Interstellar cartographers have mapped for the first time in 3D the magnetic field trapped in the Local Bubble.
The local bubble is a cavity at least 1,000 light-years wide in the interstellar gas around the solar system—a “superbubble” in interstellar space. The local bubble was blown up by a series of supernovae between 10 and 20 million years ago and is one of many such bubbles in the interstellar medium that pierce our Milky Way galaxy and others like cavities in Swiss cheese.
“Compiling this 3D map of the Local Bubble will help us explore superbubbles in new ways,” said Theo O’Neill, who used data from the European Space Agency’s (ESA) Gaia and Planck missions to map. O’Neill was an undergraduate student at the University of Virginia when he mapped during a summer research camp at the Harvard-Smithsonian Center for Astrophysics under Harvard astrophysicist Alyssa Goodman.
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Artistic depiction of the surface of the Local Bubble where stars are born. (Image credit: Theo O’Neill/World Wide Telescope)
“We have known for a long time that magnetic fields must play an important role in many astrophysical phenomena,” Goodman said in a statement.
“But studying these magnetic fields has been extremely difficult,” she said. “Today’s computer simulations and all-sky surveys may be good enough to start really including magnetic fields in our larger picture of how the universe works, from the movement of tiny dust grains to the dynamics of galaxy clusters.”
The key to mapping the structure of the Local Bubble’s magnetic field is interstellar dust, especially charged particles that can follow magnetic field lines in space. In particular, the ESA Planck mission, which studied the cosmic microwave background radiation between 2009 and 2013, was also sensitive to the polarized microwave emission from this charged dust. Polarization refers to the orientation of the dust emitting microwaves; this orientation is influenced by the magnetic field lines. Meanwhile, observations by the ESA Gaia spacecraft, launched in 2013, have pinpointed the location of interstellar dust on the surface of the Local Bubble, which is expanding and sweeping up both dust and magnetic field lines scattered throughout space.
To start, O’Neill put together a 2D map of the magnetic fields in the sky before performing geometric analysis to turn it into a 3D representation. Goodman’s previous research showed that most young stars and star-forming regions near the Sun are on the edge of the expanding Local Bubble, where dust and gas are compressed. O’Neill’s map shows that the magnetic field lines do indeed line up with large star-forming regions on the surface of the Local Bubble, such as the Orion Molecular Cloud, which hosts the famous Orion Nebula, 1344 light-years from Earth. Earth.
However, there are some caveats that make the map look somewhat rough around the edges. “We made some big assumptions to create this first 3D magnetic field map; it’s by no means a perfect picture,” Goodman said.
There are two main assumptions: first, that the dust producing polarized radiation is on the surface of the Local Bubble, and not beyond, and second, that magnetic field lines are drawn to the edge of the Local Bubble as it expands. However, as computer simulations and scientists’ understanding of superbubbles improve, the accuracy of the map will also improve.
As with the Local Bubble, astronomers believe that superbubbles in general play a significant role in star formation.
“Space is full of these superbubbles that are causing new stars and planets to form and affecting the overall shape of galaxies,” O’Neill said. “By learning more about the exact mechanics that govern the local bubble that the sun lives in today, we can learn more about the evolution and dynamics of superbubbles in general.”
O’Neill presented the study at the 241st meeting of the American Astronomical Society, which will take place this week in Seattle and virtually.
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