ORIGINS 2B03 Lecture Notes - Galaxy Rotation Curve

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turquoiseant391

9 Feb 2012

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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.

Related Questions

Here is the info about the question. what i just dontunderstand isin the dispersion equation, v-v_ave. I know to use theaverage velocities for v_ave 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 M_sun, sisin km/sec, and R is in Mpc.
s is the velocity dispersion: s={[sum(v-v_ave)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.

ceruleangiraffe295

(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.

pinkswan477

ORIGINS 2B03 Lecture Notes - Galaxy Rotation Curve

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