One of the brightest stars in our sky probably came from a small galaxy that was swallowed up by the Milky Way, according to a Canadian researcher.

Arcturus is the fourth brightest star, shining a soft orange light in northern spring skies. It is 36 light years away from Earth.

University of Victoria astrophysics Prof. Julio Navarro and his Dutch and Australian colleagues concluded Arcturus is an alien star, challenging the traditional theory of galaxy formation.

Prof. Julio Navarro with image(Courtesy: University Of Victoria)

Traditionally, galaxies were thought to develop in isolation after the collapse of a giant cloud of gas and dust.

To Navarro, the explanation seems too simplistic. He thinks galaxies may form when smaller ones are disrupted, trapped and swallowed.

• FROM JULY 5, 2001: Andromeda galaxy is a cannibal: astronomers

The team used computer simulations to study movements of Arcturus and its associated stars.

"The main clue is that they follow paths that differ strongly from that of our sun," said Navarro in a release.

The majority of stars in the Milky Way follow a circular orbit around the centre of the galaxy. Arcturus takes an elliptical orbit.

The difference suggests Arcturus formed under different conditions than most in the Milky Way: intergalactic cannibalism.

In this week's issue of The Astrophysical Journal Letters, they conclude our Milky Way galaxy swallowed Arcturus about 10 billion years ago.

To back up their theory, they point to new evidence suggesting the Milky Way is currently swallowing up two other galaxies, the Sagittarius dwarf galaxy and the Canis major galaxy.

Astronomers say the Milky Way leaves behind a tell-tale stream of stars from small galaxies it's engulfed.