Dark Matter

[Bill Angel]

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).

 

Still, some issues about the characteristics of Dark Matter come to mind. The idea that the galactic disk is imbedded in a spherical "ball" of DM that is much larger than the disk itself would suggest that near the beginnings of the universe ordinary matter and dark matter were uniformly distributed, and in the region of space containing our galaxy the ordinary matter coalesced into our spiral galaxy, while the dark matter associated with this region of space did not. One can also imagine a simply physics experiment. Suppose one suspended at the ends of two strings a ball of ordinary matter, and a ball of dark matter. Now it is postulated that the two balls will attract each other gravitationally. Assuming that the balls are of equal mass, would the ordinary ball move slightly towards the dark matter ball, while the dark matter ball remained motionless in space? Wouldn't one expect the equal forces on each of the balls to cause them to move equally towards each other?

[ukgazzer]

i/ If acceleration due to gravity is due to the sum of the contributions of all masses, how can this acceleration provide us with a figure for the actual amount of mass present? For example (an extreme case!) if we were living in the centre of the Earth,we would feel weightless. To me it seems that orbital motion only reveals the difference in gravitational attraction from opposite directions. How does orbital motion provide a reliable way to determine the actual masses or mass distribution?

ii/ Is there a formula for the relationship between the number and size of bodies in the universe? How many different processes are at work to determine how frequently things get big? If there is a formula,what does it suggest for the number of brown dwarfs etc in the galaxy? How much do they contribute to the missing mass?

iii/ How reliable is the principle that material will produce a gravitational field directly proportional to its mass? I`m only aware of an established and reliable relationship with cosmically very small masses. Why do we get stuff orbiting/GOING AROUND BHs in spiral patterns in the 1st place if there`s no connection between the BH and the pattern?

[Janus]

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...

 

That statement from Wikipedia is a Generalization which is not always true.

 

For example, the Moon is closer to the Earth than the Sun is, yet the Sun exerts a greater influence on the Earth than the Moon does. In matter of fact, the Sun also exerts a greater influence on the Moon than the Earth does in terms of the Moon's path around the Sun.

 

The Sun may be 400 times further away, but it is also 330,000 times more massive. 330,000/400^2 = ~2, meaning that Sun exerts twice the gravitational pull on the Moon than the Earth does.

 

As far as your claim that there are nearby(closer than Alpha Centauri) stars that we've yet to discover, that is laughable. We can presently detect a star 1/100 the mass of the Sun that is 40 ly away. To suggest that that there are stars closer than 4.3 ly that we haven't found is just silly.

 

Still, some issues about the characteristics of Dark Matter come to mind. The idea that the galactic disk is imbedded in a spherical "ball" of DM that is much larger than the disk itself would suggest that near the beginnings of the universe ordinary matter and dark matter were uniformly distributed, and in the region of space containing our galaxy the ordinary matter coalesced into our spiral galaxy, while the dark matter associated with this region of space did not. One can also imagine a simply physics experiment. Suppose one suspended at the ends of two strings a ball of ordinary matter, and a ball of dark matter. Now it is postulated that the two balls will attract each other gravitationally. Assuming that the balls are of equal mass, would the ordinary ball move slightly towards the dark matter ball, while the dark matter ball remained motionless in space? Wouldn't one expect the equal forces on each of the balls to cause them to move equally towards each other?

 

"ordinary" matter bunches up much easier than DM for the very reason that DM is "Dark". If you have a number of normal matter particles milling around they will bump into each other, doing so creates "heat" which is radiatied away. this leaves the matter with less kinetic energy which make it more subject to gravitational collapse. Closer bunching causes more collisions leading to more heat loss, leading to tighter bunching, etc.

 

DM On the other hand does not interact electromagnetically. It does not collide with itself or other matter. Neither can it emit electromagnetic radiation in order to bleed away energy. It only interacts gravitationally. Close encounter with other matter can cause it lose energy via gravitational radiation, but gravity waves are much much less energetic than electromagnetic wave, so the process of forming "clumps" it much much slower. Thus it has only had enough time to collapse into the much looser Dm halo, while the visible matter has collapsed to the smaller disk.

[Bill Angel]

There is an interesting article in the May 31, 2012 issue of ScienceDaily titled "Clash of the Titans: Milky Way is Destined for Head-On Collision With Andromeda Galaxy". So here is a speculation: galactic collisions are a well studied occurance in the observable universe. Might it be possible to confirm the existence of dark matter by observing how these collisions play out? Cosmologists model how these galactic collisions evolve. Would the models improve if "dark matter" is included in the calculations? If two galaxies are each surrounded by spherically shaped concentrations of dark matter, how might each of these spherical distributions be distorted as the two galaxies approach each other and then merge?

[Janus]

There is an interesting article in the May 31, 2012 issue of ScienceDaily titled "Clash of the Titans: Milky Way is Destined for Head-On Collision With Andromeda Galaxy". So here is a speculation: galactic collisions are a well studied occurance in the observable universe. Might it be possible to confirm the existence of dark matter by observing how these collisions play out? Cosmologists model how these galactic collisions evolve. Would the models improve if "dark matter" is included in the calculations? If two galaxies are each surrounded by spherically shaped concentrations of dark matter, how might each of these spherical distributions be distorted as the two galaxies approach each other and then merge?

 

We already have an example like that, it is called the Bullet Cluster. It is the collision between two galaxy clusters. Remember what I said about what happens when normal matter collides? It radiates heat and loses kinetic energy. So what happens with the Bullet Cluster is that the visible matter is slowed down a bit after the collision. The dark matter doesn't however and retains its speed. It is, in essence, "knocked loose" from its parent cluster

 

We can map DM by looking for its "gravity shadow". Its mass causes gravity lensing and distortion of the light passing through and around it. So when we look at the Bullet cluster, we would expect to see a gravity shadow that is offset from the visible mass. (you should see two gravity shadows, one for the visible cluster, and one for the DM that has been knocked loose.)

 

This is, in fact, exactly what we see. One gravity shadow surrounding the visible matter and a second one offset from that with no associated visible matter.

 

The Bullet cluster is the closest thing we've seen to being direct evidence of DM, and is a nail in the coffin of purely modified gravity alternatives. (That's not to say that a modified theory of gravity is completely off the table, but that any such theory would have to include some type of dark matter.)

[swansont]

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".

emphasis added

 

You have changed this to "exclusively" with your model.

[warped space]

Not to argue on weather or not dark matter exists but is there a possibility that other galexys and etc basically im saying this newtonian gravity of the other galexys and stars and also not to mention other planets orbiting stars