Technically, “S1” is a stream of debris from a dwarf galaxy torn apart by the Milky Way’s gravity, passing through space. What S1 is pulling along with it, though, is being described in a far more dramatic way, as “a dark matter hurricane.” Scientists believe this companion stream of dark matter (DM) is hurtling through us right now at a jaw-dropping speed of 500 kilometers a second. Hence the “hurricane” metaphor. Is it time to head down into our quantum storm cellars? Not quite. This is dark matter, after all, material we can’t directly perceive and with which we can’t interact, so no worries. On the other hand, this blast of DM has the potential to afford us our best glimpse yet of the elusive stuff.
A team lead by Ciaran A. J. O’Hare developed a series of models that predicted what would happen as all of this DM came charging through our solar system, and published research presenting resulting signatures whose detection would signify S1 and its dark matter.
Astronomers have, over time, observed about 30 such streams wending their way across the heavens. S1 was first discovered about a year ago by the Gaia satellite. What makes it exceptionally interesting, though, as the paper says, is that the “stars in S1 impact on the Solar System at very high speed almost head-on. A coherent stream of DM associated with S1 hits the Solar System slap in the face.”
The reason scientists suspect S1 of having a companion stream of dark matter is that its source galaxy seems to have been similar to an existing galaxy, the Fornax galaxy. The paper asserts, “If this prediction is true then the S1 stellar stream must be accompanied by a substantial DM stream.”