Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller
description
Transcript of Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller
![Page 1: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/1.jpg)
Astronomy 2
Overview of the Universe
Spring 2007
11. Lectures on External Galaxies.
Joe Miller
![Page 2: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/2.jpg)
Are the “spiral nebulae” extragalactic? Or, do we live in the only galaxy in the universe? The age-old astronomy problem: distance.
![Page 3: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/3.jpg)
April 1920: the Curtis-Shapely debate
Shapely (Harvard): Argued that spiral nebulae were inside our galaxy for several reasons
• Galaxy was huge (he didn’t know about dust).
• van Maanen’s observations showed that one spiral nebula, M 101, could be observed to rotate. It it were outside our galaxy, it would have to be turning faster than the speed of light.
• Spiral nebulae were never seen in the Milky Way: the “zone of avoidance.” Therefore, their distribution acknowledged the geometry of our galaxy, and they must be part of our galaxy.
• A nova, S Andromeda, was observed in the Andromeda Nebula. If this nebula were outside our galaxy, the nova would have to be incredibly bright, much brighter than known novae.
![Page 4: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/4.jpg)
Curtis-Shapely debate (cont.)
Curtis (Lick): Argued that the spiral nebulae were other galaxies, well outside our own galaxy:• van Maanen must have made errors in his measurements of M101, and
it wasn’t rotating.• The zone of avoidance must be an artifact of something in our galaxy-
perhaps dust extinction- blocking our view of galaxies in the Milky Way.
• S Andromeda was not a normal nova. It was something else, something much brighter.
• Slipher’s observations of several spiral nebulae showed that they had large red Doppler shifts, indicating they were moving away from us at very high speeds, speeds too high to be a part of our galaxy.
Shapely had the strongest arguments, but Curtis was right!
![Page 5: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/5.jpg)
![Page 6: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/6.jpg)
Edwin Hubble completely settled the controversy.
He found a Cepheid variable star in M 31, the Andromeda galaxy. The period-luminosity relationship for Cepheids defines a close relationship between the period of pulsation and the absolute magnitude of the star. Sine the apparent magnitude can be measured directly, determining the period of a Cepheid variable gives a precise measurement of its distance. Using present-day data, it is about 700,000 pc from us. It can be seen with the naked eye.
![Page 7: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/7.jpg)
![Page 8: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/8.jpg)
The universe is teeming with galaxies
M 31: nearest example of a large galaxy.
Has all the same components that are found in our galaxy: globular star clusters, halo and disk stars, young star clusters, dust, gas, etc.
Literally billions of galaxies can be recorded on images with large modern telescopes. The vast majority are much further away than M 31, and once again measuring distances is a major problem.
![Page 9: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/9.jpg)
The Realm of the Galaxies
The variety is enormous, and our understanding of what is going on is a
work in progress!
![Page 10: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/10.jpg)
![Page 11: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/11.jpg)
![Page 12: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/12.jpg)
![Page 13: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/13.jpg)
![Page 14: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/14.jpg)
![Page 15: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/15.jpg)
![Page 16: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/16.jpg)
![Page 17: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/17.jpg)
![Page 18: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/18.jpg)
Hubble’s “tuning fork” diagram.
![Page 19: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/19.jpg)
Distances to galaxies
![Page 20: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/20.jpg)
Measuring distance to galaxies:
1) Out to 10 million pc (~30 million with HST): Cepheids, O and B stars, supergiants.
2) Tully-Fisher relationship: (100 million pc)There is a relationship between the line width of a galaxy in neutral hydrogen radiation, which measures rotation speed of a galaxy, which is a measure of its mass, and the luminosity of the galaxy. This works for spirals.
3) supernovae: billions of pc (appear to be quite good).
4) redshifts- a great discovery!
![Page 21: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/21.jpg)
![Page 22: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/22.jpg)
The expanding universe: Hubble’s great discovery
The farther away a galaxy is from us, the faster it is moving away from us. Since motion away from us produces a Doppler shift toward the red, it is equivalent to say that the redshifts of galaxies increase with distance.
![Page 23: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/23.jpg)
The Hubble diagram:
![Page 24: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/24.jpg)
This does not mean we are at the center of the universe. The entire universe is expanding, so the distance between all galaxies is increasing (except ones close enough to be bound together by gravity). If we lived in another distant galaxy, we would see all galaxies moving away from us.
![Page 25: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/25.jpg)
The Hubble Constant
The Hubble constant H0 is the slope of the line in the Hubble diagram. It is the rate of expansion, and the subscript “0” means the present value of the constant. The universe could change its rate of expansion.
One current value for the Hubble constant is around
H0 = 73 km/sec/Mpc
with an uncertainty of plus or minus about 5 km/sec/Mpc. This means that outward velocities of galaxies increase 73 km/sec for every Mpc (million pc) of increasing distance.
![Page 26: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/26.jpg)
Using redshifts to derive distances:
Since the Hubble constant H0 is the slope of the line in the Hubble diagram, we can write
Example:
If v = 6500 km/sec, then 6500/65 = 100 Mpc. An object with a redshift corresponding to a velocity of 6500 km/sec would be 100 million pc away.
c(Δλλ
) =v=H0d, where d is in Mpc. Therefore
d=vH0
![Page 27: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/27.jpg)
Rotation of our galaxy allows mass determination
![Page 28: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/28.jpg)
![Page 29: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/29.jpg)
Masses of galaxies- a dark mystery. Dark matter.
![Page 30: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/30.jpg)
It now appears that there is about 10 times as much dark matter as ordinary matter! What it is remains a mystery, but many think it is some kind of as yet undiscovered elementary particle.
![Page 31: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/31.jpg)
Galaxies often come in groups, ranging from a few members to 1000’s of galaxies.
![Page 32: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/32.jpg)
The Local Group- a small cluster
![Page 33: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/33.jpg)
![Page 34: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/34.jpg)
![Page 35: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/35.jpg)
![Page 36: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/36.jpg)
The building up of galaxies through merging
![Page 37: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/37.jpg)
![Page 38: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/38.jpg)
![Page 39: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/39.jpg)
![Page 40: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/40.jpg)
![Page 41: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/41.jpg)
![Page 42: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/42.jpg)
![Page 43: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/43.jpg)
![Page 44: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/44.jpg)
![Page 45: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/45.jpg)
![Page 46: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/46.jpg)
Additional evidence for dark matter:
Gravitational lensing
![Page 47: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/47.jpg)
![Page 48: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/48.jpg)
![Page 49: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/49.jpg)
![Page 50: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/50.jpg)
![Page 51: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/51.jpg)
Once again, the amount of dark matter needed to make these lenses work is about 10 times the visible matter. The dark matter is not distributed exactly the same as the visible light.
![Page 52: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/52.jpg)
Radio astronomy: the discovery of radio galaxies, active galaxies, and quasars.
![Page 53: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/53.jpg)
![Page 54: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/54.jpg)
![Page 55: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/55.jpg)
![Page 56: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/56.jpg)
![Page 57: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/57.jpg)
Finally, a radio star is found!
![Page 58: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/58.jpg)
![Page 59: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/59.jpg)
Surprising result: this star is traveling away from us at roughly 16% of the speed of light!!!
![Page 60: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/60.jpg)
Major discovery: 3C 273 is found to vary significantly in light output in days! It can’t be more than a few light days in size.
Extreme energy generation from a very compact region or new physics to explain
the redshifts.
![Page 61: Astronomy 2 Overview of the Universe Spring 2007 11. Lectures on External Galaxies. Joe Miller](https://reader036.fdocuments.in/reader036/viewer/2022070403/5681399c550346895da1363b/html5/thumbnails/61.jpg)