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 10^42 kg. Using the formulas Fc=mv²/r and Fg=Gm₁m₂/r², participants are guided to calculate the total mass, which includes both visible and invisible components. The key takeaway is that the calculated mass will exceed the observed mass, indicating the presence of dark matter. The method to find the percentage of missing mass involves comparing the calculated mass to the observed mass.

PREREQUISITES
  • Understanding of gravitational forces and centripetal motion
  • Familiarity with the formulas Fc=mv²/r and Fg=Gm₁m₂/r²
  • Basic knowledge of astronomical measurements, such as light years
  • Ability to perform algebraic calculations involving mass and velocity
NEXT STEPS
  • Calculate the total mass of the Andromeda galaxy using the provided formulas
  • Research the concept of dark matter and its implications in astrophysics
  • Explore the methods of measuring galactic rotation and mass distribution
  • Learn about the role of gravitational lensing in detecting invisible mass
USEFUL FOR

Astronomy students, astrophysicists, and anyone interested in understanding the concepts of dark matter and galactic dynamics.

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 and Fg=Gm1m2/r^2


The Attempt at a Solution



There was no answer, i know I am supposed to calculate the the velocity and its mass, then but to get the percent of mass missing i think you divide the difference between the the calculated mass and given mass by the calculated mass or something like that. But i am still rather confused at what to do. I am not looking for someone to complete my homework, just to help me understand how to do this question.
 
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But i am still rather confused at what to do.
Start with the part you described - calculate the mass with the formulas. It will be larger than 1042 kg, and this number is (visible mass)+(invisible mass). Can you calculate the invisible mass?
 

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