Astronomers have discovered a gigantic, undulating wave of dust and gas where newborn stars are forged over an 80 million billion kilometer stretch of the Milky Way.
The gaseous structure, which holds more mass than 3 million suns, runs directly behind our solar system as viewed from the heart of the galaxy, but has eluded observation until now.
The spectacular string of stellar nurseries forms the largest known wave in the Milky Way and was announced, appropriately, at a scientific conference near the surf mecca of Waikiki beach in Hawaii.
“It is the largest gaseous structure we know about in the Milky Way,” Harvard University professor of applied astronomy Alyssa Goodman said on Tuesday at an American Astronomical Society meeting in Honolulu. “It’s right up in our face. It’s crazy that it’s so close by.”
Measurements of the wave show that it stretches more than 9,000 light-years and makes up what is known as the “local arm” of the Milky Way.
Looking down on the flat disc of the galaxy, the wave appears as a straight line about 400 light-years wide, but from the side, it rises and falls 500 light-years above and below the plane of the galaxy.
For comparison, the width of the solar system is about half a light-day — the distance light travels in 12 hours.
The discovery has thrown up a raft of questions, not least around how the wave formed.
One idea is that a much smaller galaxy clattered into that part of the Milky Way in the past, setting off ripples that spread like those from a stone tossed into a pond. A more exotic hypothesis sees a role for the mysterious dark matter that lurks unseen in galaxies.
If the wave was set off by a cosmic collision, the ripples could pull the enormous dense clouds of dust and gas around for millions of years before finally settling down.
“We think the wave is dynamic, but the timescale of its motion up and down, we really don’t know,” Goodman said.
Astronomers discovered the cosmic wave while mapping the distribution of vast clouds of dust and gas that pepper our galactic neighborhood. Inside these dense clouds, gas can be compressed to such extremes that new stars are born.
Just as the sun reddens at sunset, so starlight reddens as it passes through interstellar dust. With this in mind, scientists analyzed the colors of stars whose distances had been measured with unprecedented accuracy by the European Space Agency’s Gaia spacecraft.
The dust reddens the light of stars behind it, but has no effect on those in front.
Writing in the journal Nature, the astronomers described how the map revealed the shape of the giant wave of connected clouds. While earlier studies had suggested a huge ring of stellar nurseries around the solar system known as Gould’s Belt, the new map shows there is no ring, but a massive wave instead.
The sun might have originated in what the scientists have called the Radcliffe Wave, after their home base, the Radcliffe Institute for Advanced Study.
According to their calculations, the sun now lies 500 light-years from the wave, but crossed it about 13 million years ago and might cross it again in another 13 million years.
“It’s been a puzzle for decades as to why so many of our local Gould’s Belt star-forming regions lie so far out of the galactic plane,” said Exeter University astrophysicist Jennifer Hatchell, who was not involved in the study. “The previous expanding-ring model fitted cloud positions and velocities well, but never entirely explained the fragmentary structure, rotation or the origin of the ring, which required the energetic equivalent of several supernovae.”
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