Acceleration due to gravity in a galaxy?

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Discussion Overview

The discussion revolves around the acceleration due to gravity at the periphery of a galaxy, exploring how it can be calculated and the factors involved in such calculations. Participants reference both theoretical and practical aspects of this topic, including gravitational equations and estimations based on galaxy mass and distance.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Exploratory

Main Points Raised

  • One participant asks about the strength of acceleration due to gravity at the periphery of a galaxy, indicating a desire for specific numerical values.
  • Another participant provides links to Wikipedia articles on galaxy rotation curves, suggesting these resources for further understanding.
  • A participant outlines the necessary parameters for calculating gravitational acceleration, including distance from the galaxy center, total mass within that radius, and the gravitational constant.
  • One participant suggests using a specific formula involving the mass of the galaxy and distance to estimate gravitational acceleration, providing an example calculation that yields approximately 0.4 nanometers per second squared.
  • A later reply expresses surprise at the simplicity of the gravitational equation compared to Einstein’s Field Equation, while also questioning the estimated number of stars in a galaxy.
  • Another participant presents a calculation using the mass of the galaxy and distance in meters, arriving at a specific numerical result.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the exact values or methods for calculating gravitational acceleration at the periphery of a galaxy. There are differing views on the complexity of the equations involved and the estimated number of stars in a galaxy.

Contextual Notes

Participants mention various assumptions, such as the mass of the galaxy and the distance used in calculations, which may affect the results. There is also uncertainty regarding the number of stars in a typical galaxy and the applicability of different gravitational equations.

Bjarne
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How strong is acceleration due to gravity ?
For example at the periphery at a galaxy ?
 
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To determine the acceleration due to gravity at the periphery of a galaxy, you need to know three numbers. The first is the distance from the galaxy centre where your acceleration is to be calculated (the radius). The second is the total mass of the galaxy contained with that radius. The third is the gravitational constant, G.

Lastly, you will need to learn about Newton's law of gravity (the wikipedia article is suffucient). With the above three numbers, some knowledge of how gravity works and a little bit of calculating, you should be able to work the numbers out yourself.
 
Bjarne said:
How strong is acceleration due to gravity ?
For example at the periphery at a galaxy ?

Put this into google "G*(mass of sun)/(1 AU)^2"
without the quotes
The google calculator will tell you the accel due to sun's mass at the Earth's usual distance of 1 AU.The distance from center to apparent edge is sometimes estimated
about 15,000 parsecs. The mass of our galaxy within that radius has been put at 700 billion solar masses. Try this in the google search window, without the quotes:

"G*(700*10^9 mass of sun)/(15 kpc)^2"

I think you will get around 0.4 nanometer per second per second.
 
Last edited:
Thank's

PS..
1.) I thought the equation was more complicated (Einstein’s Field Equation). But I assume GM/r^2 can be used as a rough estimation (?).
2.) I thought there are “only" 200 stars” in a typical galaxy (not 700 ?)
3.) 15,000 parsecs = 4,62e20 Meter (50.000 LY )

700e9*2e30*6,67E-11/4,62e20^2= 4,37e-10 M^2
 

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