And we thought you guys were our best friends forever!

*sniff*

Two nearby galaxies - long thought to be true companions of the Milky Way - may instead be drifters, passing through the cosmic neighbourhood.

Astronomers say the Magellanic Clouds may be moving too fast to be gravitationally bound to our galaxy.

If the clouds were satellites of our galaxy, the Milky Way would contain twice as much mass as is thought.

[snip]

The researchers say there are two possible explanations for the unexpectedly high 3D velocities of the dwarf galaxies.

The Milky Way could be twice as massive as previously thought: this excess mass, pulling on the clouds, would be required to keep them gravitationally bound.

Alternatively, the Large and Small Magellanic Clouds might not be bound to our galaxy after all.

If previous calculations of the Milky Way's mass are correct, it does not possess enough mass to hold on to its companions.

In a few billion years, they will escape the clutches of our galaxy.

"The Magellanic Clouds may not be true companions of the Milky Way," Dr Kallivayalil said. "Perhaps they are travellers, just passing through our cosmic neighbourhood."