Vanderwall Sean Cosmology Problem Set 5 November 2, 2006 Problems: HW 5: 20.38, 20.48, 21.35, 21.42. 20.38 a) Galaxy NGC 4594 is classified as a Sa galaxy because it is a very spherically based spiral galaxy with an extremely large bulge and has a disk that has retained a fair amount of dust in its spiral arms, but is still very tight and the disk does not extend very far outwards. b) Galaxy NGC 6744 is classified as a Sc galaxy because it has a very centralized, but small spherical center, and also contains long spiral arms that are made up of a number of stars and a very large amount of dust. c) Galaxy NGC 4414 is classified as a Sb galaxy because it has a bit tighter spiral arms compared to that of NGC 6744, but not as tight as NGC 4594. The bulge is fairly large, but not over-dominant with respect to the rest of the galaxy; and the amount of dust in the outer disk is condensed somewhat towards the center, yet still retains its large-disked characteristics. d) Galaxy NGC 1300 is classified as a SBb galaxy because it is a barred spiral galaxy with a semi-large bulge and tightly wound spiral arms. It can be considered this SBb form of galaxy also because the spiral arms are relatively close to the barred portion of the galaxy, while they also retain a good amount of stellar dust. e) Galaxy M 87 is classified as an E0 galaxy because it is an extremely huge elliptical galaxy with a very round center and is very large in its composition. 20.48 a) Redshifts Galaxy 1: 659.6 656.3/656.3 = .0050 Galaxy 2: 664.7 656.3/656.3 = .0128 Galaxy 3: 679.2 656.3/656.3 = .0349 b) Speed Galaxy 1: (3 x 105) x .0050 = 1500 km/s or .5% of the speed of light. Galaxy 2: (3 x 105) x .0128 = 3840 km/s or 1.3% the of speed of light. Galaxy 3: (3 x 105) x .0349 = 10,470 km/s or 3.5% of the speed of light.
21.35 An elliptical galaxy, when it is young, is made up of a number of stars. Some of these stars are young and some of these stars are older. The young stars in the galaxy have a very bluish-white color and shine immensely bright and hot. The older stars are much dimmer and have a red color because they are colder. Because of this, a person who is looking at the galaxy would see the bright blue and white color because the young stars would be overpowering the older ones. As the galaxy gets older, so do the stars and the young stars begin to transfer into older and colder stars. The galaxy would soon become very red and not very bright, until finally the stars have burnt out. 21.42 The galaxy M 82 should live for about 100 million years longer or so. Over this stretch of time, the galaxy's appearance will change due to not only the age of the stars in the galaxy, but also due to the lack of high star formation. With the extreme formation of new stars, The galaxy is constantly firing out large amounts of hot gas, which to the visible eye have a red color. And with all of the new stars that have been formed, the galaxy contains a very distinct bluish-white disk. Without new stars forming from the galaxy, there would be no more hot red gas exploding from the center. And with all of the gas used up to form the stars, not only would there be no more young stars, and thus create a redder tint to the galaxy, but there would be no dusk in the disk, just a number of stars that are getting older, almost as if there were no galaxy at all, but instead just a cluster of stars around a centralized base.