The Milky Way's spiral arm that's home to our Solar System has been found to cradle the largest gaseous structure in the galaxy – a long, thin strip of jumbled star-forming matter measuring 9,000 light-years long and 400 light-years wide.
A team of researchers published details of their discovery in Nature this week. Named the Radcliffe Wave, after the Radcliffe Institute for Advanced Study at Harvard University, where the study was led, the structure had never been observed before and overturns 150 years of cosmological theory.
“No astronomer expected that we live next to a giant, wave-like collection of gas - or that it forms the local arm of the Milky Way,” said Alyssa Goodman, co-author of the paper and professor of applied astronomy at America's Harvard University.
Although the structure is giant - taking up nearly all of the space in what is known as the Orion Arm, or Local Arm, of the Milky Way - it was difficult to find. Scientists only spotted the giant thread of gas after mapping the smattering of young stars being born within that area when they analysed the data recorded by the European Space Agency’s Gaia spacecraft, which launched in 2013.
“Only within the last year or two have we obtained super accurate distance to these stellar nurseries, enabled by novel statistical analyses of Gaia data. It is not possible to see this structure on the sky,” Catherine Zucker, co-author of the paper and a graduate student at the Harvard Smithsonian Center for Astrophysics, told The Register.
Instead, the researchers combined 2D snapshots of different patches of the sky in order to piece together a 3D map of the interstellar matter in the Milky Way. Only then did the structure emerge, she explained.
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“It has transformed our understanding of the Local Arm of our galaxy, which is the arm closest to our Sun. Previous models of the arm model it as a spiral shape which lies in the disk of the galaxy,” Zucker added. The new study shows that the Local Arm is actually the Radcliffe Wave itself.
As the Sun travels along its galactic orbit around the Milky Way, it crosses in and out of the Radcliffe Wave, a motion the researchers have described as “surfing”.
“It appears that the Sun, on its galactic orbit, crossed the Radcliffe Wave 13 million years ago, and may cross it again in the future. So in a way we are 'surfing' the wave,” said Zucker.
She estimates that about one per cent of the total gas mass, about three million solar masses, has been used to form the tens of thousands of new stars across the Radcliffe Wave. The researchers are unsure how the structure formed itself, whether the Milky Way contains more of these colossal gas structures, and how it might impact star formation over time, but research is ongoing. ®