September 12, 2013
Astronomers Find Peanut Sitting In Middle Of Milky Way
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Lee Rannals for redOrbit.com - Your Universe Online
Astronomers, publishing two papers in the journal Astronomy & Astrophysics, say they've found a peanut sitting in the heart of the Milky Way galaxy.
Two teams used data from European Southern Observatory (ESO) telescopes to create a three-dimensional map of the central parts of the Milky Way. While crafting the map they found that the inner regions of the galaxy take on a peanut-like appearance from certain angles.
"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," Ortwin Gerhard, the coauthor of the first paper and leader of the Dynamics Group at Max Planck Institute for Extraterrestrial Physics (MPE), said in a statement. "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."
The astronomers believe the Milky Way was originally a pure disc of stars that formed as a flat bar billions of years ago. The inner part of our galaxy then buckled to form the three-dimensional peanut shape seen in the team's observations.
Our view of this region is heavily obscured by dense clouds of gas and dust, so astronomers must observe it using longer wavelength light, such as via infrared radiation. This wavelength is capable of penetrating the dust clouds and revealing what lies beneath.
One group mapping out the Milky Way used the VVV near-infrared survey from the VISTA telescope at ESO's Paranal Observatory in Chile. This survey is able to pick up stars thirty times fainter than previous bulge surveys. The astronomers were able to map out 22 million stars belonging to a class of red giants using VISTA.
“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, from MPE and 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.”
The second group compared images taken eleven years apart with the MPG/ESO 2.2-meter telescope. They measured tiny shifts due to the motion of the bulge stars across the star and combined it 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 the 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 Chilean PhD student Sergio Vásquez, who authored the second paper. “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!”