• The Milky Way's disc is not flat but warped
  • ESA's Gaia suggests the warp might be caused by a collision with another galaxy
  • It is possible that the galactic collision happened recently or is still ongoing

Astronomers have known for decades that the Milky Way's disc is warped. New data from the Gaia satellite suggest that the warp may be caused by a recent or ongoing collision with another galaxy.

Milky Way's Warp

Unlike in other barred spiral galaxies, the Milky Way's disc is not flat but is warped upwards on one side and downwards on the other side. Astronomers have known about this warp since the 1950s and, since then, they have debated about what exactly is causing it.

Theories vary from a dark matter halo bending the Milky Way's galactic disc to the influence of an intergalactic magnetic field and, now, researchers using the second data release from the European Space Agency's (ESA) Gaia satellite adds another to the list.

"We measured the speed of the warp by comparing the data with our models. Based on the obtained velocity, the warp would complete one rotation around the center of the Milky Way in 600 to 700 million years," study lead author Eloisa Poggio of the Turin Astrophysical Observatory said. "That's much faster than what we expected based on predictions from other models, such as those looking at the effects of the non-spherical halo."

Galactic Collision

This suggests that the warp is being caused by something more powerful than earlier theories suggested. According to the researchers, it is possible that this other, more powerful thing causing the warp might be a collision with another galaxy.

It is so far unclear exactly when this collision occurred or began but, evidence suggests that the event might have happened relatively recently or perhaps might still be ongoing. It is also unclear what galaxy the Milky Way may be colliding with but one of the strong contenders is the Sagittarius dwarf galaxy, which astronomers believe is gradually being absorbed by the Milky Way.

This galactic event, researchers assure, has no direct, noticeable effects on the life on Earth.

In its six years of being active, Gaia has been responsible for significant revelations of previous collisions between Milky Way and other galaxies. As it continues to collect accurate data on more than one billion stars in the sky, Gaia is expected to produce the most accurate 3D map of the Milky Way yet.