Dark Matter, calculating missing mass

AI Thread Summary
The discussion focuses on calculating the missing mass of the Andromeda galaxy, which has a rotation velocity of 250 km/s and an observed mass of 1 x 10^42 kg. Participants highlight the need to apply gravitational and centripetal force equations to determine the total mass and identify the discrepancy between observed and calculated mass. There is uncertainty about whether to assume a uniform density for the galaxy in the calculations. The original poster expresses frustration over not being able to solve the problem and seeks assistance. The conversation emphasizes the complexities involved in calculating dark matter and the importance of clear problem parameters.
cherioslover
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Homework Statement


The andromeda galaxy has a velocity of 250 km/s as it rotates. The observed mass is 1 x 10^42 kg. If the galaxy is roughly a circle with a diameter of 66,00 light years how much mass is not accounted for visibly?


Homework Equations



Fc=mv^2/R Fg=Gm1m2/R^2

The Attempt at a Solution



I know you're supposed to calculate the mass of the galaxy as well as a calculated speed, then divide the differences in masses by gravitational mass to find the percentage of mass missing, but honestly i can't seem to get it and there was no answer given :(

someone pleas be my hero :')
 
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cherioslover said:

Homework Statement


The andromeda galaxy has a velocity of 250 km/s as it rotates. The observed mass is 1 x 10^42 kg. If the galaxy is roughly a circle with a diameter of 66,00 light years how much mass is not accounted for visibly?


Homework Equations



Fc=mv^2/R Fg=Gm1m2/R^2

The Attempt at a Solution



I know you're supposed to calculate the mass of the galaxy as well as a calculated speed, then divide the differences in masses by gravitational mass to find the percentage of mass missing, but honestly i can't seem to get it and there was no answer given :(

someone pleas be my hero :')
Can you give us the exact wording of the problem?

If the question is stating that the mass on the outer edge of the galaxy is moving at a tangential speed of 250 km/sec, then you can work out the angular speed of the outer mass.

Does the problem state that you should assume that the galaxy is a disc of uniform density?

AM
 
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