How Do I Calculate Galactic Mass Proportional to Radius?

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SUMMARY

The calculation of galactic mass as a function of radius is established through the equations M(r)=v²r/G and M(r)=vrc²/G, with the former being the correct formulation for determining mass based on velocity and radius. The velocity, v, can be derived from the flat rotation curve of the galaxy, allowing for the calculation of mass using M(r)=Mr/R, where M is the total mass and R is the radius. For tidal force calculations, the formula r=(d³m/(2MR))¹/² is used to determine the distance at which a star is tidally disrupted by a nearby galaxy, where m is the total mass of the galaxy containing the star, R is its radius, M is the mass of the nearby galaxy, and d is the distance between their centers.

PREREQUISITES
  • Understanding of Newton's law of gravitation
  • Familiarity with galactic dynamics and rotation curves
  • Knowledge of tidal forces in astrophysics
  • Proficiency in algebraic manipulation of equations
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  • Learn about the application of Newtonian gravity in astrophysical contexts
  • Explore tidal disruption events and their implications in galaxy interactions
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Astronomers, astrophysicists, and students studying galactic dynamics or tidal interactions in astrophysics will benefit from this discussion.

StephenPrivitera
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How do I calculate galactic mass as a function of r? I know it is supposed to be proportional to r. I've seen,
M(r)=v2r/G
And also I've seen
M(r)=vrc2/G
Which if any is right?
And what do I use for v?
Thanks so much for your help!
 
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The rotation curve is flat so I can find v by plugging in the radius and total mass of the galaxy. Doing that I get,
M(r)=Mr/R, where M is the total mass of the galaxy and R is the radius of the galaxy
I'm trying to do a tidal force calculation to see how far away from the center of a galaxy a star needs to be to be tidally disrupted by a nearby galaxy. I'm getting
r=(d3m/(2MR))1/2 where m is the total mass of the galaxy that the star lies in, R is the radius of that galaxy, M is the total mass of the nearby galaxy, and d is the distance between the two galactic centers. Can anyone verify this?
 

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