It is somewhat unclear, though, whether the ultimate source of this gas is a remnant halo (as proposed by Oort), deep intergalactic space, or even a small dwarf galaxy that the Milky Way swallowed.

• 虽然如此，我们尚不清楚这些气体的终极来源，究竟是如欧特所倡议的星系冕残留物，是来自星系际空间深处，甚或是被银河所吞噬的小型矮星系。