A ball of gas reported to be more massive that a billion suns "is hurtling like an enormous comet through the interior of a distant galaxy cluster," writes Ker Than for Space.com. Astronomers believe the immense blob is held together by dark matter and that it was formed during the collision of two star clusters, billions of years ago. Read more here(1).

1. http://space.com/scienceastronomy/060612_gas_comet.html