The inner portions of the galactic halo — the outermost region of the Milky Way — have been mapped with a high level of accuracy. A new map of the halo’s outer regions has been updated with data collected during 2009 and 2018 by NASA and European Space Agency (ESA) missions. The all-sky map reveals the wake of the Large Magellanic Cloud (LMC), a dwarf galaxy, traveling through the region toward a collision course with the Milky Way in about 2 billion years.

This disturbance in the galactic force, about 200,000 light-years to 325,000 light-years from the center of the Milky Way, affords an opportunity to study dark matter. The wake observed in the new map is thought to be the outline of a dark matter wake trail forged by the LMC, which is theorized to slow down under the influence of gravity from dark matter. The orbit of the LMC will become steadily smaller, ending with a future Milky Way merger.

A paper on this cosmic finding is published in Nature, and additional information is available from NASA Jet Propulsion Laboratory.

The smaller structure is a wake created by the LMC’s motion through this region. The larger light-blue feature corresponds to a high density of stars observed in the northern hemisphere of our galaxy. Source: NASA/ESA/Jet Propulsion Lab-Caltech/Conroy et. al. 2021