A Magnetic Tunnel Surrounds the Earth

Imagine if your eyes could see radio waves!
We might be able, if we had the ability to see into space, to see a tunnel made of radio waves. It would measure approximately 1,000 light-years in length and be located about 350 light years away.

This tunnel explains the two brightest radio features visible in the sky.

In the 1960s, radio astronomy was just beginning when astronomers discovered the North Polar Spur as well as the Fan Region. The North Polar Spur, a huge ridge of hot gases that rises above he plane of the Milky Way, is massive. It emits radio waves and x-rays. There has been much debate about the nature of this object and its distance from Earth over the years since it was discovered. It could be related to the Fermi Bubbles, or an ancient supernovae blast. Astronomers believe it is.

One of the most prominent polarized radio features is the Fan Region. The nature of the Fan Region is also a matter of debate. Some argue that it's a local feature while others believe that it exists on a global scale.

The conventional view shows the Galaxy in radio waves. The Galactic centre is in the middle. Credit: Haslam et al. (1982) With annotations by J. West.

In a new paper, a team of Canadian and American researchers shows that the two features are linked. The paper's title is A Unified Model for The Fan Region and The North Polar Spur: A bundle of filaments within the Local Galaxy. It was written by Dr. Jennifer West, Research Associate at The Dunlap Institute for Astronomy and Astrophysics.

If we looked up into the sky, we'd see this tunnel-like structure almost everywhere we looked. That is, if our eyes could detect radio light.

According to the authors, both the Fan Region and the NPS are part of the same feature. The feature is composed of 1,000-light-year-long ropes that are made up charged particles and a magnetic force. They are right in front our eyes but we cannot see them. We would see the tunnel-like structure if we could look up into the sky, West explains.

The tunnel is at 30 GHz in this image taken from the study. The Fan Region is to the left and the North Polar Spur sweeps up. Image Credit: West et al., 2021.

In a press release, West explained that magnetic fields don't exist in isolation. It was difficult to determine how these two connected. West believes that her team was the first to join the pair.

West claims that she has been thinking about this pair of features since the first time she saw a radio map showing the sky. She has created a computer model of what the radio sky from Earth, which she altered to show the location and shape of the radio ropes. It was possible to create the radio structure around us thanks to the model. The model showed her how the sky would look through radio telescopes. She was able to see the model from a different perspective, which helped match the observed data.

The discovery was made possible by a 1965 paper.

Tom Landecker was one of our co-authors. He told me years ago about a 1965 paper that West had written. This paper was from the early days radio astronomy. Based on the limited data at the time, the authors (Mathewson & Milne) speculated that these polarized radio waves could have arisen from our view of the Local Arm of the Galaxy. This paper inspired me to create this model and tie it to the much better data our telescopes provide us today.

Astronomers often look at a map that shows the North pole of the Galaxy in the upper right and the Galactic center in the middle.

West compares their work to a map of Earth. The North Pole is at the top and the Equator is in middle. It can be drawn from another perspective though, as West's computer model enabled her to. She explains that most astronomers view a map that shows the Galactic centre at the center and the North pole of Galaxy in the upper left. This idea came from the need to remake the map at a different point in its middle.

Left: The sky as seen in radio polarized waveforms. The Van-Gogh-like lines indicate the direction of the magnetic field. These radio data are projected in the same way as they would appear in the sky, with constellation names and outline of the brightest stars. Credit: Dominion Radio Astrophysical Observatory/Villa Elisa telescope/ESA/Planck Collaboration/Stellarium/J. West. Right: The sky as seen through our eyes in its original projection and orientation. These are the same constellations and brightest stars as in the previous photo. Credit: Stellarium/J. West.

This is a very clever piece.

This is a very clever piece of work, according to Dr. Bryan Gaensler (a professor at Dunlap Institute) and the author of the publication. Jennifer pitched it to me at first, and I was skeptical that there would be any explanation. She was able to convince my! I am eager to see what the rest of the Astronomy Community thinks.

West is an expert on galaxies as well as the ISM. She is looking forward to further research that will hopefully reveal how the various magnetic structures in our sky are connected.

She explains that magnetic fields cannot exist in isolation. All of them must be connected to one another. The next step is to understand how the local magnetic field links to both the larger-scale Galactic magnetic fields and to the smaller-scale magnetic fields of the Sun and Earth.

The study illustrates the arrangement of loops made on nested cylindricals. Although the diagram is not scaled, the arrangement of the filaments in the diagram is correct relative to their positions and relative to one another. Image Credit: West et al. 2021

These structures are not visible to the naked eye. However, knowing that they exist is thought-expanding.

It's amazing to think that these structures can be seen when we look up at the night sky, stated West.

Astronomers have debated for years about the nature of North Polar Spur. There have been contradictions in different research. Some studies prove it is distant, while others make it more local. These contradictions were resolved by West and her coauthors. This model is consistent with the many observational studies of these regions. It is also able to resolve an apparent contradiction found in the literature, which suggests that the NPS's high latitude portion is closer than the lower latitude ones.

The authors state that this model can be used to develop a holistic model for the magnetic fields in galaxies. We don't know enough about the evolution and origin of regular magnetic fields in galaxies, nor how they are maintained.

The model doesn't match observations perfectly. The model and data are not perfect matches. The NPS ends are the most affected by the disagreement. They believe that depolarization is caused by some foreground structure and that the model generally agrees with the data. Image Credit: West et al. 2021

The team hopes that a better understanding and appreciation of features such as the tunnel will allow for a greater understanding of other distant magnetic features. There are also super-bubbles and filaments that are much larger than those shown. They have been observed by astronomers in distant regions of Milky Way.

It is not easy to study these distant features. The team concludes that it is unlikely that we have the resolution or sensitivity required to see this level structure in other locations than the local environment, and possibly in Perseus' arm.

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