Newton's Second Law of Dynamics

[Grandpa]

According to Newton's inverse-square law for gravitation, the speed at which an object orbits the center would decrease inversely with the square root of the orbital radius.

It's true enough for the planetary orbits around the sun.
It can be seen that the average orbital speed of a planet at a specified distance away from the sun decreases inversely with the square root of the radius of the orbit.
Pardon my crude drawing...


The Galaxy (our Milky Way Galaxy) contains about 300 billion stars and has a total mass of about a trillion times the mass of the sun.
It is called a "Barred Spiral Galaxy" meaning that it is spiral shaped with bar of bright stars emerging from the center and spaced across the middle of the galaxy.

If our understanding of Physics is true and Newton's second law about gravity, velocity and distance holds true and applies, the stars at the outer parts of The Galaxy would rotate around the center at a much slower rate than those located closer to the center.
Velocity as a Function of Distance predicts this.
Newtonian Physics demands this.

Question: How come the stars at the outside of the galaxy rotate at the same rate?
Question 2: How come even small objects on the outside rotate at the same rate?

If you research the question, fine. Please quote your sources.

~Granps

[crazyskwrls]

1. are u sure the starts in the middle of the galaxy rotate the same speed?

2. same as above...

my theory, may be terribly wrong cuz i havent taken physics yet

in the middle its a giant black hole, so newton's theory does not apply there

[Grandpa]

1. are u sure the stars in the middle of the galaxy rotate the same speed?
Answer: YES.
2. same as above...
Answer #2: Same as above...
my theory, may be terribly wrong cuz i havent taken physics yet

in the middle its a giant black hole, so newton's theory does not apply there

The answer to your questions is twofold: Yes I am sure and yes scientists are also sure.

Your theory about black holes in the center of the galaxies is commonly held to be true as well. But that is why the velocities should change and that is why Sir Isaac Newton's LAWS (not theories) should apply. I don't want to give the answers here, thought I'd fish for people who liked astrophysics first.

[boast]

aren't we still answering this, as we learn and discover more about "dark energy" and "dark matter"

(and i assume there are other theories as well)

[/Pi]

I remember watching something about the Dark Matter as the solution to this problem. It sounds interesting, but isn't this concept highly speculative? I'm not really good in math, nor in physics (haven't even taken high school physics before) but observing Dark Matter in nature is almost impossible - close to the String "Theory".

[Grandpa]

The "concept" of Dark Matter and the later proposed "Dark Energy".

That's is the most accepted theory, yes. There are skeptics though. Some propose that gravity is stronger in some places than others. Nobody likes going up against Sir Isaac Newton but they are searching for a way to explain what they observe.

"Dark Matter" is strange stuff indeed, but looking for it may even be stranger. This stuff isn't made out of atoms. It has mass. It doesn't have electrical charge. It isn't "anti-matter". They've been "looking" for it - actually testing things we actually can detect to find any effect - for more than 16 years now. No luck.

More problems come along too - because we are "missing parts of the universe". I really like the way they use language and I know they are smart and all but scientists (especially cosmologists) are looking for stuff that can not be seen (Dark Matter) and stuff that can not be understood (Dark Energy).

I am very much interested as we approach 2009, the "Year of Astronomy" and expect even more information to be released.

~Granps

[boast]

I remember watching something about the Dark Matter as the solution to this problem. It sounds interesting, but isn't this concept highly speculative? I'm not really good in math, nor in physics (haven't even taken high school physics before) but observing Dark Matter in nature is almost impossible - close to the String "Theory".

Dark matter is just the name for "numbers that makes our calculations work". They were simulating computer models, but they would fail after one cycle. They found that putting more matter fixed it, but this matter did not exist in space. So they called it "dark matter." Then came about dark energy for explaining things like the expanding universe and such.

But it's all the rage these days. Does CERN have upcoming any experiments and projects that deal with dark stuff?

[Grandpa]

CERN? Particle Accelerators?
Well, I don't know of any specific studies but they are closely linked to Big Bang theorists as you have implied.

There are a couple unexplained problems and there are many research projects going on. To my amateurish way of thinking it all stems from our measuring speeds at great distances. Comparing Brightness and "Doppler" Red-Shift are the two main methods. I personally can't imagine the proper perspective for distances. Our closest stellar neighbor is Proxima Centauri, 4.22 light years away. The Milky Way is 100,000 light years wide with a thickness of 1000 light years. There are literally billions of galaxies in the known universe.

Okay, how big is a billion???
You were 87,840 seconds old exactly 24 hours after the moment you were born.
When you reached 1 million seconds, you were less than 12 days old.
How old were you when you reached a billion seconds?
It takes a little over 32 YEARS to reach a billion.
Big difference between a million (12 days) and a billion (32 years) .
When we start talking about things that are 100,000 LIGHT YEARS wide and then say there are BILLIONS of them and say that the space in between the galaxies is bigger still... well, you get the idea.

Observers wanted to find out if there was enough matter in the universe to reverse the outward motion. All matter is moving away from us at startling speeds and this fact supports the theory known as Big Bang. They wondered if the universe was only getting slower or if there would be a chance of it halting and then contracting and shrinking back.

BIG SURPRISE: The outward motion of the universe is accelerating. There is no known scientific reason for it, hence "dark energy". We gotta blame something, right? According to the math and recent studies only 4% of the universe is comprised of baryonic matter. Baryons are the stuff that make up atoms. So 96% of the universe is comprised of 'other stuff'.

CERN and particle accelerators come in because that's how we study quarks and sub-atomic particles (baryonic matter). It is surmised that the collisions and energy that results from these collisions most closely represent the universe at the time of the Bang. Well, maybe 1/10,000 of a second after, that is.

Click to enlarge: