A 3D Magnetic Map of the Local Bubble

Long ago, supernovae blew out a gigantic bubble, sweeping up interstellar gas into what is now a 1,000 light-year-wide shell. The Sun, purely by chance, sits near its center. A new map of the magnetic field along this shell may help astronomers understand the origin of this Local Bubble as well as the role of such structures in galaxy evolution.

Last year, Catherine Zucker (Center of Astrophysics, Harvard & Smithsonian) announced at the 240th meeting of the American Astronomical Society (AAS) that she and colleagues had mapped the dust of the Local Bubble by measuring its dimming effect on more distant stars. The bubble, she found, had pushed out gas, triggering starbirth in nurseries all around the Sun.

One year later, at the AAS's 241st meeting in Seattle, Theo O'Neill (University of Virginia) reported work done with members of the same team to add magnetic field information to that map. O'Neill used the European Space Agency's Planck satellite to look at polarized light, in which light waves became aligned after scattering off intervening dust. By assuming that the dust lies in the Sun's vicinity rather than farther away in our galaxy or beyond, O'Neill was able to transform the polarization of light into magnetic field strength and direction.

The result is a magnetic map of the Local Bubble; you can interact with a 3D version here. The study itself is available on Authorea but has not yet undergone peer review.

Mapping the magnetic field is only the first step for further understanding the Local Bubble and others like it across the galaxy. "There have been recent results finding hundreds to thousands of bubbles in single galaxies," O'Neill says. "It's likely that our own Milky Way is similar."

While bubbles are probably ubiquitous in the Milky Way, it's harder to see detail in the ones beyond the local one that surrounds us. Yet they impact the galaxy's evolution in subtle ways. The sweeping-out of gas deprives the central regions of star-forming fuel while at the same time triggering starbirth along the shell. Bubbles may thus regulate the rate at which stars are born, shape the magnetic field that permeates the galactic disk, and even collide with one another.

Ultimately, the magnetic map can also help us understand how the Local Bubble came to be. "There may be insights from this present-day map, and extrapolating back into time," O'Neill says, adding that that extrapolation could be extended as far back as the chain of supernovae that blew out the Local Bubble in the first place.

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