What the heck is Dark Matter and what's Triangulum II?

Astronomer discovers nearby galaxy made almost entirely of dark matter.

Scientists have discovered a galaxy that may be composed mostly of dark matter. Dark matter is an elusive substance that is yet to be described by scientists. They know what it does, but not what it is. The discovery could help solve the mystery.

LOS ANGELES, CA (California Network) - By all conventional estimates, the Milky Way galaxy shouldn't exist. Decades ago, when scientists began to study the motions of other galaxies, they discovered something alarming: there wasn't enough mass to hold all the stars together in a galaxy. By their calculations, clustered galaxies, and their stars should all fly into deep space. Was there an error in their calculations?

It turned out there wasn't, instead the galaxy has much more matter than they could detect. Scientists have found they can measure the presence of this elusive matter, but they cannot identify it. Is it dust? Subatomic particles? Scientists called it "dark matter."

As scientists expanded their observations, they found that most of the matter in the galaxy, as much as 80 percent, is dark matter.

For decades, dark matter has proven one of the most elusive mysteries in astronomy, perhaps until now. Scientists have discovered that a tiny satellite galaxy of the Milky Way, just 117,000 light years away, has an incredible concentration of dark matter.

The galaxy is called Triangulum II and it has just about 1,000 stars. Yet the galaxy moves as if it has a lot more mass. This is the telltale cosmic fingerprint of dark matter. In fact, scientists think Triangulum II may have more dark matter than any other object they have observed.

The discovery was made when Caltech astronomer Kevin Kirby was making observations of the half-dozen stars in the galaxy's center. The measurements of these stars can reveal a galaxy's mass. However, in this case, the mass suggested by these measurements was much greater than what was expected.

A follow up study will now be performed to see if dark matter is truly present there.