The researchers claim to have found 10 dark gas giantsfloating at the heart of our Milky Way without any nearby star to illuminate them. Astronomers have long suspected such rogueplanets existed, but this is the first evidence, and the Japanese team believe there could be as many out there as there are stars, a finding likely to shock many.

How they came into being is unclear. One theory is that they may be cast-outs, forgotten worlds ejected from infant solar systems bygravitational forces or interplanetary collisions.

Strictly speaking, the objects aren't even planets, as by definition planets orbit a star or the remains of one. But should the researchers have their calculations right, then strange dark orbswhich look very much like planets are out there, far far from any shining star.