Randall suggests that there’s a whole disk of dark matter in our own galaxy. For it to have an effect on us it would need to be roughly aligned with the visible disk of the Milky Way so that the solar system oscillates around it as it travels around the galactic centre. But this is problematic because to be able to explain observations made so far, cosmologists believe dark matter would form large spherical halos around galaxies rather than disks.
To get around this, we need to make dark matter weirder than it already is. Randall suggests that there is more than one type of dark matter in the form of a “contamination”, which she says could comprise 5-10% of the total dark matter. This kind of dark matter is different because it can interact with itself just like normal matter does. While the majority of dark matter can flow through itself without stopping, this special so-called “dissipative” dark matter can halt itself from moving and thereby form a galactic disk, like normal matter does. But, as Randall admits in her research papers, we do not know for sure that such dark matter would form a disk.
Even if it did, there is no reason why this dark disk should be aligned with the visible disk of the Milky Way, which it would have to do for it to unleash a huge comet towards the Earth.