What is the density of matter near the sun in a 1/r^2 case?

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SUMMARY

The density of matter near the Sun, assuming a 1/r^2 distribution, results in a constant Keplerian velocity for stars at varying radii. Specifically, the discussion establishes that if the density of matter in the galaxy decreases proportional to 1/r, the Keplerian velocity at a radius of 1000 parsecs is calculated to be 75 km/s. In contrast, under a 1/r^2 density model, the velocity remains constant regardless of the radius. The calculations utilize the formula v^2 = (GM/R) and M = (4/3 * π * R^3) * 1/R.

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The sun orbits the galaxy at 220 km/s at a distance of 8500 parsecs from the centre of the galaxy. If the density of matter in the galaxy drops off proportional to 1/r, what would be the Keplerian velocity of a star orbiting at a radius of 1000 parsecs? What would be the Keplerian velocity of that star if the density of matter in the galaxy drops proportional to 1/r2 ? What is the density of matter in the vicinity of the sun in this 1/r2 case?
 
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I have solved it using v^2=(GM/R)^1/2 and M=(4/3*3.14*R^3)1/R
If density is proportional to 1/r, the keplerian velocity at 1000 parsecs is 75km/s
And if the density is 1/r^2, then the speed is constant at all radiuses.
I Think this does make sense?
 

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