The Milky Way Galaxy Is Distorting And We Don't Know Why

Something is pulling at the edge of the Milky Way, causing a “galactic warp” at the edge of our galaxy, as pointed out in a new study on Monday.

There are about 250 billion stars in the Milky Way clustering in spiral arms and swirling around a black hole at the center. However, astronomers have spotted another dynamic that occurs in the far reaches of the galaxy, where the galactic disk becomes flared, wobbly, or otherwise distorted.

A team of astronomers and astrophysicists, with the aim of figuring out what’s causing the outer warping of the Milky Way, measured the motions of 12 million stars observed through the Gaia space telescope. The team’s lead, astrophysicist Eloisa Poggio from the Italian National Institute for Astrophysics, said:

“Our Milky Way presents a unique case study for galactic warps, thanks to detailed knowledge of its stellar distribution and kinematics. However, the cause and dynamic nature of the warp of our Galaxy have remained unclear due to a lack of kinematic constraints.”

That means it wasn’t until a few years ago that scientists began to model the outer warping of the Milky Way in detail, thanks to advanced observational techniques. For example, last year, a team made a 3D map of the warp by measuring 2,300 Cepheids variables, a type of ultra-radiant stars.

Now, Poggio and the team have built on these models with the help of the 2018 data amount from the Gaia satellite, which has been creating the most comprehensive catalog ever of the observable universe.

With this volume of observation, the team was able to measure the stars’ motions to trace the kinematic signature of the Milky Way’s warp. Poggio said:

 “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 centre of the Milky Way in 600 to 700 million years. That’s much faster than what we expected based on predictions from other models.”

The team is using Gaia’s data from 2018 to constrain the possible mechanism behind the galaxy’s warp. Some suggested explanations include the longstanding torques that emerged from mismatched axial motions of the galactic and the disk halo, or the tidal forces from the Milky Way’s satellite galaxies, which could pull the disk. From their model, Poggio and her colleagues found that the pull from a satellite galaxy could mostly be responsible for the warp though they need more research and observations to confirm this.

“The direction and magnitude of the warp’s precession rate favor the scenario that the warp is the result of a recent or ongoing encounter with a satellite galaxy, rather than the relic of the ancient assembly history of the galaxy.”

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