In DepthAstronomy

Most distant Milky Way outpost mapped

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Science  13 Oct 2017:
Vol. 358, Issue 6360, pp. 160-161
DOI: 10.1126/science.358.6360.160

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It's hard to map the structure of the Milky Way from the vantage of the solar system, which sits in the disk of the galaxy, on a spur of one of its spiral arms. Clouds of gas and dust obscure the view, especially along sightlines through the galactic center. Now, astronomers are mapping the arms with the help of star-forming regions that contain clouds of water vapor, glowing brightly with radio waves that can penetrate the gas and dust. By measuring them, the observers have traced points throughout the arms, like lighthouses on a coastline, and helped confirm an emerging consensus that the galaxy has four spiral arms. Among the tracked water clouds is one 66,000 light-years away, the most distant outpost ever mapped, a result described this week in a study in Science.

  • * Joshua Sokol is a journalist in Boston.