Astronomy: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]
In 2024 a subdwarf of spectral type sdT4 was identified as a possible member of the Helmi stream. The brown dwarf is called CWISE J155349.96+693355.2 has Vtan > 300 km/s and a poorly constrained radial velocity of +110±90 km/s.[4]
Ultra-metal-poor Star
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.[5]
Extragalactic planet
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.[6]
See also
References
- ↑ 1.0 1.1 Scientific American, "Extragalactic Expat: Newfound Exoplanet Likely Came from Another Galaxy", John Matson , 18 November 2010
- ↑ 2.0 2.1 "Amina Helmi, the "archeologist of the Milky Way," explains how our own galaxy could unlock the mystery of dark matter" (in en). 2017-12-12. https://www.fbbva.es/en/noticias/amina-helmi-the-archeologist-of-the-milky-way-explains-how-our-own-galaxy-could-unlock-the-mystery-of-dark-matter/. ""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. https://knowablemagazine.org/article/physical-world/2021/a-galactic-archaeologist-digs-milky-ways-history. Retrieved 4 August 2022.
- ↑ Burgasser, Adam J.; Schneider, Adam C.; Meisner, Aaron M.; Caselden, Dan; Hsu, Chih-Chun; Gerasimov, Roman; Aganze, Christian; Softich, Emma et al. (2 Nov 2024). "New Cold Subdwarf Discoveries from Backyard Worlds and a Metallicity Classification System for T Subdwarfs". The Astrophysical Journal 982 (2): 79. doi:10.3847/1538-4357/adb39f. Bibcode: 2025ApJ...982...79B.
- ↑ Placco, Vinicius; Limberg, Guilherme; Kennedy, Catherine; Christlieb, Norbert (2026 March 20). "HE 0144–4657: A Carbon-enhanced Ultra-metal-poor Star ([Fe/H ∼ −4.1) from the Helmi Stream Disrupted Dwarf Galaxy*"] (in English). The Astrophysical Journal Letters. https://iopscience.iop.org/article/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. doi:10.1051/0004-6361/201322132. Bibcode: 2014A&A...562A.129J.
 |  |
