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ORIGINS 2B03 Lecture Notes - Galaxy Rotation Curve

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turquoiseant391
9 Feb 2012
School
McMaster University
Department
Origins
Course
ORIGINS 2B03
Professor
Laura Parker

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Document Summary

Most of the universe is made up of something we don"t know (dark matter) 1933, fritz zwicky made the first estimates of the masses of clusters of galaxies w/o extra mass the galaxies would have velocities too high to stay in clusters. He measured the speeds of galaxies, then through the speeds found the mass of the whole galaxy, then compared that mass to the visible luminous mass of the galaxy which was much smaller than the whole galaxy cluster"s mass! What did zwicky find? (total mass)/(mass in stars + gas) = few hundred. There is some mass that we cannot see in these clusters. Speed of rotation can tell us the mass of the objects. Speed of rotation can be measured using spectrum lines. Your only sensitive to the mas on the inside. The circular velocity in the disk goes up and as you go further out velocity is constant.

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Related Questions

Here is the info about the question. what i just dontunderstand isin the dispersion equation, v-vave. I know to use theaverage velocities for vave obviously,but what value isto be used for v?

Assume that the galaxy cluster of question 2 has a radius of 1Mpc(=3 x 1022 m). What is its mass?
Hints: use the virial equation s2 = GM/R = 4.5x10-9 M/R, where M is expressed in Msun, sisin km/sec, and R is in Mpc.
s is the velocity dispersion: s={[sum(v-vave)2]/(N-1)}1/2

Galaxy Name Redshift (km/sec)
G001 1915
G002 953
G003 2741
G004 1095
G005 2178
G006 2630
G007 1245

fyi: here is question 2:
A galaxy cluster contains the galaxies listed in the tablebelow.What is the distance to this cluster?

Galaxy Name Redshift (km/sec)
G001 1915
G002 953
G003 2741
G004 1095
G005 2178
G006 2630
G007 1245
i got 25 mpc for the distance.

The great astronomer Edwin Hubble discovered that all distant galaxies are receding from our Milky Way Galaxy with velocities proportional to their distances. It appears to an observer on the Earth that we are at the center of an expanding universe. Figure 3.64 illustrates this for five galaxies lying along a straight line, with the Milky Way Galaxy at the center. Using the data from the figure, calculate the velocities: (a) relative to galaxy 2 and (b) relative to galaxy 5. The results mean that observers on all galaxies will see themselves at the center of the expanding universe, and they would likely be aware of relative velocities, concluding that it is not possible to locate the center of expansion with the given information.

Figure 3.64 Five galaxies on a straight line, showing their distances and velocities relative to the Milky Way (MW) Galaxy. The distances are in millions of light-years (Mly), where a light-year is the distance light travels in one year. The velocities are nearly proportional to the distances. The sizes of the galaxies are greatly exaggerated; an average galaxy is about 0.1 MlY across.

The great astronomer Edwin Hubble discovered that all distant galaxies are receding from our Milky Way Galaxy with velocities proportional to their distances. It appears to an observer on the Earth that we are at the center of an expanding universe. The figure illustrates this for five galaxies lying along a straight line, with the Milky Way Galaxy at the center. Using the data from the figure, calculate the velocities:

(a) relative to galaxy 2 and

(b) relative to galaxy 5.

The results mean that observers on all galaxies will see themselves at the center of the expanding universe, and they would likely be aware of relative velocities, concluding that it is not possible to locate the center of expansion with the given information.