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Now it turns out that the Radcliffe Wave is actually waving. This is stated by a paper published Tuesday in the journal Nature.
Star-forming clouds rise high above the plane of the galaxy and then fall back down. This type of oscillation is known as a traveling wave, which is similar to sports fans “doing the wave” by getting up from their seats in a synchronized pattern around the stadium.
“This wave issue (you can find articles hinting at it in the past) but it’s already resolved. This is a brick in the wall and it’s not coming out,” said Bob Benjamin, an astronomer at the University of Wisconsin in Whitewater who was not part of this new research. “This latest paper is a really important step in understanding the origin of this structure.”
This structure is inside our galaxy and practically next to it. It’s a short distance away, if you could span 500 light years.
The story has another twist: it seems that our solar system passed through the Radcliffe wave about 13 million years ago. And that could have been an interesting time for life on Earth. These star-forming regions have more than their fair share of exploding stars.
“Thirteen million years ago, we think we might have gone through a supernova festival,” said study co-author Catherine Zucker, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics.
Until just a few years ago, no one recognized that the numerous star-forming clouds relatively close to the Sun were part of a coherent structure. This is because astronomers can see distant galaxies better than the one around us, the Milky Way. There is no telescope in intergalactic space, a couple of million light years away, that allows us to obtain beautiful images of our entire galaxy. (If there is, it’s not one of ours.)
“It’s really hard to see what the structure of your hand is if you put it too close to your face,” explains Alyssa Goodman, a professor of astronomy at Harvard and co-author of the new report. “We can’t fly out of the galaxy.”
Astronomers have known for a century that the Milky Way is just one of many galaxies. They also know that ours is a large spiral galaxy very similar to the neighboring Andromeda galaxy.
The cloud-like ribbon of milky light that can be seen on a clear night, and which, as Galileo discovered four centuries ago with a telescope, is filled with individual stars, is an edge-on view of the plane of our galaxy. The galaxy is a pancake-shaped disk, made of relatively thick dough, so to speak. We are there in the mix and we can see stars in all directions that are part of the pancake.
But only in recent years has it been possible to create an accurate three-dimensional map of the stars and gas in our sector of the galaxy. This is due in part to the European Space Agency’s Gaia spacecraft, which is designed to measure with unprecedented precision the distances to millions of stars in our galaxy and their motion relative to each other.
“Fixed stars,” as astronomers and sailors call them, are actually not just sitting in deep space. Everything is moving. Our solar system orbits the center of the galaxy over the course of about 226 million Earth years.
Using data from Gaia, Joao Alves, Zucker, Goodman and six colleagues described the Radcliffe wave in a document from 2020 in nature. They named it after early 20th-century female astronomers associated with Radcliffe College, including Radcliffe graduate Henrietta Leavitt, who discovered that the periodic brightness of certain stars encoded information about their distance from Earth.
That breakthrough was instrumental in the discovery that the intriguing “spiral nebulae” seen through telescopes are actually structures outside the Milky Way: distinct galaxies in a universe even vaster than previously imagined.
The Radcliffe Wave appears to be the backbone (or “gas tank”, as a 2022 article put it) of the spiral arm of our galaxy closest to our sun, known as the Orion Arm or Local Arm. Additional updates to Gaia allowed scientists to create theoretical models to track the movement of star clusters within the wave, revealing their undulations.
The big question now: Why does the Radcliffe wave wave?
“Who ordered that?” Goodman asked.
Clearly something happened to disrupt our galactic neighborhood and impose disorder on the heavens. One possibility is that something, perhaps a dwarf galaxy, crashed into the Milky Way and caused a huge splash, and the ripple was a domino effect.
Another possibility is that a sequence of supernovae (explosions of stars that emit powerful bursts of radiation) shook things up. Or it could be a combination of factors.
“It could be that the stars exploded as supernovae and expelled gas and dust from the galactic plane,” said Ralf Konietzka, a doctoral candidate at Harvard and lead author of the new paper. This wave pattern will disappear in a few tens of millions of years, he said.
The journey of the Earth through the wave.
There is more research to be done here, Zucker and his colleagues say, and more scientific papers are on the horizon. There could be signs in the geological record that the Earth was affected by supernova explosions in that distant transit through the Radcliffe wave.
The Earth has a magnetic field that helps protect it from potentially harmful radiation from the sun. And the sun’s solar wind creates a large protective bubble around the entire solar system that helps protect us from dangerous particles traveling through space from other points in the galaxy.
But this is where “interstellar climate” complicates the picture. A nearby supernova could have compressed that bubble, called the heliosphere, to the point that our planet was completely exposed to the interstellar medium.
The next step is to examine the geological record for signs that Earth was blasted with an iron isotope consistent with supernova exposure about 13 million years ago. And then compare that to anything interesting in the biological record.
“Galaxies may be even more dynamic than we previously thought,” Konietzka said.