Figure 2 shows the “"rotation curve" of NGC 2742. It plots the “radial velocity (V)" (how fast material is moving either toward or away from us) that is measured for objects at different distances (R = "radius") from the center of the galaxy. The center of the galaxy is at 0 kpc (kiloparsecs) with a speed of 9 km/sec away from us. (These velocities have been corrected for the observed tilt of the galaxy and represent true orbital velocities of the stars and gas.) 200 100 U4779 -100 As you can see, one side of the galaxy is moving with a negative velocity (spinning toward us), while the other side has a positive velocity (spinning away from us). Using´ Newton's gravity equation, we will be able to determine the gravitational mass of the entire galaxy and how the mass varies versus distance from the galaxy's center. -200 -8 8 Radius (kpc) Read the following text carefully and follow the instructions: Select five radii spaced evenly from 0-10 kpc across the galaxy. Your selections should all be either on the 1) left (blueshifted) or right (redshifted) side of the galaxy. Record those radii in Table 1 using units of kpc. 2) Using the rotation curve (Fig. 2), determine the approximate orbital velocity (V) at each of your radii (R). Don't worry about the precise data points, just use the general trend to find the velocity at each of your radii. Record those values in Table I using units of km/s. 3) present within each radius to make the stars move at the measured speeds. Use Newton's law of gravity to calculate the mass vs. radius: Mgrav=RV²/G, where M should be quoted in solar masses (Msun). Remember to use MKS units for your calculations. Record your results in the “gravitational mass (Mgraw)" column in Table 1. Your numbers will be large (between 10° to 10'' Msun) because galaxies contain a lot of stars! Orbital velocity (part 2) and radius (part 1) can be used to calculate the "gravitational mass" that must be Radial Velocity (km/s)
Figure 2 shows the “"rotation curve" of NGC 2742. It plots the “radial velocity (V)" (how fast material is moving either toward or away from us) that is measured for objects at different distances (R = "radius") from the center of the galaxy. The center of the galaxy is at 0 kpc (kiloparsecs) with a speed of 9 km/sec away from us. (These velocities have been corrected for the observed tilt of the galaxy and represent true orbital velocities of the stars and gas.) 200 100 U4779 -100 As you can see, one side of the galaxy is moving with a negative velocity (spinning toward us), while the other side has a positive velocity (spinning away from us). Using´ Newton's gravity equation, we will be able to determine the gravitational mass of the entire galaxy and how the mass varies versus distance from the galaxy's center. -200 -8 8 Radius (kpc) Read the following text carefully and follow the instructions: Select five radii spaced evenly from 0-10 kpc across the galaxy. Your selections should all be either on the 1) left (blueshifted) or right (redshifted) side of the galaxy. Record those radii in Table 1 using units of kpc. 2) Using the rotation curve (Fig. 2), determine the approximate orbital velocity (V) at each of your radii (R). Don't worry about the precise data points, just use the general trend to find the velocity at each of your radii. Record those values in Table I using units of km/s. 3) present within each radius to make the stars move at the measured speeds. Use Newton's law of gravity to calculate the mass vs. radius: Mgrav=RV²/G, where M should be quoted in solar masses (Msun). Remember to use MKS units for your calculations. Record your results in the “gravitational mass (Mgraw)" column in Table 1. Your numbers will be large (between 10° to 10'' Msun) because galaxies contain a lot of stars! Orbital velocity (part 2) and radius (part 1) can be used to calculate the "gravitational mass" that must be Radial Velocity (km/s)
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Transcribed Image Text:Figure 2 shows the "rotation curve" of
NGC 2742. It plots the “radial velocity
(V)" (how fast material is moving
either toward or away from us) that is
measured for objects at different
distances (R = radius") from the
center of the galaxy. The center of the
galaxy is at 0 kpc (kiloparsecs) with a
speed of 9 km/sec away from us.
(These velocities have been corrected
for the observed tilt of the galaxy and
represent true orbital velocities of the
stars and gas.)
200
100
U4779
-100
As you can see, one side of the galaxy
is moving with a negative velocity
(spinning toward us), while the other
side has a positive velocity (spinning
away from us). Using Newton's
gravity equation, we will be able to
determine the gravitational mass of the
entire galaxy and how the mass varies
versus distance from the galaxy's center.
-200
-8
8
-4
Radius (kpc)
Read the following text carefully and follow the instructions:
Select five radii spaced evenly from 0-10 kpc across the galaxy. Your selections should all be either on the
1)
left (blueshifted) or right (redshifted) side of the galaxy. Record those radii in Table 1 using units of kpc.
2)
Don't worry about the precise data points, just use the general trend to find the velocity at each of your radii. Record
those values in Table I using units of km/s.
Using the rotation curve (Fig. 2), determine the approximate orbital velocity (V) at each of your radii (R).
3)
present within each radius to make the stars move at the measured speeds. Use Newton's law of gravity to calculate
the mass vs. radius: Mgrav =RV/G, where M should be quoted in solar masses (Msun). Remember to use MKS units
for your calculations. Record your results in the “gravitational mass (Mgraw)" column in Table 1. Your numbers will
be large (between 10° to 10'' Msun) because galaxies contain a lot of stars!
Orbital velocity (part 2) and radius (part 1) can be used to calculate the "gravitational mass" that must be
Table 1. Measurements from the Rotation Curve of NGC 2742
Radius Rotational Velocity gravitational mass Mgrav Luminosity
(Lsum)
mass/light ratio
Mgrav/Mium
luminous mass
(кре)
(km/s)
(in units of Msun)
Mum (in units of Msun)
Radial Velocity (km/s)
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