Why do you call dark matter dark?

Answer 1

"Dark" in the phrase "dark matter" comes from the fact that it interacts with ordinary matter only very weakly (at most) except through the gravitational force (and, for certain possible types of "dark matter" since we're not really sure what it is exactly, through the weak force, but that's strictly limited in range).

Since it does not interact through the electromagnetic force, and photons (light) are the gauge particles for the electromagnetic force, "dark matter" seems like a pretty reasonable name.

Don't confuse "dark" with "black": in order to be black, something has to absorb photons. Dark matter neither absorbs nor emits photons. This also means you can't feel it, since the apparent solidity of matter is also a function of the electromagnetic force. It is literally invisible and intangible.

Answer 2

SURROUND the galaxy? There's no particular evidence of that.

WITHIN the galaxy? We know that there must be far more mass in the Milky Way galaxy than we can see directly, because the Milky Way seems to be spinning faster than it ought to. With only the mass that we can SEE, we think the Milky Way ought to disintegrate, with stars flying off into the Void in all directions.

So astronomers think that there must be "invisible" mass. Some astronomers suspect that there is a supermassive black hole at the center of our galaxy - or that there are such supermassive black holes at the centers of MOST galaxies. In fact, some astronomers theorize that the quasi-stellar objects - "quasars" - that shine so brightly, so far away, might be the blaze of those black holes being formed. Quasars are a very long distance away - so we're seeing light from very long ago. It's like looking back in time! Was our Milky Way once a quasar itself? We don't know.

Other scientists believe that even a supermassive black hole at the galactic center wouldn't provide enough gravity to hold the Milky Way together, so they postulate a "dark matter"; some mysterious sort of gravity-producing mass that isn't like the mass that we can see.

But if there is "dark matter" within the galaxy, why SHOULDN'T it surround the galaxy? Perhaps it does!

Answer 3

The known mass is way too low to account for the fast rotation of the galaxy.

The known mass is way too low to account for the fast rotation of the galaxy.

The known mass is way too low to account for the fast rotation of the galaxy.

The known mass is way too low to account for the fast rotation of the galaxy.

Answer 4

When we look at our Universe, we observe things that can NOT be explained by assuming that luminous matter comprises a large part of the mass of our Universe. These observations can ONLY be explained by assuming that something we don't fully understand interacts with baryons via gravity but not in any other way. Two of these observations agree, independently of each other, about the amount of this mass in our Universe.

We are presently at the state that Johannes Kepler was in -- he knew that planets DID move around our Sun in ellipses, he just couldn't explain WHY.

Answer 5

Calculations and computer simulations were done in regards to The Big Bang Theory. It was discovered that the universe would have a density of 1 if the Big Bang is, in fact, true (the density of the universe is known as the omega value). When the time came to measure the actual density and compare it to the theory, scientists came up with a value of .2 (80% less matter than would be expected). This experiment was performed numerous times, each with a value of .2.

At that point, there are only two possibilities. They could either admit that the Big Bang never actually happened, or they could say that they are somehow not accounting for 80% of the matter in the universe. Rather than scrap the Big Bang, it was concluded that 80% of the universe is stuff that we cannot see. That brings the omega value back to one and keeps the Big Bang alive.

As far as evidence goes, it is really scant. The scientists try to argue that the gravitational effects of dark matter can be observed, but there are a lot of alternative and better explanations for many of those effects.

In essence, dark matter was "made up" to bring the omega value up to 1. And astronomers must believe that it exists, because if it does not than they have to get rid of the precious Big Bang theory.

Answer 6

Both dark matter and dark energy are "dark" because they give off no visible light. Think of it... The universe is filled with literally trillions of stars, all giving off tremendous loads of light. Why is it that the night sky isn't always bright? There is something interfering with the light, such as a dust storm would make day like night. That matter that interferes with all of the light from billions of stars and keeps it getting to where we are is referred to as "dark matter".

As for dark energy, it gives of no visible light. A neutron star is theorized as giving off the bulk of its energy outside of the visible spectrum. Even our own Sun emits most of its energy invisibly.

Answer 7

Dark matter cannot be seen directly detected; i.e. it neither emits nor absorbs light or other electromagnetic radiation at any significant level. Instead, its existence and properties are inferred from its gravitational effects on visible matter, radiation, and the large-scale structure of the universe.

Answer 8

The Milky Way (as well as other galaxies) rotates way too fast for the amount of known matter.

Answer2: Dark matter is suggested because most astronomers seem constrained to view the galaxies rotation as caused by gravity. An alternative explanation for the fast rotation is electromagnetism. Electricity is the major factor in the Universe and is likely the cause of the fast rotation. The energy for the fast rotation is the vector energy, Ev=mcV. This energy is the vector energy that is missing in physics theory. This is the same vector energy that explains "Dark Energy". This is the real Cosmological Constant, except it is not a constant.

The short answer for the fast rotation is the galaxies rotate like the homopolar motor used in most homes power meter. As electric current comes into the motor/galaxy the faster the motor turns. This was postulated by Hannes Alfven in 1986.

The math is the same as a mass spectrometer:

mv2/r = qVxB =qvBsin(x)

v=erBsin(x)/m = euIsin(x)/m = ezIsin(x)/mc thus mcv = ezIsin(x).

The Galaxies rotate fast as a result of the electrons entering the galaxy and crossing with the current created by the moving charged stars. The rotating charged stars create the B field in the Galaxy. This same effect causes the sun to rotate at the equator tham at higher lattitudes.

Answer 9

The Milky Way rotates way too fast for the amount of known matter, so there must be some matter of unknown composition - the so-called "dark matter".

Answer 10

Because we can't see them. We can only see the effect of them.