It can be difficult to determine the volume of a large body or locate distant floating objects when you are swimming in it. This is also true for our galaxy.It is difficult to determine much of the Milky Way's size, contents, or three-dimensional structure from our position within it. There are many things that we don't know or can't calculate. But every once in a while, something happens that surprises us and makes us wonder: How did that happen? It's all here!The Cattail, a newly discovered structure, is exactly such a wonder. It's a long, curving gas curl that is so large that astronomers don't know if it's part of a galactic spiral arm.The Cattail, even if it's not the sign of a unmapped spiral arm is the largest filament of gas found in our galaxy to date. It was described in a paper accepted by The Astrophysical Journal Letters. The paper is available on arXiv's preprint server.A team of Chinese astronomers wrote in the paper that the structure was "apparently the furthest, largest giant filament in galaxy,""It remains to be determined how such a large filament is made at this extreme galactic location. Cattail could be an alternative part of a new arms, though it is puzzling how the structure doesn't fully follow the warp in the galactic disk.It's difficult to map the Milky Way three-dimensionally for several reasons. It's difficult to calculate the distances between cosmic objects. There is also a lot of stuff, so it can be difficult to determine if something is significant or just a random collection scattered along a line.Chong Li, an astronomer at Nanjing University, used the massive Five-hundred-meter Aperture Spherical radio Telescope to search for clouds of neutral nuclear hydrogen (HI) in order to identify the Cattail. These clouds are often found in spiral arms galaxies such as ours. By studying subtle differences between the hydrogen's light it is possible to map the Milky Ways' arms.The researchers used FAST in August 2019 to search for HI radio emission. They discovered a large structure. They were surprised to find out that the structure's velocity was constant with a distance of approximately 71,750 light years from the galactic centre - the outer regions in the galaxy.This distance, which is further than any known spiral arms in the region of the galaxy, would indicate that the thing is enormous, measuring approximately 3,590 light years in length and 675 in width, according to the FAST data.The researchers then combined their findings with data gathered from the HI4PI allsky HI survey to find that the distance could be even greater - up to 16,300 light years.This would make it more impressive than Gould's Belt gas structure, which is 9,000 light-years in length.The Cattail raises interesting questions. Gas filaments are found closer to the galactic centre and are often associated with spiral arms. It's not clear if the Cattail is a filament. However, it's possible that it formed outside the spiral arms of Milky Way.However, if it is a spiral arm, then that's also unusual. The galactic disc of Milky Way is warped and wobbly from a long-ago encounter with another galaxie. The shape of the Cattail is not perfect, however, as it would if it were a spiral arm.These peculiarities suggest that even if we didn't find the structure fascinating enough, it might be worth taking a closer look.The researchers stated that while these questions are still open to the existing data, the observations offer new insight into our understanding of galactic structure.The Astrophysical Journal Letters has accepted the research and it is now available on arXiv.
