What evidence do astronomers have for the existence of dark matter?

Answer 1

1) The measured velocities of stars in the outer reaches of galaxies.

2) The distortion of the path of light from distant galaxies.

Neither of these can be explained by the amount of luminous matter we see in galaxies and in our Universe, meaning either we don't understand gravity OR there's some stuff out there we don't understand. The latter idea is conceptually easier to overcome, but it still leaves open the simple question: what IS that stuff? Because we can't answer that question, we simply call it "dark" matter.

We will, one day, likely understand dark matter as well as we understand x-rays today -- even though the latter were, when first found, so mysterious we called them 'x' rays.

Answer 2

There are 3 major pieces of observational evidence for dark matter.

1) Studies of the dynamics of clusters of galaxies indicate that the individual galaxies within the clusters are moving too fast for the clusters to hold together, based on the amount of visible matter the cluster contains. This indicates that there must be a large amount of non-visible matter, whose gravity helps bind the cluster together.

2) Galaxies do not rotate in the manner that would be expected if the visible mass of stars and gas was all the galaxy contained. Neptune, for example, has a much larger orbit than Earth, but Neptune also moves much more slowly in its orbit because it is much further away from the Sun's gravitational influence. This effect is not seen in galaxies; stars well out from the center move at essentially the same speed as stars that are closer in. This indicates that there must be a large amount of non-visible matter in the outer reaches of the galaxy; its gravitation acts to boost the speed of stars in their orbits.

3) Einstein's theory of general relativity predicted that gravity should bend the path of a beam of light, and, to be sure, it does, and by exactly the amount that GR predicts. This means that gravity from large amounts of matter should act like lenses, in effect, and distort the images of more-distant objects. This effect is easily seen in images of large clusters of galaxies -- the images of galaxies that are well behind the cluster are, in fact, highly distorted. Once again, this distortion is far greater than can be accounted for by the visible matter in the clusters.

Another bit of evidence comes from observations of the Bullet Cluster, consisting of two small groups of galaxies that collided head-on. The aftermath of the collision, which we see now, shows that the normal-matter gas in the clusters collided, canceling their momentum, and left the gas sitting at the site of the collision. The two galaxy groups, however, still retain a large amount of non-visible matter, traveling with the galaxies, that passed right through the collision without slowing down.

A debate has been going on for many years abut whether there is enough dark matter in the universe to eventually slow it's expansion, and begin to draw it back together, culminating in a "Big Crunch" (opposite of the "Big Bang".) The current opinion among physicists is that there is not, and the universe will continue to expand perpetually - but this may change some day with new discoveries and better understanding of the universe.

Answer2:

There is no evidence of "dark Matter". Matter creates a velocity vector field that is proportional to the inverse square of the distance, not independent of distance. Thus the speed profile does not indicate gravitational matter created speed.

Gravity bends light because light has mass, not General Relativity. Finally, Bullet Clusters, if matter in clusters don't don't make impact momentum will be constant and not change passing thru. If 2 shotguns square off with shot, not all buckshot will find a mate.

"Dark Matter" is likely "Dark Energy, cP, vector energy. The galaxies may be operating like Homopolar Motors. The Universe has electricity and electricity entering the galxy drives the motion like a motor.

mv2/r = eVxB = evB

v=e/mBr=(e/m)uI = 176G 1.25u I = 220k I

This a motor action, current enters the edge of the galaxy at 200km/s causing the galactic bodies to move at 200km/s in response to the magnetic field B= uI where i is about 1 amp. The current I results from the motion of charged bodies in the galaxy. The charged bodies rotating creates a current and the current creates the B-field. Gravity is also causing the bodies to rotate but much slower. The incoming current on the edge causes the rotation to be faster and independent of distance.

Most physicists recognize that a current will cause a magnetic field, well the smae effect happens when gravity rotates charged bodies causing a current and this creates a magnetic field. There is no Dark matter here, just plain old electromagnetism in the galaxy.

The Universe has 2E53kg matter and is bounded with radius around 155E24meters. The red shift data is mis-understood. Red shift indicates the " Continuity Condition", the balance of centripetal force vp/r to centrifugal force cp/r cos(P).

Answer 3

Dark matter has been postulated to explain why the stars do not follow Kepler's laws (as the planets do) as they move round the galaxy. Instead they rotate together like a giant catherine wheel, and dark matter can explain it.

Answer 4

Most of the evidence for dark matter is indirect. The big "smoking gun" for dark matter is that galaxies don't appear to rotate as they should assuming that a) we can see all the mass of the galaxy and b) Newton's Law of Universal Gravitation really is "universal".

We can explain the observations in one of two ways:

1. We can assume there's a lot of mass that we can't see (i.e. "dark matter") hovering around near the galaxy

2. We can assume that gravity doesn't work the way we think it does.

Our understanding of gravity must be at least okay, since it lets us shoot spacecraft at planets hundreds of millions of miles away and not miss. So most people have gone with the "dark matter" explanation.

However, some scientists have suggested that it's possible that gravity behaves differently at very large scales. This is not impossible; about a hundred years ago it turned out that a lot of physics didn't behave the way everybody thought it did at the scale of the very small, so it's plausible that physics might behave differently than everybody thinks it does at the scale of the very large, and the Law of Universal Gravitation is really only true on a sort of intermediate scale, which (since we happen to live at that scale) means it works out fine for predicting the orbits of planets and spacecraft within the Solar System, but doesn't work on scales of hundreds of thousands of light-years.

Answer 5

This is the correct answer I got it right in a test for school I took. Here it is The motions indicate a greater gravitational pull from what we see of it