AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.
-
Upload
leonard-jackson -
Category
Documents
-
view
218 -
download
1
Transcript of AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.
![Page 1: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/1.jpg)
AST101Lecture 20
The Parts of the Galaxy
![Page 2: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/2.jpg)
Shape of the Galaxy
![Page 3: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/3.jpg)
Constituents of the Galaxy
~4 x 1011 stars (90% of the visible mass)• Disk population (population I)
– Younger stars– Higher metallicity– Orbits in plane of Galaxy
• Spheroidal population (population II)– Older stars– Lower metallicity– Randomly-directed orbits– Globular Clusters
![Page 4: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/4.jpg)
Globular Cluster
• About 1010 years old
• 105 - 106 stars• Radius ~ 10 light
years• Most massive
star: ~ 1 solar mass• ~150 globular
clusters known in Milky Way
![Page 5: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/5.jpg)
Age and Location
• The oldest population is the halo (including the globular clusters)
• The bulge is also old
• The disk is youngest
The age is correlated with flatness
The Sun is in the disk
![Page 6: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/6.jpg)
Constituents of the Galaxy
Gas and dust (10% of the visible mass)• Interstellar medium:
– Warm 104K to hot 106K– Low density: 0.01 - 1 H/cm3
• Molecular clouds: – Cold: <100K– Dense: 103-104 H/cm3
~1% dust-to-gas ratio.Dust: mostly carbon and silicates
![Page 7: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/7.jpg)
Barnard 163
dark cloud
![Page 8: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/8.jpg)
![Page 9: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/9.jpg)
Evidence for the ISM• We see absorption by dark clouds• We see absorption lines in the spectra of
stars• We see emission from Hydrogen• Distant stars are fainter and redder than
expected
The ISM attenuates starlight by about 1 magnitude every 3000 light years
![Page 10: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/10.jpg)
Reddening Illustrated
![Page 11: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/11.jpg)
Red, Reddening, Redshifted
• Red: a color. Red stars are cooler than blue stars (remember the blackbody)
• Reddening: the effect of interstellar absorption. Dust absorbs/scatters blue light more than red light. The reason the sky is blue.
• Redshift: Doppler shift from a source moving away
![Page 12: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/12.jpg)
The Neighborhood
![Page 13: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/13.jpg)
Charting the Galaxy
![Page 14: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/14.jpg)
![Page 15: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/15.jpg)
Gas and Dust in the IR
![Page 16: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/16.jpg)
Hydrogen in the Galactic Plane
![Page 17: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/17.jpg)
The 21 cm line of Hydrogen• Hydrogen is
abundant (90% of all atoms)
• Radio waves penetrate gas and dust
• Velocities let us map out location of H in the Galaxy
![Page 18: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/18.jpg)
Spiral Arms
An effervescent phenomenon
![Page 19: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/19.jpg)
Spiral Density Waves
![Page 20: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/20.jpg)
Spiral Arms
Marked by:
• Pileup of gas and dust
• Star formation due to increased densities
• Bright young stars
Inter-arm regions: uniform density of stars
![Page 21: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/21.jpg)
Meet the Neighbors
![Page 22: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/22.jpg)
Large Magellanic Cloud
![Page 23: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/23.jpg)
How the Milky Way Was Built
The Sagittarius Dwarf Galaxy
![Page 24: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/24.jpg)
Orbit of the Sgr Dwarf Galaxy
![Page 25: AST101 Lecture 20 The Parts of the Galaxy. Shape of the Galaxy.](https://reader036.fdocuments.net/reader036/viewer/2022062519/5697c0241a28abf838cd4c5d/html5/thumbnails/25.jpg)
Galactic Cannibalism