What evidence is there for dark matter in the Milky Way Galaxy?

Question

What evidence is there for dark matter in the Milky Way Galaxy?

Answer 1

My problem with this is the dependence on a supermassive black hole at the center.  And I do not believe they saw evidence that required the existence of vast amounts of dark matter.  They *wanted* a much greater amount of mass because that would "close" the universe and immortalize the person who proved it.  So the *need* for dark matter came first.

Now what about the super-massive black hole (SMBH)?  They have proposed masses as much as 10^10 solar masses, (ten billion).  If such a mass existed, the orbits of stars near the center would be MUCH faster than we observe.  So instead of considering that the mass at the center isn't nearly that big, they invent *other* mass outside of it, which would account for the orbits being as slow as they are.  The amount of mass you have to invent, being widely dispersed through the galaxy, would have to be many times greater than the mass of the SMBH in order to have this dampening effect.  When you get out as far as the solar system, we should be going much faster, too, because of the huge increases in estimated mass between us and the center.  Serendipity again!  This means that the "dark" matter must extend well past the visible edges of the galaxy and be many *more* times greater.

Every billion solar masses they add to the SMBH results in about 100 times more dark matter necessary to yield the observed rotational rates.  So it looks to me like they are inventing one thing to prove the existence of something else.  There might be more matter that we haven't accounted for, but I'm talking about ordinary, baryonic matter, and that can't come close to making the mass of the universe great enough to stop its expansion and possibly end in a Big Crunch.  Dark matter is supposedly non-baryonic.  Yes, it has the lovely characteristic of being completely invisible and non-reactive with ordinary matter.  All we can "see" of it is its gravitational effect.  And yet, they say it might constitute 90% of the mass of our galaxy and the universe.  It's still not enough to close the universe, so I gues they'll have to just keep coming up with bigger and bigger SMBH's.

I don't buy it.

Ohhhh, despair.  I'll never make any friends this way.

Answer 2

Dark matter was invented to prevent the galaxy from flying apart.

  The outer arms of the galaxy are locked in step with the galactic center,if the galaxy was a satellite system it would require dark matter to prevent it from flying apart.

  The galaxy may be driven by some other force than gravity,in which case dark matter wouldn't be needed.

Answer 3

Astronomers have hypothesized that the amount of visible matter (e.g. stars, gas and all that stuff that can be seen) in the galaxy is not enough to hold the entire Milky Way together via gravity. Assuming that the amount of matter in the Milky Way Galaxy = the amount of visible matter, then the Milky Way Galaxy would be dispersing.

But that's not the case. Therefore, there is a large amount of unseen matter that is holding the galaxy together. That's dark matter.

Answer 4

There is insufficient visible matter in our galaxy to produce the observed gravitational effects, only about 10% of what ought to be visible. The same is true of many other galaxies. This is what led astronomers to believe that there must be some other, invisible form of matter in our galaxy, exerting its own gravitation.

Answer 5

the simplest evidience is the motion of sun. the sun is rotating around milky way at around 220 km/sec. and acc to kepler's calculations it should rotate at 160 km/sec.