2023-11-29 アリゾナ大学
◆研究者たちは「銀河噴水」や低質量星の新たなメカニズムを提案しています。この発見は、地球の生命に必要な要素が銀河の外側にも存在する可能性を示し、地球外の生命を探す際に新たな展望を提供しています。今後の研究で、リンの生成と分布に関する通説が更新される可能性があります。
＜関連情報＞
- https://news.arizona.edu/story/case-missing-phosphorus-astronomers-find-life-ingredient-galaxys-edges
- https://www.nature.com/articles/s41586-023-06616-1
銀河の端にあるリン含有分子POとPN Phosphorus-bearing molecules PO and PN at the edge of the Galaxy
L. A. Koelemay,K. R. Gold & L. M. Ziurys
Nature Published:08 November 2023
DOI:https://doi.org/10.1038/s41586-023-06616-1
Abstract
Despite its importance in planet formation and biology, phosphorus has been identified only in the inner 12 kpc of the Galaxy. The study of this element has been hindered in part by unfavourable atomic transitions. Phosphorus is thought to be created by neutron capture on Si and Si in massive stars, and released into the interstellar medium by Type II supernova explosions. However, models of galactic chemical evolution must arbitrarily increase the supernovae production to match observed abundances. Here we present the detection of gas-phase phosphorus in the Outer Galaxy through millimetre spectra of PO and PN. Rotational lines of these molecules were observed in the dense cloud WB89-621, located 22.6 kpc from the Galactic Centre. The abundances of PO and PN in WB89-621 are comparable to values near the Solar System. Supernovae are not present in the Outer Galaxy, suggesting another source of phosphorus, such as ‘Galactic Fountains’, where supernova material is redistributed through the halo and circumgalactic medium. However, fountain-enriched clouds are not found at such large distances. Any extragalactic source, such as the Magellanic Clouds, is unlikely to be metal rich. Phosphorus instead may be produced by neutron-capture processes in lower mass asymptotic giant branch stars which are present in the Outer Galaxy. Asymptotic giant branch stars also produce carbon, flattening the extrapolated metallicity gradient and accounting for the high abundances of C-containing molecules in WB89-621.
