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Spitzer glimpses into
Milky Way outback

Posted: 29 July 2010

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New images from the Spitzer Space Telescope survey GLIMPSE360 have revealed a treasure trove of gems scattered around the suburbs of the Milky Way, including some unexpectedly massive young stars.

The new survey is an extension of the original GLIMPSE (Galactic Legacy Infrared Mid-Plane Survey Extraordinaire) that focused on the Galaxy's bustling hub of stars and black hole embedded in the centre. Now the attention shifts to the suburbs, where the remaining half of the Milky Way's disc out to its edge will fall under scrutiny.

"It's like looking into the wilderness of our Galaxy," says Barbara Whitney, principal investigator for the survey. "While mapping the stars and dust out there, we hope to answer some major questions about an environment that is very different from the inner Milky Way."

Image: NASA/JPL-Caltech/2MASS/B. Whitney (SSI/University of Wisconsin).

One of the questions to be answered is how stars can be born in these distal regions that have a lower concentration of star-forming ingredients than the centre of the Galaxy. For example, in the image above, star-forming region BG2107+49 hosts swarms of young stars in the making that are ten to twenty times the mass of our own Sun.

Image: NASA/JPL-Caltech/2MASS/B. Whitney (SSI/University of Wisconsin).

The new images are permeated with a greenish mist that is rich in hydrogen and carbon compounds called polycyclic aromatic hydrocarbons (PAHs). PAHs are found on the Earth in sooty vehicle exhausts and on charred grills, but in space, they lurk in dark clouds that spawn stars. Of course they are not really green, the colour is added to bring out the glow that is only visible in infrared wavelengths. One particular snap shot (above) is defined by the streaks of dust grains across the star in the upper left, that are likely aligned with the magnetic field of the star. Around the star that lies in the centre of the image, GL 490, several dense clumps of gas have been identified; these give away the locations of the youngest large stars that will help astronomers learn more about the earliest stages of massive star formation.

Image: NASA/JPL-Caltech/2MASS/B. Whitney (SSI/University of Wisconsin).

In another image (above), an outflow of gas from a new star in a region known as IRAS 21078+5211 is seen ramming into the surrounding hydrogen gas to make it glow. The survey will help detail the structure of the outer Galaxy and try and determine where there Milky Way meets the void of intergalactic space.

GLIMPSE360 began last September and will continue through to the start of 2011, with data processing expected to take another year. Once the full survey is complete and combined with the previous GLIMPSE and GIMPSE3D data, it will provide a 360 degree field-of-view of the Galaxy, ranging in height from 2.7 degrees to 8.4 degrees at the centre.

"We look forward to what GLIMPSE360 will show us," Whitney says. "The adventure is just getting started."