Astronomers at the Astrophysics Center | Harvard and the Smithsonian (CfA) have unveiled a first-of-its-kind map that could help answer decades-old questions about the origins of stars and the influences of magnetic fields in the cosmos.
The map reveals the likely structure of the magnetic field of the Local Bubble – a gigantic 1,000 light-years deep in space that surrounds our Sun. Like a piece of Swiss cheese, our galaxy is full of these so-called superbubbles. The explosive supernova death of massive stars blows these bubbles away, and in the process concentrates gas and dust—the fuel for producing new stars—on the outer surfaces of the bubbles. These thick surfaces consequently serve as rich sites for further star and planet formation.
However, scientists’ overall understanding of superbubbles remains incomplete. With the new 3D magnetic field map, researchers now have new information that could better explain the evolution of superbubbles, their effects on star formation and galaxies in general.
“Assembling this 3D map of the local bubble will help us examine superbubbles in new ways,” says Theo O’Neill, who led the mapping effort during a 10-week NSF-sponsored summer research experience at CfA, while still an undergraduate. at the University of Virginia (UVA).
“Space is full of these superbubbles that trigger the formation of new stars and planets and influence the overall shapes of galaxies,” continues O’Neill, who will graduate from UVA in December 2022 with a degree in astronomy-physics and statistics. “By learning more about the exact mechanics that drive the local bubble that the Sun lives in today, we can learn more about the evolution and dynamics of superbubbles in general.”
Along with colleagues, O’Neill presented the findings at the 241st annual meeting of the American Astronomical Society on Wednesday, January 11, in Seattle, Washington. Interactive 3D figures and a pre-print of the research are currently available on Authorea. The research was conducted at CfA under the guidance of Harvard professor and CfA astronomer Alyssa Goodman, in collaboration with Harvard PhD student Catherine Zucker. graduate student in astronomy, Jesse Han, Harvard Ph.D. student and Juan Soler, a magnetic field expert in Rome.
“From the point of view of basic physics, we have long known that magnetic fields must play an important role in many astrophysical phenomena,” says Goodman, who wrote his Ph.D. thesis on the importance of cosmic magnetic fields thirty years ago. “But studying these magnetic fields has been notoriously difficult. The difficulty permanently draws me away from magnetic field work, but then new observational instruments, computational methods, and enthusiastic colleagues tempt me back. good enough to really begin to incorporate magnetic fields into our larger picture of how the universe works, from the motions of tiny dust grains to the dynamics of galaxy clusters.”
The local bubble has emerged as a hot topic in astrophysics by virtue of being the superbubble in which the Sun and our Solar System now reside. In 2020, the 3D geometry of the local bubble was originally developed by researchers in Greece and France. Then in 2021, Zucker, now of the Space Telescope Science Institute, Goodman, João Alves of the University of Vienna, and their team showed that the surface of the local bubble is the source of all nearby young stars.
These studies, along with the new 3D magnetic field map, were based in part on data from Gaia, a space observatory launched by the European Space Agency (ESA). While measuring the positions and motions of stars, Gaia was also used to infer the location of cosmic dust, recording local concentrations and showing the approximate boundaries of the local bubble.
These data were combined by O’Neill and colleagues with data from Planck, another ESA-run space telescope. Planck, which surveyed the entire sky from 2009 to 2013, was designed primarily to observe the light left over from the Big Bang. In the process, the spacecraft compiled measurements of microwave-wavelength light from across the sky. The researchers used some of the Planck observations tracking the relevant Milky Way dust emissions to help map the local bubble’s magnetic field.
Specifically, the observations of interest consisted of polarized light, that is, light that vibrates in a preferred direction. This polarization is produced by magnetically aligned dust particles in space. Dust alignment, in turn, speaks of the orientation of the magnetic field acting on the dust particles.
Mapping the magnetic field lines in this way allowed researchers working on the Planck data to compile a 2D map of the magnetic field projected across the sky as seen from Earth. To transform or “de-project” this map into three spatial dimensions, the researchers made two key assumptions: first, that most of the interstellar dust producing the observed polarization is on the surface of the local bubble. And second, that the theories predicting that the magnetic field would be “swept” into the surface of the bubble as it expands are correct.
Later, O’Neill performed the complicated geometric analysis required to create the 3D magnetic field map during the CfA summer internship.
Goodman likens the research team to the pioneering cartographers who created some of the first maps of the Earth.
“We made some big assumptions to create this first 3D map of a magnetic field; it’s by no means a perfect picture,” she says. “As our technology and physical understanding improves, we’ll be able to improve the accuracy of our map and hopefully confirm what we’re seeing.”
The 3D view of the emerging magnetic spirals represents the structure of the superbubble’s magnetic field in our neighborhood, if the field has indeed been swept into the surface of the bubble and if most of the polarization is produced there.
The research team further compared the resulting map to features along the surface of the local bubble. Examples included the Per-Tau Shell, a giant spherical star-forming region, and the Orion Molecular Cloud Complex, another prominent stellar nursery. Future studies will examine the associations between magnetic fields and these and other surface features.
“With this map, we can really begin to probe the influences of magnetic fields on star formation in superbubbles,” says Goodman. “And for that matter, you better understand how these fields influence many other cosmic phenomena.”
Because magnetic fields only affect the motion and orientation of charged particles in astrophysical environments, Goodman says there has been a tendency to set aside the influence of fields when building simulations and theories in which gravity—which acts on all matter—is the primary force at play. . Further discouraging its inclusion, magnetism can be a fiendishly complex force to model.
This omission of the influence of magnetic fields, while understandable, often misses a key factor that controls the motions of gases in the universe. These motions include gas flowing onto stars as they form and flowing away from stars in powerful jets emanating from them as they gather matter into a planet-forming disc. Even though the effect of magnetic fields is tiny from moment to moment in the low-density environments where stars form, given the millions of years of time it takes to gather gas and turn it into stars, the magnetic effects can add up plausibly. to something substantial in time.
Goodman, O’Neill and their colleagues look forward to finding out.
“I had a great experience doing this research at CfA and putting together something new and exciting with this 3D magnetic map,” says O’Neill. “I hope this map is a starting point for expanding our understanding of superbubbles throughout the galaxy.”
Provided by the Harvard-Smithsonian Center for Astrophysics
Citation: Cosmic superbubble magnetic field imaged in 3D for the first time (2023 January 11) Retrieved January 12, 2023 from https://phys.org/news/2023-01-cosmic-superbubble-magnetic-field-3d .html
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