There are chunks and lumps that don’t look like anything,” explained Peek. “We don’t have long, skinny spiral arms after all, at least in this section of the galaxy. They found that many of the clouds do not, in fact, lie at the distance of the Perseus arm, but instead stretch along a distance of some 10,000 light-years. They compared the distances measured via dust reddening to those determined by the velocity relationship. Peek and his team examined a region of space known as the Perseus spiral arm, which is beyond our Sun in the Milky Way’s disk. The more dust that is between the star and our telescope, the redder the star will appear compared to its natural color. 3D dust maps can be created by examining the colors of large collections of stars spread across the sky. In general within our galaxy, gas and dust are closely associated, so if you can map one, you also map the other. To investigate this question, Peek and his colleagues examined not the gas, but the dust. Can those extra motions throw off our maps? Chunky and Lumpy The question then becomes, what about a non-ideal situation? While the motion of any given gas cloud might be dominated by its rotation around the galactic center, it undoubtedly has some additional, more random motions as well. 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. As a result, the Perseus arm may be much clumpier and less well-defined (lower right), Distances are Key New measurements (middle right) show that some of these dust clouds are much closer or farther from the Sun than originally thought. At upper right, a shaded region shows the previously believed shape of the Perseus arm, demarcated by a combination of masers and dust clouds. Astronomers created this map by measuring the locations of natural radio sources known as masers (pink dots in pullouts at right) and dust clouds (blue dots). In a map of the Milky Way, the neighboring spiral arm just beyond the Sun is known as the Perseus arm. Figure 1: The illusion of a continuous Perseus Arm. We don’t see evidence that pieces we’ve been connecting up are actually connected.” “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? 1) 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. The illusion is a result of complexities first predicted by W. However new research shows that at least a portion of the Perseus arm may be illusory, without any well-defined structure. Previous work suggested that the Perseus arm possesses a narrow and distinct shape. Moving outward from Earth’s location, astronomers have constructed a model of the neighboring spiral arm, known as the Perseus arm. But what shape, exactly, would those spiral arms have? Stuck here with no bird’s-eye view, we have to apply other methods to measure the galaxy’s shape. If we could travel faster than light and climb above the plane of our galaxy, we would see a flat disk with spiral arms wrapping around the core. That band is our Milky Way galaxy, which we see edge-on since we’re inside of it. December 16, 2021: When you go outside at night in a rural location with dark skies, you can look up and see a band of stars crossing the sky.Astronomy and Telescopes Hubble Status and Imagery in the Period 2021
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