When discussing magnetic fields, images of the sun’s coronal loops or simulations of Earth’s magnetosphere may come to mind. But now, astronomers have observed the effects of a supersized magnetic field extending tens of thousands of light-years inside the two huge gamma-ray ‘bubbles’ that were discovered projecting from the top and bottom of the Milky Way two years ago.
The gamma-ray bubbles, detected by astrophysicists using data from the Fermi Gamma-ray Space Telescope, extend 50,000 light-years from the top and bottom of our galaxy’s disk. This discovery was amazing unto itself, but now astronomers of the Harvard-Smithsonian Center for Astrophysics (CfA) have detected strong, polarized radio emissions from the same regions.
But what does this mean?
In the presence of strong magnetic fields, radio waves can become polarized — a similar effect caused by polarized glasses when viewing visible light. This polarized radio emission is therefore evidence for the vast magnetic field that accompanies the gamma-ray bubbles.
According to the researchers, these magnetic lobes originate not from our galaxy’s central supermassive black hole (Sagittarius A*), but from intense star formation activity in a zone around the Milky Way’s nucleus measuring approximately 650 light-years wide. Amazingly, there appears to be small-scale structures — ridges — in the extended magnetic field, indicative of several episodes of intense star formation activity over the last 10 million years. The ridges are mapped in the image above.
These ridges are analogous to tree rings that exhibit seasonal changes and periods of climatic change — the ridges in the magnetic field lobes are likely periods of strong star formation.
Image: A false-color image of our Milky Way as seen in a projection that shows the galactic center at the center of the image, the plane of the galaxy stretching across the central band, and the two arc-shaped radio lobes of emission seen extending north and south of the plane. Several of the newly discovered magnetic structures are labeled. Credit: Carretti et al., and Nature