From Emission to Absorption: The Fascinating FAST Observations of the OH 18-cm Lines from Comet C/2025 A6 - Astrobiology
Imagine witnessing a comet transform right before your eyes! Between October 23 and November 8, 2025, our team utilized the FAST telescope, outfitted with an ultra-wideband receiver, to make a groundbreaking discovery: we detected the OH 18-cm lines emitted by comet C/2025 A6 for the very first time.
What’s truly intriguing is how the OH lines changed from emitting radiation to absorbing it during our observation period. This switch occurred between October 23 and November 5, primarily due to fluctuations in the comet's heliocentric velocity—the speed at which it moves relative to the Sun. To analyze these variations, we employed trapezoidal fitting techniques on the profiles of the OH lines, allowing us to calculate the expansion velocities of water vapor being released. Remarkably, we found that these velocities increased as the comet drew closer to the Sun.
Drawing from our findings, we were able to estimate the OH production rates for comet C/2025 A6 on specific dates: October 23, October 26, November 4, and November 5. The results were compelling, showing a clear upward trend in OH production as the comet approached the Sun, suggesting a dynamic interaction between the comet and solar radiation.
This research was conducted by a dedicated team including Dongyue Jiang, Lei Qian, Minglei Guo, Qiaoli Hao, Menglin Huang, Peng Jiang, Hongfei Liu, Chun Sun, Xingyi Wang, Qingliang Yang, Naiping Yu, Lei Zhao, Yutao Zhao, Liyun Zhang, Yichi Zhang, Tongjie Zhang, and Zhichen Pan.
For those interested in the detailed findings, the study comprises 7 pages, featuring 2 figures and 3 tables that illustrate our observations and the derived data.
This work falls under the categories of Earth and Planetary Astrophysics (astro-ph.EP) and Astrophysics of Galaxies (astro-ph.GA). If you’d like to delve deeper into this exciting research, it can be cited as arXiv:2512.21969 [astro-ph.EP], with this version available as arXiv:2512.21969v1 [astro-ph.EP]. You can access it directly via https://doi.org/10.48550/arXiv.2512.21969.
