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][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]

Extragalactic planet

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.[4]

See also

References

  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. The idea had already been mooted that the merging of small galaxies could have played a major part in forming today's giant structures. Helmi developed the tools that were able to test this hypothesis and confirm that it held true, at least for the Milky Way.
  3. ^ Skibba, Ramin (10 June 2021). "A galactic archaeologist digs into the Milky Way's history". Knowable Magazine. doi:10.1146/knowable-060921-1. S2CID 236290725. Retrieved 4 August 2022.
  4. ^ 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. S2CID 55365608.


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