Mapping the Milky Way from the inside out

NASA scientists describe the task of mapping our own Milky Way galaxy as like trying to create a map of your house while confined to only the living room.

“You might peek through the doors into other rooms or look for light spilling in through the windows. But, in the end, the walls and lack of visibility would largely prevent you from seeing the big picture.”

The planet Earth is situated about two-thirds of the way out from the galaxy’s centre. Clouds of dust block our view of many of the galaxy’s stars – and the mapping work is far from complete but NASA reports that researchers have been helped by a new method that takes advantage of data from NASA’s Wide-field Infrared Survey Explorer, or WISE.

Using WISE, the research team has discovered more than 400 dust-shrouded nurseries of stars, which trace the shape of our galaxy’s spiral arms. Seven of these “embedded star clusters” are described in a new study published online in the Monthly Notices of the Royal Astronomical Society.

“The sun’s location within the dust-obscured galactic disk is a complicating factor to observe the galactic structure,” said Denilso Camargo, lead author of the paper from the Federal University of Rio Grande do Sul in Brazil.

The results support the four-arm model of our galaxy’s spiral structure, with the arms are where most stars in the galaxy are born.

They are stuffed with gas and dust, the ingredients of stars. Two of the arms, called Perseus and Scutum-Centaurus, seem to be more prominent and jam-packed with stars, while the Sagittarius and Outer arms have as much gas as the other two arms but not as many stars.

The new WISE study finds embedded star clusters in the Perseus, Sagittarius, and Outer arms. Data from the Two Micron All Sky Survey (2MASS), a ground-based predecessor of WISE from NASA, the National Science Foundation and the University of Massachusetts, Amherst, helped narrow down the distances to the clusters and pinpoint their location.

Embedded star clusters are a powerful tool for visualizing the whereabouts of spiral arms because the clusters are young, and their stars haven’t yet drifted away and out of the arms. Stars begin their lives in the dense, gas-rich neighborhoods of spiral arms, but they migrate away over time. These embedded star clusters complement other techniques for mapping our galaxy, such as those used by radio telescopes, which detect the dense gas clouds in spiral arms.

“Spiral arms are like traffic jams in that the gas and stars crowd together and move more slowly in the arms. As material passes through the dense spiral arms, it is compressed and this triggers more star formation,” said Camargo.