A huge “superbubble” 1,000 light-years wide surrounds our planet. Today, astronomers have made the first-ever 3D map of its magnetic field.
The gigantic structure, known as a “local bubble”, is a hollow blob of hot, diffuse plasma enclosed in a shell of cold gas and dust on the surface of which stars are forming. This is just one of many hollows found in the Milky Way – making our galaxy look like a huge slice of Swiss cheese.
Superbubbles are shock waves from the agony of several massive stars, which in their final acts explode into huge supernovae that expel the gas and dust necessary for the birth of new stars. Over time, other stars, like ours, wander inside the cavities left by these explosions.
Related: Earth is at the center of a 1,000 light-year-wide ‘Swiss cheese’ bubble carved out by supernovae
Although they have a glimpse of how superbubbles form, astronomers still don’t know how these giant bubbles evolve through interaction with our galaxy. magnetic field, and how it affects the formation of stars and galaxies. To find out more, a team of astronomers, working as part of a summer research program at the Harvard-Smithsonian Center for Astrophysics, mapped the magnetic field of the local bubble.
“Space is full of these superbubbles that trigger the formation of new stars and planets and influence the overall shape of galaxies,” Theo O’Neillwho at the time was an undergraduate student studying astronomy, physics, and statistics at the University of Virginia, said in a press release. “By learning more about the exact mechanisms that drive the local bubble, in which the Sun lives today, we can learn more about the evolution and dynamics of superbubbles in general.”
The Milky Way, like many other galaxies, is filled with a magnetic field that gently steers stars, dust and gas into mind-bending structures such as gigantic bone-like filaments. Astronomers don’t know what gives rise to galactic magnetic fields. The Milky Way’s magnetic field, although considerably weaker than Earth, permeates our galaxy and its outer halo in depth, subtly influencing the formation of everything around it. However, since the strength of the magnetic field is weak compared to the force of gravity, and only acts on charged particles, astronomers have long omitted magnetism from their calculations. This makes short-term sense, but over vast cosmic timescales it could mean that their models are overlooking substantial effects.
“From a basic physics perspective, we’ve known for a long time that magnetic fields must play an important role in many astrophysical phenomena,” said Alyssa Goodman, an astronomer at Harvard University who was one of the research program mentors, in the release. “But studying these magnetic fields has been notoriously difficult. Today’s computer simulations and whole-sky surveys might finally be good enough to start to really incorporate magnetic fields into our larger picture of how the planet works.” the universe, from the movements of tiny specks of dust to the dynamics of clusters of galaxies.”
To plot the magnetic field map, the astronomers used earlier information from the European Space Agency’s (ESA) Gaia space telescope, which had inferred the approximate boundaries of the local bubble from concentrations of distant cosmic dust. With that in hand, the researchers turned to data from another ESA space telescope, Planck, which showed the faint microwave emissions of polarized light from the dust. As the polarization, or direction of vibration, of light is a key telltale of the magnetic field acting on the dust, astronomers used it to stitch the data points together into a vast 3D tapestry of the superbubble’s surface.
The researchers note that to make their map they made some big assumptions that they’ll need to test – including that polarized dust is on the bubble’s surface – but once they’ve refined its accuracy, they believe it will. could become an invaluable tool for studying star formation in our galactic backyard.
“With this map, we can really begin to probe the influences of magnetic fields on star formation in superbubbles,” Goodman said. “And moreover, to better understand how these fields influence many other cosmic phenomena.”