I'm posting this here because it is so new and is reflective of many of the questions that are floating around right now.
We can't see it, but we can see its effects.
http://news.bbc.co.uk/1/hi/wales/south_east/4288633.stm
Astronomers say they have discovered an object that appears to be an invisible galaxy made almost entirely of dark matter.
The team, led by Cardiff University, claimed it is the first to be detected.
A dark galaxy is an area in the Universe containing a large amount of mass that rotates like a galaxy, but contains no stars.
It was found 50 million light years away using radio telescopes in Cheshire and Puerto Rico.
The unknown material that is thought to hold these dark galaxies together is known as 'dark matter', but scientists still know very little about what that is.