First age-map of the heart of the Milky Way

The first large-scale age-map of the Milky Way shows that a period of star formation lasting around 4 billion years created the complex structure at the heart of our galaxy. The results will be presented by Marina Rejkuba at the European Week of Astronomy and Space Science (EWASS) in Liverpool on Tuesday, 3rd April.

The Milky Way is a spiral galaxy with a bulge at the centre, thousands of light years in diameter, that contains about a quarter of the total mass of stars. Previous studies have shown that the bulge hosts two components: a population of metal-poor stars that have a spherical distribution, and a population of metal-rich stars that form an elongated bar with a "waist", like an x or a bi-lobed peanut. However, analyses of the ages of the stars to date have produced conflicting results. Now, an international team led by astronomers from the European Southern Observatory (ESO) have analysed the colour, brightness and spectral information on chemistry of individual stars to produce the age-map of the Milky Way.

Source

 

Credit: ESO/M. Rejkuba/F. Surot Madrid/E. Valenti

The infrared map constructed from the VISTA Variables in the Via Lactea (VVV) survey of the inner Milky Way showing the three areas studied.

Source / Image Courtesy

 

Credit: ESO/M. Rejkuba/F. Surot Madrid/E. Valenti

One of the three boxes studied, showing a superposition of almost 3 million stars belonging to different Milky Way structures along the line of sight: the Milky Way disk, as well as the stars belonging to the bulge region.

Source / Image Courtesy

 

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

Artist's impression showing the peanut shaped structure in the central bulge.

Source / Image Courtesy

 

This 3D view shows red giant stars strewn throughout the Milky Way. The sample is embedded in a simulation of a Milky Way-like galaxy. The youngest stars are shown in blue, the oldest stars in red, and middle-aged stars in green. The 70,000 stars shown here come from the APOGEE survey, part of the larger Sloan Digital Sky Survey.

 

Proud parents chart the growth of their children, but astronomers from the Sloan Digital Sky Survey have taken on a bigger task: charting the growth of our own Milky Way.

 

Animation of a barred galaxy like the Milky Way showing the presence of an X-shaped bulge.

The X-shape extends to about one half of the bar radius. It is directly visible when the bar is seen from the side, but when the viewer is close to the long axis of the bar it cannot be seen directly and its presence can only be inferred from the distribution of brightnesses of stars along a given direction.

 

WISE allsky map of the sky showing the Milky Way Galaxy. The central circle indicates the centre of the Galaxy and the inset shows an enhanced view of the x-shaped structure. Credit: NASA/JPL-Caltech; D. Lang/Dunlap Institute
While taking a second look at data collected by the Wide-field Infrared Survey Explorer (WISE) space telescope, two scientists confirmed the presence of an X-shaped star structure in the Milky Way’s central bulge.

The existence of the structure has been a subject of debate among astronomers. Until now, there was no direct evidence for it although computer models, observations of the galaxy, and even observations of other galaxies strongly suggested its presence.