What if our eyes could see radio waves?
If we could, we might be able to look up into the sky and see a tunnel of rope-like filaments made of radio waves. The structure would be about 1,000 light-years long and would be about 350 light-years away.
This tunnel explains two of the brightest radio features in the sky.
Astronomers discovered the North Polar Spur and the Fan Region in the 1960s when radio astronomy was getting going. The North Polar Spur is a massive ridge of hot gas that rises above the plane of the Milky Way. It emits x-rays and radio waves. Over the decades since its discovery, there’s been an ongoing discussion about what it actually is and how far away it is. Astronomers thought it could be related to the Fermi Bubbles or a feature carved out by ancient supernovae explosions.
The Fan Region is one of the most dominant polarized radio features in the sky. There’s debate about the nature of the Fan Region, too, with some saying it’s a local feature and some arguing that it’s on a galactic scale.
The Galaxy is seen in radio waves in the conventional view with the Galactic centre in the middle of the image. Credit: Haslam et al. (1982) with annotations by J. West.
A team of researchers from Canada and the US presents evidence in a new paper showing that the pair of features are connected. The paper’s title is “A Unified Model for the Fan Region and the North Polar Spur: A bundle of filaments in the Local Galaxy.” The lead author is Dr. Jennifer West, Research Associate at the Dunlap Institute for Astronomy and Astrophysics at the University of Toronto.
“If we were to look up in the sky, we would see this tunnel-like structure in just about every direction we looked – that is, if we had eyes that could see radio light.”
Dr. Jennifer West, Dunlap Institute for Astronomy
The authors say that both the NPS and the Fan Region are parts of the same feature. The feature is made up of 1,000 light-years long “ropes,” which themselves are made up of charged particles and a magnetic field. They’re right in front of our eyes, but we can’t see them. “If we were to look up in the sky,” explains West, “we would see this tunnel-like structure in just about every direction we looked – that is, if we had eyes that could see radio light.”
This image from the study shows the tunnel at 30 GHz. The North Polar Spur sweeps up and to the right, while the Fan Region is on the left. Image Credit: West et al., 2021.
“Magnetic fields don’t exist in isolation,” West explains in a press release. The trick was to figure out how these two were connected. West thinks that her team is the first group of astronomers to join the pair of features.
West says she’s been thinking about the pair of features for 15 years since she first saw a radio map of the sky. In recent years she’s built a computer model that shows what the radio sky would look like from Earth as she changed the shape and location of the long radio ropes. The model made it possible to “build” the radio structure around us. It showed her what the sky would look like through radio telescopes. The model gave her a new perspective that helped her match the data to the observed data.
A paper from 1965 played a role in the discovery.
“A few years ago, one
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