Stars Orbit in Peanut Shells at the Center of the Milky Way Galaxy

Just two months ago, astronomers created a new 3D map of the stars at the center of our Galaxy. Now, they've found out a little bit more about these stars. While previous models suggested that they moved in banana-like orbits, researchers have now discovered that they probably move in peanut-shell or figure of eight-shaped orbits.

This finding is actually pretty important in the grand scheme of things. Astronomers develop theories of star motions to not only understand how the stars in our Galaxy are moving today but also how our galaxy formed and evolves over time. The Milky Way is shaped like a spiral, with a region of stars at the center known as the "bar." Because of its shape, there's a bulge in the middle of the region that expands out vertically.

In order to learn a little bit more about the stars at this center bulge, the researchers created a mathematical model. As the stars go around in their orbits, they also move above or below the plane of the bar. When stars cross the plane, they receive a small push. At the resonance point, which is a point a certain distance from the center of the bar, the timing of the pushes on the stars is such that this effect is strong enough to make the stars move up higher above the plane. These stars are then pushed out from the edge of the bulge.

Using computer simulations, the researchers were able to determine that peanut-shell shaped orbits were consistent with the effect of this resonance. This orbit could also give rise to the observed shape of the bulge, which was also like a peanut-shell.

"It is hard to look back into the past of our galaxy and know what was there, but simulations can give us clues," said Alice Quillen, one of the researchers, in a news release. "Using my model I saw that, over time, the resonance with the bar, which is what leads to these peculiarly shaped orbits, moves outwards. This may be what happened in our Galaxy."

The findings reveal a little bit more about how our Galaxy functions. More specifically, it paves the way for future research, which could help answer questions about how the Milky Way was first created and how it evolved.

The findings are published in the journal Monthly Notices of the Royal Astronomical Society.