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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

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.

gathering views of the spiral nebulae
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!
question
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)

andromeda biggest spiral nebula central role
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?

the great debate
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).

the debate points

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)

spiral illusions
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.”

question1

Question

The pinwheel looked like it was rotating to me

a) yes b) no

super nova
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!

why do the spiral nebulae avoid the plane of the mw
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.

winner
Winner?

Debate widely viewed a draw.

Then along came Edwin Hubble…

edwin powell hubble

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…

slide15

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!

the most important star
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!!

how far was hubble s cepheid in andromeda
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!

resolution
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.”

from hubble to hubble space telescope
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

cepheids variables period indicates luminosity tells distance
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

hubble continued to study galaxies
Hubble Continued to Study Galaxies

Increasing ratio of arms to nucleus

Hubble’s Tuning Fork:A Tool to Classify Galaxies