering feat (90 tons) First light in Nov. 2, 1917, by George Hale Edwin Powell Hubble 1889-1953, Athlete, Rhodes Scholar, born in Missouri, basketball coach, lawyer, in WWI. 1917 PhD in astronomy, U Chicago, “Photographic Investigations of Faint Nebulae” 1919--went to Mt. Wilson, best telescopes “He was part of a select group in California that for several decades dominated astronomy’s discoveries in the far Universe because of its employment of the world’s largest and best Telescope.” In the fall of 1923, Hubble began a study of Andromeda, spotting two ordinary novae and a variable star…

  14. Observatories in the 20th Century

  15. Recall Cepheids: Giant, pulsating stars Light Curve of Cepheid Variable Long P Short P Sharp rise, Slow decline In ~1900 they could see Cepheids at ~ 1 Megaparsec (106 pc)=2x1011 au That’s about a million times further than parallax and Almost a trillion times the distance to the Sun or 3.2 million light years!

  16. The Most Important Star Edwin Hubble using the 100” on Mt. Wilson Discovered Cepheids in Andromeda (Var! upper right) starting with this one. Page from lab notebook. Saw that the period was 31 days and that its mean brightness was 4000 times fainter than Barnard’s star (18.65 mag). In paper claimed 130 platesx35 minutes/plate. At 2 good hrs per night, that’s 38 nights or ~75 nights due to weather on best telescopes!!

  17. How Far was Hubble’s Cepheid in Andromeda? Inverse Square Law: Dceph=Dbarnard* (bbarnard/ bceph)1/2(Lceph/Lbarnard)1/2 Lceph/Lbarnard= 104/4x10-4 =2.5x107 Dceph=1.8pc* (4x103)1/2 *(2.5x107)1/2=1.8pc*3x105=600kpc =1,800,000 ly. Much bigger than even Shapley’s 50 kpc= 160,000 ly diameter Milky Way! Andromeda must be outside MW!

  18. HUBBLE VS. HUBBLE: CEPHEIDS IN M31 IN THE NEAR-INFRARED WFC3 V1 PHAT HST Survey; Riess et al. 2012

  19. Resolution Hubble could eventually see the whole period-luminosity relation. Saw no Cepheids away from Andromeda so knew that Cepheids were inside Andromeda. Van Maanen resisted conceding, but Shapley did. Hubble hesitated leading to his paper being delayed and read at AAS. Curtis: “Recent results by Hubble make the theory doubly certain” Shapley: Said to Payne-Gaposhkin when letter arrived from Hubble, “Here is the letter that destroyed my Universe.” “I believed in van Maanen’s results…after all he was my friend.”

  20. From Hubble to Hubble (Space Telescope) ~9 mag= 4000 in brightness Same idea today with Cepheids 4000 times fainter, galaxies 60 times farther!! ~35 Mpc

  21. Using The Hubble Space Telescope;Cepheids to Supernovae

  22. Cepheids Variables,Period Indicates Luminosity, Tells Distance Anchor (NGC 4258): Galaxy with Cepheids whose distance we know by geometry Supernova Host: Galaxy with Cepheids and an SN Ia, former calibrates latter Using a “distance ladder” we knit together progressively longer range distance indicators to ~300 million light years

  23. Hubble Continued to Study Galaxies Increasing ratio of arms to nucleus Hubble’s Tuning Fork:A Tool to Classify Galaxies

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