How Do Objects Move Near the Galactic Center?

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Discussion Overview

The discussion revolves around the movement of objects near the galactic center, particularly focusing on the dynamics of the solar system's orbit around the Milky Way's supermassive black hole, Sagittarius A*. Participants explore concepts of velocity, acceleration, and the nature of orbits in a galactic context, as well as broader cosmological implications related to the universe's expansion.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants inquire about the velocity and acceleration of objects falling towards the galactic center, questioning whether they follow fixed radial orbits like planets around the sun.
  • One participant suggests that gravity causes acceleration and proposes that the galaxy is spiraling towards the center of the universe, although this is later clarified to mean the center of the galaxy.
  • Another participant emphasizes that the solar system's orbit around the galactic center follows the same physical laws as planetary orbits, but raises questions about the nature of this motion.
  • There is a discussion about the spiral structure of galaxies, with some participants proposing that it results from density waves rather than a vortex-like motion.
  • Some participants express confusion regarding the concept of a central point in the universe, with one asserting that every observer perceives themselves as being at the center of the universe.
  • There are claims that the universe is expanding uniformly, with no specific center, which is challenged by others who suggest that a region of expansion could exist.
  • One participant mentions the relationship between entropy and the perception of time, suggesting that all points in time exist simultaneously.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the nature of motion near the galactic center and the implications of cosmological theories. There is no consensus on the existence of a central point in the universe or the interpretation of the universe's expansion.

Contextual Notes

Some statements rely on specific assumptions about gravitational dynamics and cosmological models that remain unresolved. The discussion includes various interpretations of the Big Bang Theory and the nature of galactic motion, which may depend on differing definitions and perspectives.

Slag
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Quick questions for you astrophysicists out there:

At what velocity do objects typically "fall" towards the galactic center? Or are we talking a positive acceleration? Assuming the sun were to survive long enough to reach the center, which it of course won't, how long would it take? Or do galactic objects remain in a fixed radial orbit like planets around the sun?

Any help is appreciated...

-Slag, FNG
 
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At what velocity do objects typically "fall" towards the galactic center? Or are we talking a positive acceleration?
The main theory is that we are spiraling tward the center of the universe.
Gravity itself causes acceleration.
 
So are we *not* moving towards the galactic center?
 
The solar system orbiting the galactic center is based on the same laws of physics as the Earth orbiting the sun.
 
Originally posted by Slag
Quick questions for you astrophysicists out there:

At what velocity do objects typically "fall" towards the galactic center? Or are we talking a positive acceleration? Assuming the sun were to survive long enough to reach the center, which it of course won't, how long would it take? Or do galactic objects remain in a fixed radial orbit like planets around the sun? *SNIP
Perhaps you could work it out yourself?

Inputs (these may not be the best values, but they'll do for now):
- distance of the solar system to Sag A* (the supermassive black hole at the centre of the Milky Way): 28,000 light years
- time taken for solar system to go once around Sag A*: 250 million years

Will the Sun 'fall' into Sag A*? Why should it? After all, the Earth doesn't 'fall' into the Sun :smile:
 
Copy. I'm no astrophysicist (hense why I'm asking such questions here) and have never claimed to be. I was always under the impression that the galaxy was slowly pulling into the "Sag A*" black hole. Perhaps I let the "whirlpool" shape of the spiral galaxy bias my views in this regard.

Thanks for the help...
 
Originally posted by Slag
Copy. I'm no astrophysicist (hense why I'm asking such questions here) and have never claimed to be. I was always under the impression that the galaxy was slowly pulling into the "Sag A*" black hole. Perhaps I let the "whirlpool" shape of the spiral galaxy bias my views in this regard.

Thanks for the help...
The spiral shape of some galaxies has been an active area of astronomical research for nearly a century! Suffice it to say that the stars in a (spiral) galaxy travel round the centre of the galaxy in nice, Newtonian-looking orbits - relatively small eccentricity ellipses (some caveats: they also bob 'up' and 'down' around the plane of the galactic disk; motions of stars in interacting/colliding galaxies are much different!). The clouds of gas and dust (giant molecular clouds) aren't so lucky! They are frequently disrupted, by collisions with other such clouds, by evaporation from nearby hot stars, by shock fronts from supernovae, and so on.

You've probably heard of barred spirals. It may be that the bar is important for keeping the central black hole well fed!
 
Thanks, Nereid!

I assume the "spiral" structure is due to the difference in angular velocity as the distance from the center increases, then? More of a "twisting" effect than the "vortex" I was previously assuming?
 
spirals are density waves

There are still quite a few mysteries regarding the spiral patterns, for example.

However, the main idea is that the spiral arms are density waves. Take a gander at these two sites:
http://nrumiano.free.fr/Egalax/spirals.html
http://www-astronomy.mps.ohio-state.edu/~pogge/Ast162/Unit4/spirals.html

or google on 'spiral galaxy density wave' ...
 
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  • #10


Originally posted by Nereid
There are still quite a few mysteries regarding the spiral patterns, for example.

However, the main idea is that the spiral arms are density waves. Take a gander at these two sites:
http://nrumiano.free.fr/Egalax/spirals.html
http://www-astronomy.mps.ohio-state.edu/~pogge/Ast162/Unit4/spirals.html

or google on 'spiral galaxy density wave' ...

Great sites Nereid!



Very interesting!
 
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  • #11
COOL, thank you all! My whole view of galaxies has been reconfigured!
 
  • #12
Originally posted by Slag
COOL, thank you all! My whole view of galaxies has been reconfigured!
Now all we need to do is introduce you to LSB (low surface brightness) galaxies, galaxies in collision (or merger), ellipticals and lenticulars, even galaxies with more than one supermassive black holes at their core! :wink:
 
  • #13
Originally posted by avemt1
The main theory is that we are spiraling tward the center of the universe.
Gravity itself causes acceleration.

Of course, the main cosmological theory is that there is no center of the universe, at least not in 3D space. So perhaps you meant "galaxy".
 
  • #14
sry i did mean galaxy

In the Big Bang Theory there is a central origination point correct?
If yes then..
1)There should be a central point for all to originate from.
2)Everything would expand from that point.
Correct?
 
  • #15
avemt1 said:
sry i did mean galaxy

In the Big Bang Theory there is a central origination point correct?
If yes then..
1)There should be a central point for all to originate from.
2)Everything would expand from that point.
Correct?


Your premise is not correct. At a few microseconds after the initial singularity, the whole universe was a tiny space. The whole universe then expanded to be the universe we see today. No center.
 
  • #16
I think that no matter where you are in the universe, you perceive yourself as being in the center. There are no civilizations claiming to live near the left edge of the universe.
 
  • #17
First, I did not mean an infinutely small center point, but a region that the universe is expanding from.
Tony i don't believe that is what we are talking about, but applying human perseption is a part of science. Keep up the good work.
 
  • #18
avemt1 said:
First, I did not mean an infinutely small center point, but a region that the universe is expanding from.
Tony i don't believe that is what we are talking about, but applying human perseption is a part of science. Keep up the good work.

According to the standard model of cosmology, the universe is expanding everywhere, not "from" any region or point.
 
  • #19
I have never thought of it by those terms. Its a concept that is very easy to grasp. Is the reason for this because we cannot find the remote region that the universe originates from, or because that is the only way we can define infinite expansion?
 
  • #20
It's the way the general relativity math presents the expansion to us, and is confirmed by our observations. Every volume of the universe is experiencing an expansion, in which the rate, which has its own time dependence, is proportional to the size of the volume too. So the space between the galaxies shows a noticible expansion, while the space between my ears doesn't.
 
  • #21
selfAdjoint said:
Your premise is not correct. At a few microseconds after the initial singularity, the whole universe was a tiny space. The whole universe then expanded to be the universe we see today. No center.
There's a mindset that can't avoid confusion when someone says something like this. It helps to compare space with the surface of an expanding sphere, with the "center" being a point in the past of time.
 
  • #22
but according to entropy all points in time exist at once.
 

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