Dark Matter, calculating missing mass

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SUMMARY

The discussion focuses on calculating the missing mass of the Andromeda galaxy, which has a rotational velocity of 250 km/s and an observed mass of 1 x 1042 kg. The diameter of the galaxy is approximately 66,000 light years. Participants emphasize the need to apply the equations Fc=mv2/R and Fg=Gm1m2/R2 to determine the total mass and subsequently find the percentage of mass that is not visibly accounted for. The challenge lies in correctly interpreting the problem and applying the necessary calculations.

PREREQUISITES
  • Understanding of gravitational forces and centripetal motion
  • Familiarity with the equations Fc=mv2/R and Fg=Gm1m2/R2
  • Basic knowledge of angular velocity and tangential speed
  • Concept of mass distribution in celestial bodies
NEXT STEPS
  • Calculate the total mass of the Andromeda galaxy using the provided equations
  • Research the concept of dark matter and its implications in astrophysics
  • Explore the methods for measuring galactic mass and velocity
  • Learn about the assumptions of uniform density in celestial objects
USEFUL FOR

Astronomy students, astrophysicists, and anyone interested in understanding the dynamics of galaxies and the concept of dark matter.

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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