It appears to be so far the furthest and largest giant filament – an unspotted spiral arm in the galaxy.
Scientists have recently stumbled upon a new object in space, which has not been detected before, and an enormous trail of gas lurking in the galaxy, called Cattail. It is located 22 kiloparsecs – 7,1754 light-years from the middle of the Milky Way.
In a new study, due for publication in The Astrophysical Journal Letters, present on arXiv Chong Li and the team tried to explain that they used the Five-hundred-meter Aperture Spherical radio Telescope (FAST) to search for clouds of neutral atomic hydrogen (H I) in a region of sky located 1.4 kiloparsecs (4,566 light-years) from our sun.
No such cloud has been seen before in the Outer Scutum-Centaurus (OSC) arm or the outermost spiral arm. This body of gas is moving at approximately 150 Kilometer per second, therefore, it is believed that it would be located far behind the OSC. The researchers write in the paper,
The H I structure has a length of 1.1 kpc [3,588 lightyears], which appears to be so far the furthest and largest giant filament in the Galaxy and we name it Cattail.
Upon cross-referencing this observation with the HI4PI all-sky H I survey data, the team calculated that this entity is way bigger than previously estimated, that is around 5 kiloparsecs longer, which is roughly 16,310 light-years. Making this Cattail roughly five times as long as it is wide, an aspect ratio similar to other spiral arms. But it lacks the correct shape to be a spiral arm, that is, unalignment with the warped axis of the rest of the galaxy.
There are many rules that this structure tends to ignore, like its unusual size and extreme size, or the lack of signs of physical connection with any spiral arms of the Milky Way. So the team concluded that there are two possible explanations for Cattail, one is that it is a giant filament with a length of approximately 5kpc or it is a part of a new arm in the extreme outer galaxy.
The Cattail’s true nature and identity are still under question, and there are a lot of unanswered questions. “If Cattail is a gas filament located beyond the OSC, how is such a huge structure formed?” they ask. “Alternatively, if Cattail is part of a new spiral arm in the EOG, it is also puzzling that the new arm does not fully follow the Galactic warp.”