In August 2019, the researchers used FAST to look for HI radio emissions, and the data revealed what appeared to be a large structure. When they calculated how fast the structure was moving, they got a surprise: its velocity was consistent with a distance of around 71,750 light-years from the galactic center - the outer regions of the galaxy.

That distance - farther than any known spiral arms in that region of the galaxy - would mean the thing is absolutely huge, with a size of around 3,590 light-years in length and 675 light-years in width, based on the FAST data. But then, when the researchers combined their findings with data from the HI4PI all-sky HI survey, they found that it could be even larger still - as much as around 16,300 light-years in length.

That would make it even more colossal than the gas structure known as Gould's Belt, which was recently found to be 9,000 light-years long.

https://einsteinathome.org/content/my-thoughts-cattail-qe-cattail-space-object-astronomers-detected-huge-new-structure-milky-wa

This was cited by QuantumHelos on the Einstein forum. It seems applicable here too.