Milky Way Center Shaped like a Peanut

Scientists now have a better understanding of the central galactic bulge, the huge cloud of stars at the center of our galaxy, finding that the shape of the central bulge looks rather like a peanut.

About 10,000 million stars, spanning a distance of thousands of light years, burn in the galactic budge. At its center, about 27,000 light years away from Earth is a supermassive black hole.

Observing the central galactic bulge from Earth has always been a challenge because of the great distance and because the view is heavily obscured by a dense cloud of gas and dust.

By compiling data from the Two Micron All Sky Survey (2MASS) project, which had previously indicated the bulge had an X-shape, with observations from publicly available data from the from the European Southern Observatory (ESO) VISTA survey telescope, astronomers have learned more about the shape of the center of our galaxy.

"We find that the inner region of our galaxy has the shape of a peanut in its shell from the side, and of a highly elongated bar from above", said Ortwin Gerhard, the coauthor of the first paper and leader of the Dynamics Group at Max Planck Institute for Extraterrestrial Physics (MPE) in Garching, Germany. "It is the first time that we can see this clearly in our own Milky Way, and simulations in our group and by others show that this shape is characteristic of a barred galaxy that started out as a pure disc of stars."

A second team of astronomers reached a similar conclusion by a different method.

Led by Sergio Vásquez, of the Pontificia Universidad Católica de Chile, Santiago, Chile, the second research team compared images of the central bulge 11 years apart using the MPG/ESO 2.2-meter telescope. The instrument was able to measure tiny shifts in the image due to the motions of the bulge stars across the sky. These were combined with measurements of the motions of the same stars toward or away from the Earth to map out the motions of more than 400 stars in three dimensions.

"This is the first time that a large number of velocities in three dimensions for individual stars from both sides of the bulge been obtained," said Vásquez. "The stars we have observed seem to be streaming along the arms of the X-shaped bulge as their orbits take them up and down and out of the plane of the Milky Way. It all fits very well with predictions from state-of-the-art models!"