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Current Events: Image Release: Giant Magnetic Ropes in a Galaxy’s Halo

By Stacy Palen

A new composite image released by the National Radio Astronomy Observatory superimposes radio data on a visual image of a galaxy. Magnetic fields here are shown in blue and green, indicating alternate directions.

Here are some questions that you can ask your students based on this image:

1) What is the Hubble type of this galaxy?

Answer: A spiral.

2) How do you know?

Answer: Because there is a disk, viewed edge on.

3) What is the Hubble type of the large galaxy directly above the primary galaxy in this image?

Answer: Elliptical.

4) How do you know?

Answer: There is no disk.

5) The blue and green false color “hair” represents the magnetic fields of the galaxy. Blue indicates that the magnetic field points roughly away from us, while green points roughly toward us. These magnetic fields are described as “spiraling” and as “ropes.” Make a sketch of the magnetic field lines of the galaxy that fits these descriptions and observations.

Answer: This is a genuine question, not a test of their understanding. I am picturing a spiral for each blue/green pair that is roughly perpendicular to the disk. I wonder what students “get” from these descriptions?

6) Are the magnetic fields above the disk of the galaxy symmetric with those below the disk? What might cause this?

Answer: They are not. It could be because the magnetic field is being generated differently, or it could be because the observations are more resolved above the disk than below. That could happen if the galaxy disk was tilted so that the top of the disk is tilted toward us.

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