Our Milky Way galaxy may have a mysterious, invisible neighbor galaxy that contains an overwhelming amount of dark matter, according to National Geographic

The dark galaxy, dubbed "Galaxy X" by the scientists who detected it, was found using a technique similar to that used 160 years ago to predict the existence of Neptune. The planet's gravitational effect on Uranus was seen long before it was viewed through a telescope. In fact, gravitational effects are typically the only way to detect dark matter because it emits no light. 

"This is basically a new method to render dark galaxies visible," said Sukanya Chakrabarti, the University of California at Berkeley researcher who devised the new technique.

Chakrabarti's technique is capable of detecting dim dwarf galaxies as small as a thousandth the mass of the Milky Way, and she believes confirming the existence of Galaxy X could lead to the discovery of more nearby dark matter galaxies. In fact, Chakrabarti thinks dark matter galaxies could be lurking in great numbers just outside the Milky Way.

Although scientists believe dark matter makes up 80 percent of the mass of the universe, it remains a theoretical entity for the very reason that it cannot be seen. There's a chance that Galaxy X may be uniquely different in this regard, though. It might contain a sprinkling of dim stars detectable if the search is conducted using dust-penetrating infrared light. If those dim stars still flicker, they would provide a hint of proof for those who have to see it to believe it.

"Say you're looking for a car with very dim headlights, in the fog," she said. "If you know approximately where to look, you would have a better chance of finding it."

But even if Galaxy X doesn't contain any dim evidence of its existence, Chakrabarti is still optimistic that her technique will provide invaluable clues about the mysterious nature of dark matter, or about whatever other mysterious forces might exist to explain scientists' calculations.

"We still stand to learn something very fundamental," she said.