ESO's VISTA survey telescope helps map the Centre of the Milky Way

This artist's impression shows how the Milky Way galaxy would look seen from almost edge on and from a very different perspective than we get from the Earth. 

The central bulge shows up as a peanut shaped glowing ball of stars and the spiral arms and their associated dust clouds form a narrow band. 

Credit: ESO/NASA/JPL-Caltech/M. Kornmesser/R. Hurt

Two groups of astronomers have used data from ESO telescopes to make the best three-dimensional map yet of the central parts of the Milky Way.

They have found that the inner regions take on a peanut-like, or X-shaped, appearance from some angles.

This odd shape was mapped by using public data from ESO's VISTA survey telescope along with measurements of the motions of hundreds of very faint stars in the central bulge.

One of the most important and massive parts of the galaxy is the galactic bulge. This huge central cloud of about 10 000 million stars spans thousands of light-years, but its structure and origin were not well understood.

Unfortunately, from our vantage point from within the galactic disc, the view of this central region—at about 27 000 light-years' distance—is heavily obscured by dense clouds of gas and dust.

Astronomers can only obtain a good view of the bulge by observing longer wavelength light, such as infrared radiation, which can penetrate the dust clouds.

Earlier observations from the 2MASS infrared sky survey had already hinted that the bulge had a mysterious X-shaped structure.

Now two groups of scientists have used new observations from several of ESO's telescopes to get a much clearer view of the bulge's structure.

The first group, from the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching, Germany, used the VVV near-infrared survey from the VISTA telescope at ESO's Paranal Observatory in Chile.

This new public survey can pick up stars thirty times fainter than previous bulge surveys. The team identified a total of 22 million stars belonging to a class of red giants whose well-known properties allow their distances to be calculated.

Christopher Wegg

"The depth of the VISTA star catalogue far exceeds previous work and we can detect the entire population of these stars in all but the most highly obscured regions," explains Christopher Wegg (MPE), who is lead author of the first study.

"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."