Helmi stream


The Helmi Stream is a stellar stream of the Milky 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 after Amina Helmi, who discovered this stellar stream after noticing this group of stars all moving at the same speed and in the same direction.[2] The Helmi Stream discovery affirmed theories that the merging of galaxies did not play a significant role in creating the giant structures of the Milky Way galaxy.[2]

Extragalactic planetEdit

The Helmi stream was home to the first planet purportedly of extragalactic origin, orbiting the star HIP 13044.[1] Further analysis of radial velocity data failed to confirm the discovery.[3]

See alsoEdit


  1. ^ a b Scientific American, "Extragalactic Expat: Newfound Exoplanet Likely Came from Another Galaxy", John Matson , 18 November 2010
  2. ^ a b "Amina Helmi, the "archeologist of the Milky Way," explains how our own galaxy could unlock the mystery of dark matter". FBBVA. 12 December 2017. Retrieved 7 November 2019.
  3. ^ Jones, M. I.; Jenkins, J. S. (2014). "No evidence of the planet orbiting the extremely metal-poor extragalactic star HIP 13044". Astronomy & Astrophysics. 562: id.A129. arXiv:1401.0517. Bibcode:2014A&A...562A.129J. doi:10.1051/0004-6361/201322132.