Calculating mass of Milky way Galaxy

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    Galaxy Mass Milky way
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Discussion Overview

The discussion revolves around calculating the mass of the Milky Way Galaxy using the formula ##v^2 = MG/R##, where participants explore the implications of their calculations and the correct application of units and constants.

Discussion Character

  • Mathematical reasoning
  • Technical explanation
  • Homework-related

Main Points Raised

  • One participant initially calculates the mass using given values for velocity, gravitational constant, and radius but expresses confusion over the result.
  • Another participant points out a missing factor in the numerator and questions the origin of a specific value in the denominator.
  • A later reply acknowledges a mistake in unit conversion and recalculates the mass, arriving at a new value.
  • Another participant suggests checking the math and provides an alternative calculation, arriving at a significantly different mass estimate.
  • One participant expresses gratitude for the assistance but does not confirm the accuracy of the revised calculations.

Areas of Agreement / Disagreement

The discussion contains multiple competing views regarding the calculations, with no consensus on the correct mass value for the Milky Way Galaxy. Participants express uncertainty and challenge each other's calculations without reaching a definitive conclusion.

Contextual Notes

Participants mention unit conversions and the importance of scientific notation, indicating potential limitations in their calculations. Specific assumptions about the values used and their transformations are not fully resolved.

Who May Find This Useful

This discussion may be useful for individuals interested in astrophysics, particularly those exploring methods for calculating galactic masses and the implications of unit conversions in such calculations.

RyanH42
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I used the ##v^2=MG/R## to calculate mass of milky way.Now ##v=225000## m/s G=6.7 10-11 and r is 16 kpc source (https://upload.wikimedia.org/wikipedia/commons/7/77/Rotation_curve_(Milky_Way).JPG)
If I plut them I get ##50,625,000,000=v^2## and the other side G=6.6 10-11 and R =49.6 1019 so ##M=v^2R/G## that's equal 50,625,000,000/5.1020.6.6 10-11 which its ≅ 1.534 10-3

Whats the point which I am missing
 
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RyanH42 said:
Whats the point which I am missing

You forgot to include R in the numerator of your calculation, and I don't understand where the 5.1020 in the denominator comes from.
 
Oh I made a huge mistake now I see it 5 1020 comes from kpc-meter transformation.Then the answer will be 50,625 106*5 1020/6.6 10 -11.Which we get ≅40 10 36 which means 8 106 Msun
 
But again it false
 
RyanH42 said:
But again it false

Check your math. I get as a rough answer ##\left( 5 \times 10^{10} \right) \left( 5 \times 10^{20} \right) / \left( 7 \times 10^{-11} \right)##, which comes out to about ##4 \times 10^{41}##, or about ##10^{11} M_{sun}##, which is about right. (As a rule of thumb, when using scientific notation, always adjust the exponent so that the number in front is between 1 and 10. You didn't do that for the ##v^2## factor and I think it confused you.)
 
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Probably you are right.Thanks for help
 

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