Although dark matter canot be see directly with our naked eyes, its present can be detect because its gravity bends and magnifies the light coming from more distant objects - a phenomenon known as gravitational lensing. By measuring the amount by which the more distant lights has been "lensed" and distorted, the team os astronomers using the Hubble Space Telescope were able to infer how much dark matter were present. they found it was in a ring around the cluster ZwC10024+1652, five billion light years away.
A composition image of the galaxy cluster ZwC10024+1652 with the inferred invisible dark matter added as the blue ring
Image: NASA/ESA/M J Jee and H Ford (John Hopkins University)
Curious about the ring?
Well, the curious ring shape can be explained by the collision between this cluster and another smaller cluster which happened about 2 billion years ago. This is the second example of dark matter being found around galaxy clusters. The first instance was the Bullet Cluster, found in October 2006.
Our Milky Way galaxy also in future, as predicted by astronomers will collide with Andromeda, which located about 2 billion light years from us today. The Andromeda is move toward us, with average speed of 500,000 km/s. And, if its really happend, it will be the end of both galaxy, and soon, a new galaxy will slowly born from the collision.