This odd shape was mapped by using public data from European Southern Observatory (ESO)'s VISTA survey telescope, along with measurements of motions of hundreds of faint stars in the central bulge. (Agencies)
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.
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.
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.
"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," said Christopher Wegg (MPE), 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," he said.
"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," added Ortwin Gerhard, the co-author of the first paper.
The second international team, led by Chilean researcher
Sergio Vasquez, compared images taken eleven years apart with the MPG/ESO 2.2-metre telescope to measure the tiny shifts due to the motions of the bulge stars across the sky.
These were combined with measurements of the motions of the same stars towards or away from the Earth to map out the motions of more than 400 stars in three dimensions.
"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!" Vasquez said.
The astronomers believe that the Milky Way was originally a pure disc of stars which formed a flat bar billions of years ago. The inner part of this then buckled to form the three-dimensional peanut shape.
This odd shape was mapped by using public data from European Southern Observatory (ESO)'s VISTA survey telescope, along with measurements of motions of hundreds of faint stars in the central bulge.