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

  • Thread starter Thread starter Bacilla
  • Start date Start date
  • Tags Tags
    Density Matter
Bacilla
Messages
7
Reaction score
0
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?
 
Physics news on Phys.org


show attempt to solution if you want to get some help, read and follow the forum rules.
 


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?
 

Thread 'Initial conditions for orbits around a wormhole'

Hi, I had an exam and I completely messed up a problem. Especially one part which was necessary for the rest of the problem. Basically, I have a wormhole metric: $$(ds)^2 = -(dt)^2 + (dr)^2 + (r^2 + b^2)( (d\theta)^2 + sin^2 \theta (d\phi)^2 )$$ Where ##b=1## with an orbit only in the equatorial plane. We also know from the question that the orbit must satisfy this relationship: $$\varepsilon = \frac{1}{2} (\frac{dr}{d\tau})^2 + V_{eff}(r)$$ Ultimately, I was tasked to find the initial...
View full post »

Thread 'Help to convert units of a simple formula'

The value of H equals ## 10^{3}## in natural units, According to : https://en.wikipedia.org/wiki/Natural_units, ## t \sim 10^{-21} sec = 10^{21} Hz ##, and since ## \text{GeV} \sim 10^{24} \text{Hz } ##, ## GeV \sim 10^{24} \times 10^{-21} = 10^3 ## in natural units. So is this conversion correct? Also in the above formula, can I convert H to that natural units , since it’s a constant, while keeping k in Hz ?
View full post »

Similar threads

Dark matter density in fucntion of radius
Replies
7
Views
3K
What Is the Density at the Center of the Sun?
Replies
2
Views
3K
B What keeps most galactic stars from falling into the centeral black hole?
Replies
6
Views
2K
What is the Mass of Dark Matter in a Spiral Galaxy?
Replies
4
Views
2K
What Is the Rate of Continuous Creation Needed to Maintain Universal Density?
Replies
4
Views
2K
I Questions regarding dark matter dynamics
2
Replies
65
Views
8K
Solving Binary Star Problems: Tips & Strategies
Replies
3
Views
2K
What is the evidence for dark matter in the solar neighborhood?
Replies
7
Views
2K
Stability of a White Dwarf Against Gravitational Collapse
Replies
3
Views
2K
B The Sun's Influence on the Moon's Orbit: Is it Negligible?
Replies
4
Views
2K

Hot Threads

Recent Insights

Back
Top