Does gravity act differently on a Solar System, a Galasy, and the Universe?

In summary, according to Newton's law, gravity decreases as the inverse of distance, making it weaker at large distances. This explains why our Sun was unable to pull in matter from the Oort cloud for over 4 billion years. However, at a distance of about 0.11 light years, modified Newtonian dynamics equations show that gravity decreases by the inverse of distance only, resulting in a slower decrease. On a galactic scale, dark matter may not be necessary to explain certain phenomena, but it is needed to explain the formation of stars in the early universe. While modified Newtonian dynamics is a potential solution for galaxy rotation curves, there are also observations that do not adhere to this theory. As we continue to study and discover more
  • #1
KurtLudwig
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TL;DR Summary
Newton's law predicts gravity for our solar system almost perfectly. On a galactic scale, modified Newtonian dynamic equations predict the stellar rotation curves. On the scale of our Universe, black matter is needed to explain large scale phenomenon.
Since acceleration due to Newton's law decreases as the inverse of distance, it becomes very weak at large distances. Our Sun was unable to pull in matter in the Oort cloud in over 4 billion years. Above about 0.11 light years, using modified Newtonian dynamics equations, gravity decreases by the inverse of distance only. Gravity at that distance from the sun is about 1.2 x 10^-10 m/s^2. That is, gravity decreases much more slowly. On a galactic scale, there is no need to assume dark matter. However, to explain formation of stars in the beginning of our Universe, gravitational wells of dark matter were needed. Other very large scale phenomenon can be best explained by existence of dark matter.
 
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Is there a question here?
 
  • #3
KurtLudwig said:
modified Newtonian dynamic equations predict the stellar rotation curves.
Not so much. Recent observations have detected galaxies that have rotation curves that are close what Newtonian Physics predicts, while other very similar galaxies have rotation curves that differ significantly from the Newtonian norm. If MOND was the sole answer to galaxy rotation curves, it would have to be consistent from galaxy to galaxy; similar galaxies would have to have similar rotation curves. The newly discovered galaxies don't adhere to this pattern.
 
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  • #4
MOND is a contender, but seems to pose more questions than answers, and doesn't seem to apply evenly. For every example of galaxy or galaxy group that 'needs' MOND, there seems a counter example that doesn't. Plus a couple 'in between'.

Like 'Dark Matter', or loathe it, there's wide gaps in our census of galactic stuff. How common are 'Intermediate Mass Black Holes' ? Finding a significant population of them would fix one big gap. Finding a lot more 'sub-Brown Dwarf' L/T/Y types in our solar neighbourhood would shift the 'mass function'. Assuming, if we dare, that our location within an 'interstellar bubble' is even mildly representative of wider 'Spiral Arm'...
https://en.wikipedia.org/wiki/Local_Bubble

So, beyond the usual astro-sites, I keep a wary eye on RECONS: (REsearch Consortium On Nearby Stars) "...To understand the nature of the Sun's nearest stellar neighbors, both individually and as a population. Our primary goals are to discover "missing" members of the stellar sample within 10 parsecs (32.6 light years), and to characterize all stars and their environments within that distance limit. "
http://www.recons.org/
 
  • #5
The question was implied: Can both dark matter and modified Newtonian dynamics help us explain the clumping of matter, gravitational lensing and galaxy rotation curves. Does it have to be either or? Can it be both? Phenomenon of light are explained by waves and particles.
The ideal gas laws, which need to be sometimes modified due to Van der Waals forces between molecules of some gases. Maybe astronomers are missing a gravitation phenomenon between stars?
I do defer to Janus' knowledge on astronomy. Please take this post as questions. I find astronomy very interesting and am amazed at the insights discovered during the last twenty years and during the last century.
 

Related to Does gravity act differently on a Solar System, a Galasy, and the Universe?

1. How does gravity work in a solar system?

In a solar system, gravity is the force that holds the planets in orbit around the sun. The sun's massive gravitational pull keeps the planets in their respective orbits, while the planets' own gravity keeps their moons in orbit around them.

2. Does gravity work differently in a galaxy compared to a solar system?

While the basic principles of gravity remain the same, the strength of gravity can vary depending on the size and mass of the objects involved. In a galaxy, the gravitational pull of the supermassive black hole at its center can influence the motion of stars and other objects within the galaxy.

3. How does gravity behave in the universe?

In the universe, gravity is the force that governs the motion of all objects, from planets and stars to galaxies and clusters of galaxies. It is responsible for the formation and evolution of structures in the universe, such as galaxies and galaxy clusters.

4. Can gravity be stronger or weaker in different parts of the universe?

Yes, the strength of gravity can vary in different parts of the universe. This is due to the distribution of mass and energy in the universe, which can affect the strength of gravitational pull in a particular region.

5. How does gravity affect the expansion of the universe?

Gravity plays a crucial role in the expansion of the universe. It is the force that acts against the expansion, trying to pull matter back together. However, the expansion of the universe is currently accelerating due to the repulsive force of dark energy, which is stronger than the attractive force of gravity at large scales.

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