Dark Matter

[David Levy]

History anddescription of the problem

Wikipedia: "In1932, Jan Hendrik Oort was the first to discover that the stars in thearms of a spiral galaxy (the Milky Way in thiscase) moved faster than expected when a mass distribution based upon the visible matter is assumed.

"Although dark matter is the most popular theory to explain the various astronomical observations of galaxies and galaxy clusters, there has been no direct observational evidence of dark matter."

So, how would Newton explain this Rotation curve of a typical spiral galaxy?

 

Newton hadalready gave the answer:Wikipedia: "Object's orbit in the space is mainly influenced by the gravitational pull of nearby objects to him".

Spiral arm is the ultimate answer for the high velocity of a star which is located far away from the galactic nucleus.

 

The Spiral arm acts as a chain of star which is connected to each other by the gravitational power. This maintains the flat & high velocity. In fact, the galactic nucleus of an active galaxy like the

Milky Way contains a mass of millions of suns. This core rotates on its axis and creates a circularmotion for all the stars which are relatively close to it.

 

Thus, rotation of a star near the galactic nucleus causes a higher speed to another star which is a little farther from the nucleus, but is related to his faculties of gravity.

It can be simulatedas series of balls which are connected by elastic cord to each other. In oneside the cord is connected to a spinning axis. Hence, the velocity of the other end of the cord will be directly affected by the rotation of the axis.

 

The balls in this example are the stars and the elastic cord is the gravitational power.

Note that all the stars in an active galaxy which might contain about 400 billion stars revolve a uniform direction.

This is different from the solar system as some of the stars rotates in the opposite to others.

 

Therefore, unlike our solar system where the velocity of each star is affected by only by the distance from the sun, here the velocity is determined by the velocity of the spiral arm.

Hence, there is no need dark matter to explain the phenomenon of the high velocity of the stars which are far away from the galactic nucleus.

 

Conlusion - there might be some dark stars which areneeded to keep the chain gravitational power. But, there is no real need fordark material outside the galaxy or dark energy to maintain this velocity!

Edited May 30, 2012 by David Levy

[swansont]

Are you proposing a new form to the force? "It can be simulated as series of balls which are connected by elastic cord to each other." doesn't sound like Newtonian gravity.

 

Or are you claiming that thousands of scientists have simply done the calculations wrong? Or some third option.

 

(Oh, and can you not right-justify? That's annoying as heck)

[David Levy]

There is no need for a new form of force.

 

It's the old good Newton!!!

 

"It can be simulated as series of balls which are connected by elastic cord to each other." doesn't sound like Newtonian gravity".

In This example each ball is a star. the elastic core between two stars is a Newton gravitetion power!

 

Therefore, the high velocity is an outcome of the spiral arm interaction power.

 

It's quite amazing that "thousands of scientists" didn't find this simple answer....

 

Please transfer this topic to Astronomy and Cosmology.

Edited May 30, 2012 by David Levy

[elfmotat]

First of all, you realize that Newtonian gravity is only a low-velocity weak-field approximation to general relativity, right?

 

The main issue, however, is that you provide absolutely no quantitative resolution to the problem. It's not enough to say in words that you solved something, you need to provide numbers.

[David Levy]

Newton low:

 

 

Wikipedia: Newton's law of universal gravitation states that every point mass in the universe attracts every other point mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. http://en.wikipedia....sal_gravitation

 

Your question:

First of all, you realize that Newtonian gravity is only a low-velocity weak-field approximation to general relativity, right?

Answer:

No, There is no limit for power or velocity.

 

 

Your question:

The main issue, however, is that you provide absolutely no quantitative resolution to the problem. It's not enough to say in words that you solved something, you need to provide numbers.

 

Answer: Yes, we can set the guantitive resolution if we just knew the correct locations of all the stars in the spiral arms.

 

Please be aware that even at a distence of one year light its highly difficult to see a sun... so now think that you need to see a dark star at a distence of 1000 years light...

 

 

One more question - Do we have any absolutely no quantitative resolution - for the current dark matter theory???

Edited May 30, 2012 by David Levy

[SweetScientist]

Newton low:

 

 

Wikipedia: Newton's law of universal gravitation states that every point mass in the universe attracts every other point mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. http://en.wikipedia....sal_gravitation

 

Your question:

First of all, you realize that Newtonian gravity is only a low-velocity weak-field approximation to general relativity, right?

Answer:

No, There is no limit for power or velocity.

 

 

Your question:

The main issue, however, is that you provide absolutely no quantitative resolution to the problem. It's not enough to say in words that you solved something, you need to provide numbers.

 

Answer: Yes, we can set the guantitive resolution if we just knew the correct locations of all the stars in the spiral arms.

 

Please be aware that even at a distence of one year light its highly difficult to see a sun... so now think that you need to see a dark star at a distence of 1000 years light...

 

 

One more question - Do we have any absolutely no quantitative resolution - for the current dark matter theory???

I'm not going to pretend I'm an expert because I'm not but...

 

Newtonian gravity works for the most part in everyday life and macroscopic ideas and even larger ideas. However it is not totally accurate, proven by the error in the predicted orbits for the planet Mercury. Said error was eliminated with the introduction of general relativity.

 

Newtonian gravity makes complete sense and in our lives is a great model to work things on, however it needed some adjustments to make it fully accurate. It gets even less reliable when you go into the details of faster and more powerful objects as was iterated by elfmotat.

 

 

 

 

[Janus]

Newton low:

 

 

Wikipedia: Newton's law of universal gravitation states that every point mass in the universe attracts every other point mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. http://en.wikipedia....sal_gravitation

 

 

And This is exactly why your idea falls apart.

 

Let's take a closer look why:

The nearest star to the Sun, Alpha Centauri at 4.3 ly. So this is the individual star that would have the strongest gravitational effect on the Sun

 

Now the Sun is ~2/3 of the way,about 27,000 ly, out from the Galactic center. Using your own estimate, there are 400 billion stars in the Galaxy. If we are conservative, we will say that 40% or 160 billion of them are closer to the center than the Sun is.

 

Now it turns out, that if you add up all the individual gravitational gravitational attractions to the Sun of all those stars closer to the Center, The net effect is the same as if they were all bunched together at the center of the Galaxy.(Another thing Newton taught us). Thus is is the same as having the mass of 160 billion stars located 27,000 ly away. This is 6279 times the distance to Alpha Centauri.

 

If we want to compare the relative gravitational pull of Alpha Centauri compared to all these other stars, we 160 billion and divide it by 6279² (39426717)

 

this gives us 4058. This means that the net gravitational effect from these stars is 4058 times more than the gravitational effect of the nearest star.

 

So here's the point: It is this net pull of all these stars that should hold the Sun in its orbit around the galaxy. The thing is that this isn't enough by quite a bit to hold the Sun in its orbit for the speed its moving. Adding the tiny bit represented by the pull of Alpha Centauri wouldn't make a bit of difference.

 

But here's the kicker to even add Alpha Centauri's gravity, it would have to be closer to the center than the Sun, in which case, its gravity is already included in the total pull we've already calculated . So we can't add it again.

 

The simple fact is the Scientists already know how to add together the effect of all the individual stars and the galaxy as a whole, and when they do, there just isn't enough "visible" matter to hold it together by a very large factor.

 

You have not come up with an explanation that does away with dark matter, partly because the effect you rely on ( the mutual attraction between close stars) is just way too weak to have any real effect on the rotational speeds of those stars.

[Bill Angel]

Janus's analysis as to why the amount of visible matter falls short of the amount of matter needed to constrain the sun in its galactic orbit certainly seems reasonable to me, but I would suggest an alternative possibility. If the analysis that determines that the gravitational pull of 160 billion stars located at the galactic center was insufficient to hold the earth in its orbit (without the existance of dark matter), then what would be the effect of incorporating the gravitational pull of the black hole located at the galactic center into the result? How much gravitational pull would that black hole contribute, as compared to this theorized dark matter. And if this dark matter does exist, would not the black hole be sucking it in as well as sucking in ordinary matter? And if so, isn't 80% of the purported mass of this black hole attributable to its dark matter component, rather than to ordinary matter ?

[doG]

If the analysis that determines that the gravitational pull of 160 billion stars located at the galactic center was insufficient to hold the earth in its orbit (without the existance of dark matter)....

Huh? Why do you think the Earth's orbit relies on the gravity of any other stars that it's own?

[ACG52]

How much gravitational pull would that black hole contribute, as compared to this theorized dark matter

 

Not really much at all. Although the BH at the center is estimated to have a mass of 3 million solar masses, that's not much at all compared with the 400 billion in the galaxy as a whole. And gravitation falls off as the square of the distance.

 

The dark matter is theorized to exist in something of a halo surrounding and penetrating the galaxy.

[Janus]

Janus's analysis as to why the amount of visible matter falls short of the amount of matter needed to constrain the sun in its galactic orbit certainly seems reasonable to me, but I would suggest an alternative possibility. If the analysis that determines that the gravitational pull of 160 billion stars located at the galactic center was insufficient to hold the earth in its orbit (without the existance of dark matter), then what would be the effect of incorporating the gravitational pull of the black hole located at the galactic center into the result? How much gravitational pull would that black hole contribute, as compared to this theorized dark matter. And if this dark matter does exist, would not the black hole be sucking it in as well as sucking in ordinary matter? And if so, isn't 80% of the purported mass of this black hole attributable to its dark matter component, rather than to ordinary matter ?

 

 

The BH only masses about 4 million solar masses. We know this by the periods of stars that orbit closely around it. But even if we to assume that it was massive enough to account for the Sun's orbital speed, it wouldn't account for the flatness of the rotation curve. If all that mass were concentrated at the center, the orbital speeds of the stars would pretty much drop of by the inverse of the squareroot of their distance from the center. What we see instead is that the orbital speeds remain close to the same as you move out. This means that the extra mass must be more or less evenly distributed. (so that as you move further away, the amount of mass you are orbiting increases.)

 

Black holes can capture dark matter, it is just not as easily a "normal" matter. As normal matter circles a BH, it collides with other matter causing it to radiate away some of its energy, causing it to fall in closer. DM doesn't react with itself or other matter this way. So it holds on to all of its original energy.

 

The other factor is that while 80% of the Galaxy's mass is DM, is spread out into a much larger volume than the visible disk of the galaxy. Imagine the galactic disk as being imbedded in a spherical "ball" of DM that is much larger than it is. This much larger volume means that, in any given part of the visible disk, the density of DM is much less than visible matter (This also explains why 80% of the Solar system isn't made of DM).

[David Levy]

Answer to Janus

 

 

And This is exactly why your idea falls apart.

Let's take a closer look why:

The nearest star to the Sun, Alpha Centauri at 4.3 ly. So this is the individual star that would have the strongest gravitational effect on the Sun

Now the Sun is ~2/3 of the way,about 27,000 ly, out from the Galactic center. Using your own estimate, there are 400 billion stars in the Galaxy. If we are conservative, we will say that 40% or 160 billion of them are closer to the center than the Sun is.

 

No, the calculation should be as follow:

 

 

Most of the 400,000,000 stars are located at the spiral arms.

Let's say about 70,000,000 stars per arm.

The length of each arm is about 50,000 years light.

 

So there are more than 1000 stars per year light.

That should be good enough to hold the gravitational chain power!!!

 

Hence, the following statment is incorrect:

The nearest star to the Sun, Alpha Centauri at 4.3 ly. So this is the individualstar that would have the strongest gravitational effect on the Sun

 

 

There must be several stars which are much closer to the sun than the Alpha Centauri.

We just need to find them...

Please be aware that not all the stars are simmilar to the sun.

Some of them might be a dark stars. therefore, it is quite difficult to find them.

 

But they are there. One day (hopefully in our life time..) we will find them all....

Edited May 31, 2012 by David Levy

[ACG52]

That should be good enogh to hold the gravitational chain power!!!

 

 

There is no such thing as gravitational chain.

 

Hence, your following statment is incorrect:

 

Thenearest star to the Sun, Alpha Centauri at 4.3 ly. So this is the individualstar that would have the strongest gravitational effect on the Sun

 

 

Therefore; There must several stars which are much closer to the sun than the Alpha Centauri.

 

 

Again, totally incorrect.

 

Education in astronomy would help you.

[doG]

Some of them might be a dark stars. therefore, it is quite difficult to find them.

 

But they are there. One day (hopefully in our life time..) we will find them all....

You need to support this assertion on the existence of dark stars. Evidence please?

[David Levy]

To ACG52

 

 

Did you see the following statement:

 

"Although dark matter is the most popular theory to explain the various astronomical observations of galaxies and galaxy clusters, there has been no direct observational evidence of dark matter."

 

 

Why do you prefer this theory which has --- no direct observational evidence.

 

Is it just because of "thousands of scientists" think so??? Good for you...

 

 

How come that so far no one had found this dark matter???

 

They will never find as it is not there...

 

It's much easier to find the dark stars which should be much closer to the solar system...

 

One day you will appriciate this valuabale info...

[ACG52]

Why do you prefer this theory which has --- no direct observational evidence.

 

Is it just because of "thousands of scientists" think so??? Good for you...

 

 

 

I prefer this theory because there isn't any other which adequately and parsimoniously explains our observations of galactic structure, and this one does.

 

Since dark matter (as theorised) does not interact with the electromagnetic spectrum, and that is our only way of making observations, it has not been 'seen'. We do have indirect observational evidence of the existence of dark matter in gravitational lensing observations.

 

Are you one of these who believes actual knowledge gets in the way of your thinking?

[David Levy]

TAGC52

 

 

I'm not going to argue with you.

 

The dark matter is a pure theory.

 

If you see a man' shadow it does not mean that you see a real man...

 

The dark matter theory is some sort of faith.

 

As I said: good for you...

 

I'm quite sure that we have the technology to find those dark stars.

 

 

Houston,we have a problem!!!

 

We need a help to find those dark stars...

[ACG52]

TAGC52

 

 

I'm not going to argue with you.

 

The dark matter is a pure theory.

 

If you see a man' shadow it does not mean that you see a real man...

 

The dark matter theory is some sort of faith.

 

As I said: good for you...

 

I'm quite sure that we have the technology to find those dark stars.

 

 

Houston,we have a problem!!!

 

We need a help to find those dark stars...

 

Well, there is clearly no T in my name.

 

Everything you've posted on this forum has been inane, illogical, and totally lacking in any kind of fact.

 

You are one of those scientifically illiterate people who believe that their ideas are as good as those who actually know something about the subject.

 

They are known as cranks.

[David Levy]

If this is the best of what you can say...

 

Than, you need to reconsider what you say...

Edited May 31, 2012 by David Levy

[ACG52]

If this is the best of you can say...

 

Than you need to reconsider what you say...

 

You're right..................

 

I've reconsidered. No change.

[David Levy]

Thanks.

 

Do appriciate your support.

 

What a wonderfull world we have...

Edited May 31, 2012 by David Levy

[Bill Angel]

Huh? Why do you think the Earth's orbit relies on the gravity of any other stars that it's own?

That was a mis-statement on my part. What I meant to say was about the orbit of the SUN about the galactic center. I did not intend to make an assertion about the orbit of the Earth about the sun.

[swansont]

There is no need for a new form of force.

 

It's the old good Newton!!!

 

"It can be simulated as series of balls which are connected by elastic cord to each other." doesn't sound like Newtonian gravity".

In This example each ball is a star. the elastic core between two stars is a Newton gravitetion power!

 

Well, no, because if it were Newtonian gravity each ball would be attracted to every other ball. A nearest-neighbor interaction is not consistent with that.

[David Levy]

Yes it is!!!

 

Please reverify the following statment from Wikipedia about newton low:

"Object's orbit in the space is mainly influenced by the gravitational pull of nearby objects to him".

 

So each ball is attracted to the nearest ball. And that one is attracted to the other one... and so on.

A chain of balls under a gravity power.

 

In the solar system there is a minor example:

 

The moon is attracted to the earth.

The earth is attracted to the sun.

 

The sun is attracted to a *** star which will be hopefully find soon...

Edited May 31, 2012 by David Levy

[mississippichem]

Let's see your calculation OP.