As a result, by measuring gas velocities, we can determine distances and hence the underlying structure of the galaxy. In an ideal situation, the line-of-sight motion we measure for a gas cloud is directly related to its distance due to the overall rotation of the Milky Way. To fill those gaps, astronomers switch from examining star-forming regions to gas clouds, and more specifically, the motions of those gas clouds. However, this technique inevitably leaves gaps. The gold standard is to use parallax measurements of naturally occurring radio sources called masers, some of which are found in high-mass star-forming regions. When mapping our galaxy, the biggest challenge is finding the distance to any given star, star cluster, or gas clump. We don’t see evidence that pieces we’ve been connecting up are actually connected.” Distances are Key “This work calls that picture into question. “We have long had a picture of the galaxy in our minds, based on a combination of measurements and inference,” said Josh Peek of the Space Telescope Science Institute (STScI) in Baltimore, Maryland. However, new research finds that at least one portion of the outer Milky Way (beyond the Sun’s location) is much more clumpy and chaotic. Previous work has suggested that the Milky Way is what’s known as a “grand design” spiral, with long, narrow, well-defined spiral arms. As the old saying goes, you can’t see the forest for the trees, and if you’re in the middle of the forest, how can you map its groves without a bird’s-eye view? For decades, astronomers have struggled to map the Milky Way’s disk and its associated spiral arms. Our Milky Way has long been known to be a spiral galaxy, shaped much like a fried egg with a bulbous central bulge and a thin, flat disk of stars.
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