Dark matter. It's something we've heard a lot about in recent months, but it's also something that's been a mystery to astrophysicists for years. 

"Dark matter is a term used to describe matter that's part of a structure of the universe that we can't detect in any way," said Derrick Pitts, chief astronomer at The Franklin Institute in Philadelphia. "We're talking about what you might call substance, but it doesn't have any characteristics of substance that astronomers would typically identify matter to have."

Pitts says astronomers really depend on being able to detect energy in space, but this is one thing that gives us no signature whatsoever, except for the fact that it "pushes on stuff."

"We can calculate exactly what that push is and we can figure out how much of that push is around in the universe and we can definitely see the effect that push is having," said Pitts.

Astronomers estimate that four to five percent of the matter of the universe is a combination of us, the planets, stars, galaxies, dust and energy. The other 95 to 96 percent is dark matter and dark energy.

In an effort to try to detect some of this dark matter, the International Space Station mounted an alpha magnetic spectrometer to its exterior, which is set to detect cosmic rays coming from all kinds of objects in space. The analysis of these hits may lead us to a better understanding about the nature of dark matter.

"There have been hundreds of millions of hits, but can we actually determine that these hits are directly related to dark matter activity?" said Pitts. "If they are, then we have a way to detect the existence of dark matter and trace its interaction around the universe."

Pitts says answering the question about dark matter has to be one of the most exciting challenges that astrophysicists had before them because it brings him back to one main point:

"If dark matter and its companion, dark energy, are so much more dominant in the structure and behavior of the universe than the four percent of matter that makes up the stuff that we know," said Pitts, "then to me, it suggests the universe is much more about the dark matter than it is about us. You can consider the "us" to be a byproduct of this other process that's governed by dark matter."

Pitts says the puzzle pieces are beginning to be pulled together, which could help to answer many other big picture questions, such as whether this is the only universe and if there are other universes that exist adjacent to ours that we can't see.