HONOLULU — The Earth and sun are right next to a wavy rope of star-forming gas, but astronomers only just noticed it.
Many of the most well-known nearby stellar nurseries — places like the Orion Nebula — are actually strung along a continuous thread of gas that stretches roughly 9,000 light-years, researchers report. The thread resembles a sine wave, soaring above and below the disk of the galaxy by about 500 light-years, and at one point, coming within 1,000 light-years of our solar system.
“Perhaps the oddest feature is how close it is to the sun, and we didn’t know about it before,” said Alyssa Goodman, a Harvard University astrophysicist who presented the results January 7 during a news conference at a meeting of the American Astronomical Society. The study was also published the same day in Nature.
The team dubbed the newly found structure the Radcliffe Wave, Goodman said, in honor of both the institute where much of the work was done and early 20th century female astronomers from Radcliffe College, a female liberal arts school that eventually became part of Harvard University.
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Despite its proximity to us, astronomers noticed the wave only now because of recent advances in the ability to pinpoint distances to known star-forming gas clouds. To nail down those distances, Goodman and colleagues looked at stars behind the clouds and deduced how dust within those clouds altered the colors of the stars. Combining those measurements with distances to those stars, provided by the European Space Agency’s Gaia satellite (SN: 4/25/18), allowed the team to map out the 3-D locations of the clouds with newfound precision, revealing that they line up along the wave.
“These kinds of waves have been seen in external galaxies,” says Lynn Matthews, an astrophysicist at the MIT Haystack Observatory in Westford, Mass., who was not involved with this study. “This gives us an opportunity to tie together phenomena that have been observed in several galaxies, and develop a unifying picture of what might cause these sorts of features.”
One immediate implication of the study is that a structure known as Gould’s Belt, thought since 1879 to be a nearby ring of stars and gas whose origin has long been debated, never existed. Turns out, the ring was just an illusion, a 2-D projection of this wave onto the sky.
“It’s a very careful study,” says Jay Lockman, an astrophysicist at Green Bank Observatory in West Virginia who was not involved with this research. “What’s interesting about this one is it ties together a lot of very familiar things in the sky that previously had a very different model.”
How the wave formed, and what it means for understanding the Milky Way, are both open questions. “It could have been from a collision, something falling down on the Milky Way,” Goodman said. Though Matthews, who along with her colleagues saw something similar in a spiral galaxy dubbed IC 2233, thinks such gas waves might arise from gravitational disturbances from various interacting components of the galaxy itself.
“The main point is it’s something internal to the galaxy, as opposed to needing to invoke the accretion of a dwarf galaxy or some cloud onto the disk,” Matthews says.
Regardless of how the wave formed, tracing the motion of the sun through space backward in time reveals that our solar system passed right through the Radcliffe Wave roughly 13 million years ago, possibly creating a spectacular nighttime vista. “It would have been great,” she said. “All these beautiful nebulae … would have been a lot closer and a lot easier to see and possibly all around us.”