Astronomers Create Finest 3D Map Revealing Peanut-like Shape at the Galaxy's Heart

Two groups of astronomers teamed up creating the finest 3D map of the Milky Way galaxy with the help of ESO (European Southern Observatory) telescopes and discovered that its inner-region has a peanut-like shape or X-shape at the heart when viewed from some angles.

A 2MASS infrared sky survey done previously had hinted toward the mysterious shaped structure in the galactic bulge. The two groups of astronomers utilized the data from the ESO telescopes to create the finest three-dimensional map of the central parts of the Milky Way galaxy so far.

ESO's VISTA (Visible and Infrared Survey Telescope for Astronomy) telescope, which is situated at Chile's Paranal Observatory and has a 4.1 meter mirror, formulated this odd shape in the central bulge of our galaxy. Measurements of the motions of many extremely faint stars were surveyed by the VISTA telescope, which led to this finding.

"The depth of the VISTA star catalog far exceeds previous work and we can detect the entire population of these stars in all but the most highly obscured regions," explained Christopher Wegg, lead author of the first study from MPE, in a press release.

"From this star distribution we can then make a three-dimensional map of the galactic bulge. This is the first time that such a map has been made without assuming a model for the bulge's shape," Wegg added.

The galactic bulge, stretching over thousands of light-years, is considered to be one of the most significant parts of the galaxy. The origin and the structure of this enormous central cloud consisting of 10,000 million stars were not very clearly understood by the astronomers.

The galactic bulge is located at a distance of around 27,000 light-years from our point of view. It consists of dense dust clouds and gases, which makes it hard to accumulate precise information. Hence, the first group from the MPE (Max Planck Institute for Extraterrestrial Physics) located in Garching, Germany, used the VVV near-infrared survey from the VISTA telescope. Examining these dust clouds with lights having longer wavelength such as the infrared radiation aided the astronomers in getting a good view through the thick dust clouds and gases.

A total of 22 million stars belonging to a class of red giants were spotted by the team.

The inner shape of our Galaxy appears like a peanut in its shell when seen from the side and it appears like an extremely elongated bar when viewed from the top, explained Ortwin Gerhard, the co-author of the first paper and leader of the Dynamics Group at MPE.

"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," Gerhard stated.

The second international team was from Pontificia Universidad Católica de Chile, Santiago, Chile. The team was led by a Chilean PhD student Sergio Vásquez. This team compared various images taken by the MPG/ESO 2.2-metre telescope eleven years back to figure out the shape of the galactic bulge. The team noted minute alterations due to the motions of the bulge stars across the sky. These observations were merged with the measurements of the motions of the same stars heading towards or away from Earth in order to outline the motions of above 40 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," Vásquez said.

"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!" he concluded.

The astronomers assume that billions of years ago, the Milky Way was originally a pure disc of stars that formed a flat bar. The internal part of this flat bar then buckled to create the three-dimensional peanut structure observed by the researchers.