Francine, the astronomy world is very pleased to see three astronomers get the Nobel Prize for physics. I was at a Royal Society conference on cosmology a number of years ago and Saul Perlmutter (one of the three laureates) was present.
I was still doing my MSc in astronomy then and as I looked around the room, trying not to be too obvious about reading people's name tags, realised that most of my reading list was walking around there!
The current interpretation of what Perlmutter, Schmidt & Co discovered is that it's some sort of energy (dark, because nobody knows what it is!) that is acting in opposition to gravity to speed up the expansion of the universe.
Cosmologists calculate that what we and stars and mundane things are made of is only about 4% of the universe. Dark matter, which has a gravitational effect but otherwise undetectable + what they dubbed dark energy is the rest. Blushes all around.