TheHelmi Stream is astellar stream of theMilky Way galaxy. It started as a dwarf galaxy, now absorbed by the Milky Way as a stream. It was discovered in 1999, is formed of old stars deficient in heavy elements, and has a mass of 10 to 100 million solar masses. It was absorbed by the Milky Way some 6 to 9 billion years ago.[1]
The stream was named afterAmina Helmi, who discovered this stellar stream after noticing this group of stars all moving at the same speed and in the same direction.[2][3] The Helmi Stream discovery affirmed theories that the merging of galaxies played a significant role in creating the giant structures of the Milky Way galaxy.[2]
The Helmi stream was briefly believed to be home to the first discoveredplanet purportedly ofextragalactic origin, orbiting the starHIP 13044.[1] However, further analysis of radial velocity data failed to confirm the discovery.[5]
