It often seems as though every few years one astrophysical quantity or another turns out to have a value quite different from what was thought. Now, the entropy of the universe as a whole has joined this list. Chas Egan and Charles Lineweaver of the Australian National University in Canberra have used measurements of the supermassive black hole function to show that these black holes are by far the largest contributors to the entropy of the universe. They find that the monsters supply at least an order of magnitude more than previously estimated. They have also made a first calculation of the entropy associated with dark matter within the universe.
Further reading
Chas A Egan and Charles H Lineweaver 2009 http://arxiv.org/abs/0909.3983.