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, and 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]
Ultra-metal-poor star
[edit]In 2026 an ultra-metal-poor star was discovered in the Helmi stream dubbed HE 0144−4657. This star is believed to have formed in a gas cloud enriched by a Population III star explosion of ~50 solar masses before the dwarf galaxy collided with the Milky Way.[4]
Extragalactic planet
[edit]The Helmi stream was briefly believed to be home to the first discovered planet purportedly of extragalactic origin, orbiting the star HIP 13044.[1] However, further analysis of radial velocity data failed to confirm the discovery.[5]
See also
[edit]References
[edit]- 1 2 "Extragalactic Expat: Newfound Exoplanet Likely Came from Another Galaxy", John Matson, Scientific American. 18 November 2010
- 1 2 "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.
- ↑ 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.
- ↑ Placco, Vinicius; Limberg, Guilherme; Kennedy, Catherine; Christlieb, Norbert (20 March 2026). "HE 0144–4657: A Carbon-enhanced Ultra-metal-poor Star ([Fe/H] ∼ −4.1) from the Helmi Stream Disrupted Dwarf Galaxy*". The Astrophysical Journal Letters. 1000: L34. arXiv:2601.15974. doi:10.3847/2041-8213/ae4dea.
- ↑ 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.