ARTICLE:
A team of astronomers has found that the spiral arms of the Milky Way galaxy may stretch further into space than scientists previously believed. The discovery came from a method that bypasses one of the oldest problems in studying the galaxy: Earth is located inside one of the arms, making it difficult to map from within.
According to Fox News, the scientists made precise distance measurements of dust clouds in the spiral arms using data from two orbiting telescopes, NASA's Chandra, the most powerful X-ray telescope ever built, and the European Space Agency's XMM-Newton.
The team took advantage of rare, powerful gamma-ray bursts in distant galaxies. As X-rays from those bursts traveled through the Milky Way, some of the light bounced off dust clouds and created rings that could be measured with unusual precision.
"This is a very direct way — relying only on geometry — to precisely measure distances to the Milky Way's spiral arms," said Beatrice Vaia, the Italian PhD student who led the study. "Most other methods rely on assumptions about how the Milky Way rotates, which become increasingly uncertain in the outer regions of our galaxy."
The dust cloud in the most distant arm of the Milky Way was estimated to be about 3,500 light-years wide. Astronomers have been aware of the Milky Way's arms for at least a century, but mapping them has always been difficult given Earth's position inside one of them.
The implications of even small revisions to these measurements could be significant. "The differences are small, but any revision of these distances is important because they are so fundamental for understanding our galaxy," said Ilaria Fornasiero, a PhD student and co-author on the study. "For example, this could mean that astronomers have to revise estimates of the mass of the galaxy, because that affects how wide the arms stretch."
The technique has one significant limitation. Suitable gamma-ray bursts are extremely rare. Researchers found only a handful over the past 25 years that were bright enough and positioned correctly to allow measurement of the spiral arms.
"We will continue to be on the lookout for more," said co-author Andrea Tiengo.
