Dark Matter Interactive (150.0K)
Look at telescope pictures of the Milky Way, and you’ll see countless stars, representing enormous mass. But there’s even more mass there that you can’t see! This Interactive will help you understand how astronomers know that. Set up a galaxy with no dark matter, and look at the speeds of the orbiting stars. Then increase the dark matter in steps, plotting the star velocities on the graph after each step. What happens to the velocities? Why? This Interactive will help you figure it out.

1		In which of these galaxies would Newtonian motion (outer stars slowing down father away from nucleus) be best approximated? Need a Hint?
			A)	A spiral with about 50% visible, 50% dark matter.
			B)	An irregular with 10% visible, 90% dark matter.
			C)	An E0 elliptical with almost no gas, dust, or dark matter.
			D)	It does not matter. In all galaxies, the same Newtonain physics applies, and the outer stars must trail behind.

Just as our vision reveals only a tiny portion of the entire electromagnetic spectrum, so bright stars are a tiny fraction of all the forms of matter and energy in the universe. Here we will explore how it is found and arrayed in space.

2		As we added dark matter in every case, what did this do to the speeds of the inner and outer stars? Need a Hint?
			A)	All speeds increased the same.
			B)	The stars near the center slowed down, but outer ones were accelearated.
			C)	All stars sped up, but the outer ones gained the most.
			D)	All were slowed down by the tidal drag of the dark matter.

Our studies of the motions of the outer portions of the Milky Way and most other galaxies reveal that the majority of their mass must be in the form of mysterious dark matter, now detected only by its gravitational influence on the motion of visible objects in the galaxy.

3		In this interactive, what sort of galaxy is used as our example? Need a Hint?
			A)	A normal spiral galaxy.
			B)	A barred spiral galaxy.
			C)	An elliptical of type E 7.
			D)	An irregular galaxy.

When we plot the graph of the vecloty of the stars versus their distance from the center, we get most interesting results. Here we will explore how dark matter is found and arrayed in space.

4		In this interactive, for which of the graphs was the result most curved, and closest to the one we are familiar with for the planet orbits about the Sun? Need a Hint?
			A)	0%
			B)	25%
			C)	50%
			D)	100%

We can apply this interactive not just to stars within a given galaxy, but to galaxies within clusters of galalxies. If indeed the majority of their mass must be in the form of mysterious dark matter, then we will explore how it is found and arrayed in deep space.

5		In clusters, if the majority of mass is dark matter, how would the galaxies behave? Need a Hint?
			A)	The cluster must condense into one huge E 0 galaxy quickly.
			B)	The inner members, close to the central E 0 giant, must move the fastest, just as in our solar system.
			C)	All galaxies in the cluster are moving at the same speed, driven the the 50/50 mix of light and dark matter.
			D)	The outer galaxies are moving so fast it looks like they must escape the cluster, if there is not a huge amount of dark matter present.