Our home galaxy, the Milky Way, doesn’t have enough satellites – smaller galaxies in orbit around it. Unless it has too many. That’s the conundrum facing the scientists who study how galaxies are born.

So far, astronomers have discovered about 60 galaxies orbiting the Milky Way. Most of them are much smaller than the Milky Way. That makes them faint and hard to find. But models of galaxy formation say the Milky Way should have more than 200 satellites. The difference has been called the “missing satellite problem.”

The models are based on ideas about dark matter. It appears to make up about 85 percent of all the matter in the universe. But it doesn’t produce any energy that we can see. It reveals its presence only through its gravitational pull on the visible matter around it.

In the early universe, dark matter should have congregated in big clumps. They pulled in normal matter, which formed stars and galaxies. Smaller clumps should have given birth to smaller galaxies around the big ones. But the number of smaller galaxies hasn’t matched those predictions.

A recent search of a small patch of sky discovered several new small galaxies. Based on that, researchers suggested the Milky Way could have about 500 satellites.

Many of these little guys could have been absorbed by the Milky Way over the eons. Or perhaps hundreds of them still await discovery – tiny galaxies orbiting the giant Milky Way.

Script by Damond Benningfield