Our Milky Way is a galaxy with multiple spiral arms emanating from a central disk. The empty-looking halo lies outside of these swirling arms. But there may be more to the halo than meets the eye.
The halo, which hosts a small population of stars, is also thought to contain a lot of dark matter. This mysterious substance, which is invisible and has eluded scientists for decades, is thought to comprise most of the mass in the universe.
A small neighboring galaxy, known as the Large Magellanic Cloud, orbits the Milky Way. The data used to create the map revealed that, like a ship, the Large Magellanic Cloud has cut through the Milky Way’s outer halo. This disturbance has left a rippling wave of stars behind the Large Magellanic Cloud, which is in the halo.
A collision of galaxies
Currently, the Large Magellanic Cloud is 160,000 light-years from Earth, and it only has about a quarter of the mass of our giant galaxy.
The wake created by the Large Magellanic Cloud is about 200,000 light-years to 325,000 light-years from the galactic center.
While previous research suggested its existence, this new data provides confirmation, as well as the most detailed and accurate map of the galaxy’s outskirts.
In the image, the strip in the middle represents a 360-degree view of our galaxy overlaying a map of the galactic halo. A bright wave in the bottom left of the image is the wake of stars, and to the right is the Large Magellanic Cloud and the path it is taking.
A large, light blue feature in the top right shows a high concentration of stars in our galaxy’s northern hemisphere.
Understanding dark matter
The ripple left by the dwarf galaxy’s movement is also an opportunity to study dark matter. Even though dark matter is invisible, it provides structure throughout the universe — including the foundation for galaxies.
So if the Large Magellanic Cloud can cut through the Milky Way’s halo and leave a wave of stars, the same ripple should essentially act as an outline of the dark matter.
Dark matter is essentially pulling on the Large Magellanic Cloud to slow it down, shrinking the dwarf galaxy’s orbit around the Milky Way and causing the eventual collision.
While it sounds violent, galactic collisions are what have created the massive galaxies populating our universe — and our own galaxy has previously experienced mergers before.
“This robbing of a smaller galaxy’s energy is not only why the (Large Magellanic Cloud) is merging with the Milky Way, but also why all galaxy mergers happen,” said Rohan Naidu, study co-author and a doctoral student in astronomy at Harvard University, in a statement. “The wake in our map is a really neat confirmation that our basic picture for how galaxies merge is on point!”