“Astronomers have charted the magnetic field of the Local Bubble using data obtained by Planck and Gaia. Here, the short pink and purple vector lines on the surface of the bubble represent the orientation of the magnetic field discovered”

Cosmic superbubble’s magnetic field charted in 3D for the first time
by Harvard-Smithsonian Center for Astrophysics / January 11, 2023

“Astronomers at the Center for Astrophysics | Harvard & 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 magnetic field structure of the Local Bubble—a giant, 1,000-light-year-wide hollow in space surrounding our Sun. Like a hunk of Swiss cheese, our galaxy is full of these so-called superbubbles.

The explosive supernova deaths of massive stars blow up these bubbles, and in the process, concentrate gas and dust—the fuel for making new stars — on the bubbles’ outer surfaces. These thick surfaces accordingly serve as rich sites for subsequent star and planet formation. Scientists’ overall understanding of superbubbles, however, remains incomplete. With the new 3D magnetic field map, researchers now have novel information that could better explain the evolution of superbubbles, their effects on star formation and on galaxies writ large. “Putting together this 3D map of the Local Bubble will help us examine superbubbles in new ways,” says Theo O’Neill, who led the mapmaking effort during a 10-week, NSF-sponsored summer research experience at the 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 graduated 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, in which the Sun lives today, we can learn more about the evolution and dynamics of superbubbles in general.” Along with colleagues, O’Neill presented the findings at the American Astronomical Society’s 241st annual meeting on Wednesday, Jan. 11, in Seattle, Washington. 3D interactive figures and a pre-print of the research are currently available on Authorea . The research was conducted at CfA under the mentorship of Harvard professor and CfA astronomer Alyssa Goodman, in collaboration with Catherine Zucker, a Harvard Ph.D. astronomy alumna, Jesse Han, a Harvard Ph.D. student and Juan Soler, a magnetic field expert in Rome.

“From a basic physics standpoint, we’ve long known that magnetic fields must play important roles in many astrophysical phenomena,” says Goodman, who wrote her Ph.D. thesis on the importance of cosmic magnetic fields thirty years ago. “But studying these magnetic fields has been notoriously difficult. The difficulty perpetually drives me away from magnetic field work, but then new observational tools, computational methods and enthusiastic colleagues tempt me back in. Today’s computer simulations and all-sky surveys may just finally be good enough to start really incorporating magnetic fields into our broader picture of how the universe works, from the motions of tiny dust grains on up 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 find themselves. In 2020, the Local Bubble’s 3D geometry was initially worked out by researchers based in Greece and France. Then in 2021, Zucker, now of Space Telescope Science Institute, Goodman, João Alves of the University of Vienna, and their team showed that the Local Bubble’s surface is the source of all nearby, young stars. Those studies, along with the new 3D magnetic field map, have relied on data in part from Gaia, a space-based observatory launched by the European Space Agency (ESA).

While measuring the positions and motions of stars, Gaia was used to infer the location of cosmic dust as well, charting its 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-led space telescope. Planck, which carried out an all-sky survey from 2009 to 2013, was primarily designed to observe the Big Bang’s relic light. In the process, the spacecraft compiled measurements of microwave wavelength light from all over the sky. The researchers used a portion of Planck observations that trace emission from dust within the Milky Way relevant to helping map the Local Bubble’s magnetic field.

Specifically, the observations of interest consisted of polarized light, meaning light that vibrates in a preferred direction. This polarization is produced by magnetically aligned dust particles in space. The alignment of the dust in turn speaks to the orientation of the magnetic field acting upon the dust particles. Mapping the magnetic field lines in this way enabled researchers working on the Planck data to compile a 2D map of the magnetic field projected on to the sky as seen from Earth. In order to morph or “de-project” this map into three spatial dimensions, the researchers made two key assumptions: First, that most of the interstellar dust producing the polarization observed lies in the Local Bubble’s surface.

And, second, that theories predicting that the magnetic field would be “swept up” into the bubble’s surface as it expands are correct. O’Neill subsequently carried out the complicated geometrical analysis needed to create the 3D magnetic field map during the summer CfA internship. Goodman likens the research team to pioneering mapmakers who created some of the first maps of Earth. “We’ve 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 technology and our physical understanding improve, we will be able to improve the accuracy of our map and hopefully confirm what we are seeing.” The 3D view of magnetic whorls that emerged represent the magnetic field structure of our neighborhood superbubble, if the field was indeed swept-up into the bubble’s surface, and if most of the polarization is produced there.

The research team further compared the resulting map to features along the Local Bubble’s surface. Examples included the Per-Tau Shell, a giant spherical region of star formation, 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 start to probe the influences of magnetic fields on star formation in superbubbles,” says Goodman. “And for that matter, get a better grasp on how these fields influence numerous other cosmic phenomena.” Because magnetic fields only affect the movement and orientation of charged particles in astrophysical environments, Goodman says there has been a tendency to set aside the fields’ influence when building simulations and theories where 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 magnetic fields’ influence, while understandable, often leaves out a key factor controlling motions of gas 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 disk. Even if the effect of magnetic fields is miniscule from moment-to-moment in the low-density environments where stars form, given the millions-of-year timescales it takes to gather gas and turn it into stars, magnetic effects can plausibly add up to something substantial over time. Goodman, O’Neill, and their colleagues look forward to finding out. “I’ve had a great experience doing this research at CfA and assembling 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 the superbubbles throughout our galaxy.”

“illustration of the Local Bubble with star formation occurring on the bubble’s surface. Scientists have now shown how a chain of events beginning 14 million years ago with a set of powerful supernovae led to the creation of the vast bubble, responsible for the formation of all young stars within 500 light years of the Sun and Earth.”

1,000-light-year wide bubble surrounding Earth is source of all nearby, young stars
by Harvard-Smithsonian Center for Astrophysics  /  January 12, 2022

“The Earth sits in a 1,000-light-year-wide void surrounded by thousands of young stars—but how did those stars form? In a paper appearing Wednesday in Nature, astronomers at the Center for Astrophysics | Harvard & Smithsonian (CfA) and the Space Telescope Science Institute (STScI) reconstruct the evolutionary history of our galactic neighborhood, showing how a chain of events beginning 14 million years ago led to the creation of a vast bubble that’s responsible for the formation of all nearby, young stars.

“This is really an origin story; for the first time we can explain how all nearby star formation began,” says astronomer and data visualization expert Catherine Zucker who completed the work during a fellowship at the CfA. The paper’s central figure, a 3D spacetime animation, reveals that all young stars and star-forming regions—within 500 light years of Earth—sit on the surface of a giant bubble known as the Local Bubble. While astronomers have known of its existence for decades, scientists can now see and understand the Local Bubble’s beginnings and its impact on the gas around it.

Using a trove of new data and data science techniques, the spacetime animation shows how a series of supernovae that first went off 14 million years ago, pushed interstellar gas outwards, creating a bubble-like structure with a surface that’s ripe for star formation. Today, seven well-known star-forming regions or molecular clouds—dense regions in space where stars can form—sit on the surface of the bubble. “We’ve calculated that about 15 supernovae have gone off over millions of years to form the Local Bubble that we see today,” says Zucker who is now a NASA Hubble Fellow at STScI.

The oddly-shaped bubble is not dormant and continues to slowly grow, the astronomers note. “It’s coasting along at about 4 miles per second,” Zucker says. “It has lost most of its oomph though and has pretty much plateaued in terms of speed.” The expansion speed of the bubble, as well as the past and present trajectories of the young stars forming on its surface, were derived using data obtained by Gaia, a space-based observatory launched by the European Space Agency. “This is an incredible detective story, driven by both data and theory,” says Harvard professor and Center for Astrophysics astronomer Alyssa Goodman, a study co-author and founder of glue, data visualization software that enabled the discovery.

“We can piece together the history of star formation around us using a wide variety of independent clues: supernova models, stellar motions and exquisite new 3D maps of the material surrounding the Local Bubble.” “When the first supernovae that created the Local Bubble went off, our Sun was far away from the action” says co-author João Alves, a professor at the University of Vienna. “But about five million years ago, the Sun’s path through the galaxy took it right into the bubble, and now the Sun sits—just by luck—almost right in the bubble’s center.”

Today, as humans peer out into space from near the Sun, they have a front row seat to the process of star formation occurring all around on the bubble’s surface. Astronomers first theorized that superbubbles were pervasive in the Milky Way nearly 50 years ago. “Now, we have proof—and what are the chances that we are right smack in the middle of one of these things?” asks Goodman. Statistically, it is very unlikely that the Sun would be centered in a giant bubble if such bubbles were rare in our Milky Way Galaxy, she explains. Goodman likens the discovery to a Milky Way that resembles very hole-y swiss cheese, where holes in the cheese are blasted out by supernovae, and new stars can form in the cheese around the holes created by dying stars.

Next, the team, including co-author and Harvard doctoral student Michael Foley, plans to map out more interstellar bubbles to get a full 3D view of their locations, shapes and sizes. Charting out bubbles, and their relationship to each other, will ultimately allow astronomers to understand the role played by dying stars in giving birth to new ones, and in the structure and evolution of galaxies like the Milky Way.  Zucker wonders, “Where do these bubbles touch? How do they interact with each other? How do superbubbles drive the birth of stars like our Sun in the Milky Way?”

Additional co-authors on the paper are Douglas Finkbeiner and Diana Khimey of the CfA; Josefa Groβschedland Cameren Swiggum of the University of Vienna; Shmuel Bialy of the University of Maryland; Joshua Speagle of the University of Toronto; and Andreas Burkert of the University Observatory Munich. The articles, analyzed data (on the Harvard Dataverse) and interactive figures and videos are all freely available to everyone through a dedicated website.”

more info: Catherine Zucker, Star formation near the Sun is driven by expansion of the Local Bubble, Nature (2022). DOI: 10.1038/s41586-021-04286-5www.nature.com/articles/s41586-021-04286-5

Nessie, a cloud of cold gas and dust, is a “bone” tracing the Milky Way’s spiral arm structure. Astronomers used SOFIA to measure the magnetic field along the bone G47.06+0.26 via its infrared polarization.”

The magnetic field in the Milky Way filamentary bone G47
by Harvard-Smithsonian Center for Astrophysics  /  February 7, 2022

“Star formation in the Milky Way primarily occurs in long, dense filaments of gas and dust that stretch along the spiral arms. Dubbed “bones” because they delineate the galaxy’s densest skeletal spiral structures, these filaments are characterized by being at least fifty times longer than they are wide and having coherent internal motions along their lengths. While most of the key physical properties of these bones are known, what we know of their magnetic field properties is generally unconstrained.

These fields can play a critical role either in supporting the gas and dust against gravitational collapse into new stars, or alternatively, in assisting the flow of mass along the bone into cores making new stars. Magnetic fields are notoriously difficult to measure in space. The most common method relies on the emission from non-spherical dust grains that align their short axes with the direction of the field, resulting in infrared radiation that is preferentially polarized perpendicular to the field. Measuring this faint polarization signal, and inferring the field strength and direction, has only recently become easier to do with the HAWC+ instrument on SOFIA, NASA’s Stratospheric Observatory for Infrared Astronomy, and its 2.5-m telescope.

SOFIA flies as high as 45,000 feet, above most of the atmospheric water vapor that absorbs far infrared infrared signals from space. CfA astronomers Ian Stephens, Phil Myers, Catherine Zucker, and Howard Smith led a team that used HAWC+ polarization to map the detailed magnetic field along the bone G47.06+0.26. This filament is about 190 light-years long, five light-years across, and has a mass of 28,000 solar-masses with a typical dust temperature of 18 kelvin. The IRAC camera on Spitzer had previously mapped the bone to identify the regions of young star formation along its length.

The astronomers determined where along the bone the magnetic field is capable of supporting the gas against collapse into stars, and those regions where it is too weak. They also mapped low density regions where the field is more complex in shape. G47.06+0.26 is just the first object studied in a larger program to map the magnetic fields in ten of the eighteen known Milky Way bones. Once an analysis of this larger statistical sample has been completed, the scientists expect to be able to quantify more precisely how the strength and orientation of fields influence the evolution of the bones and their pockets of star formation.”

more info: Ian W. Stephens et al, The Magnetic Field in the Milky Way Filamentary Bone G47. arXiv:2201.11933v1 [astro-ph.GA], arxiv.org/abs/2201.11933

“Astronomers have discovered a giant, spherical cavity within the Milky Way galaxy; its location is depicted on the right. A zoomed in view of the cavity (left) shows the Perseus and Taurus molecular clouds in blue and red, respectively. Though they appear to sit within the cavity and touch, new 3D images of the clouds show they border the cavity and are quite a distance apart. This image was produced in glue using the WorldWide Telescope.”

Gigantic cavity in space sheds new light on how stars form
by Harvard-Smithsonian Center for Astrophysics  /  September 22, 2021

“Astronomers analyzing 3D maps of the shapes and sizes of nearby molecular clouds have discovered a gigantic cavity in space. The sphere-shaped void, described today in the Astrophysical Journal Letters, spans about 150 parsecs—nearly 500 light years—and is located on the sky among the constellations Perseus and Taurus. The research team, which is based at the Center for Astrophysics | Harvard & Smithsonian, believes the cavity was formed by ancient supernovae that went off some 10 million years ago. The mysterious cavity is surrounded by the Perseus and Taurus molecular clouds—regions in space where stars form. “Hundreds of stars are forming or exist already at the surface of this giant bubble,” says Shmuel Bialy, a postdoctoral researcher at the Institute for Theory and Computation (ITC) at the Center for Astrophysics (CfA) who led the study. “We have two theories—either one supernova went off at the core of this bubble and pushed gas outward forming what we now call the ‘Perseus-Taurus Supershell,’ or a series of supernovae occurring over millions of years created it over time.”

The finding suggests that the Perseus and Taurus molecular clouds are not independent structures in space. But rather, they formed together from the very same supernova shockwave. “This demonstrates that when a star dies, its supernova generates a chain of events that may ultimately lead to the birth of new stars,” Bialy explains. The 3D map of the bubble and surrounding clouds were created using new data from Gaia, a space-based observatory launched by the European Space Agency (ESA). Descriptions of exactly how 3D maps of the Perseus and Taurus molecular clouds and other nearby clouds were analyzed appear in a separate study published today in the Astrophysical Journal (ApJ). Both studies make use of a dust reconstruction created by researchers at the Max Planck Institute for Astronomy in Germany.  The maps represent the first-time molecular clouds have been charted in 3D. Previous images of the clouds were constrained to two dimensions.

“We’ve been able to see these clouds for decades, but we never knew their true shape, depth or thickness. We also were unsure how far away the clouds were,” says Catherine Zucker, a postdoctoral researcher at the CfA who led the ApJ study. “Now we know where they lie with only 1 percent uncertainty, allowing us to discern this void between them.” But why map clouds in the first place? “There are many different theories for how gas rearranges itself to form stars,” Zucker explains. “Astronomers have tested these theoretical ideas using simulations in the past, but this is the first time we can use real—not simulated—3D views to compare theory to observation, and evaluate which theories work best.” The new research marks the first time journals of the American Astronomical Society (AAS) publish astronomy visualizations in augmented reality. Scientists and the public may interact with the visualization of the cavity and its surrounding molecular clouds by simply scanning a QR code in the paper with their smartphone.

“You can literally make the universe float over your kitchen table,” says Harvard professor and CfA astronomer Alyssa Goodman, a co-author on both studies and founder of glue, the data visualization software that was used to create the maps of molecular clouds. Goodman calls the new publications examples of the “paper of the future” and considers them important steps toward the interactivity and reproducibility of science, which AAS committed to in 2015 as part of their effort to modernize publications. “We need richer records of scientific discovery,” Goodman says. “And current scholarly papers could be doing much better. All of the data in these papers are available online—on Harvard’s Dataverse—so that anyone can build on our results.” Goodman envisions future scientific articles where audio, video and enhanced visuals are regularly included, allowing all readers to more easily understand the research presented. She says, “It’s 3D visualizations like these that can help both scientists and the public understand what’s happening in space and the powerful effects of supernovae.”

more info: Astrophysical Journal Letters (2021). iopscience.iop.org/article/10. … 847/2041-8213/ac1f95 Astrophysical Journal (2021). iopscience.iop.org/article/10.3847/1538-435

“An image of the magnetized, star-forming core BHR 71 IRS1. The outermost low- density gas is shown by the blue and white background colors; the centrally concentrated core gas is shown by the black contour lines and green color. The central protostar and planet-forming disk are shown by the orange circle. The associated magnetic field lines are shown by the curved white lines, whose shape indicates that the field has been pulled inward by the contracting dense gas . Astronomers have completed the first analysis of magnetic field influences in star-forming cores using a combination of techniques. Credit: Myers et al. 2020”

The magnetic properties of star-forming dense cores
by Harvard-Smithsonian Center for Astrophysics  /  August 31, 2021

“Magnetic fields in space are sometimes called the last piece in the puzzle of star formation. They are much harder to measure than the masses or motions of star-forming clouds, and their strength is still uncertain. If they are strong, they can deflect or even oppose gas flowing into a young stellar core as it collapses under the influence of gravity. If they are moderate in strength, however, they act more flexibly and guide the flow, but don’t prevent it. Early measurements of field strengths in molecular clouds were based on radiation from molecules whose energy levels are sensitive to magnetic field strengths. Those data suggested the fields were of moderate strength, but those conclusions were tentative. More recent observations with stronger signals measured the polarized radiation from dust grains aligned with the magnetic field. These observations obtain the field strength from the changes in field direction across the cloud map.

CfA astronomer Phil Myers and his collaborator undertook to clarify the role of magnetic fields in star-forming cloud cores. They compared field strengths using the dust technique in 17 cores forming low mass stars and using the molecular technique in 36 cores forming more massive stars. The two techniques find nearly the same properties for the fields, despite each measuring a different magnetic effect. The astronomers analyzed whether the fields are strong enough to prevent gravitational collapse, and how their strengths scale with density. They find that, despite the diverse range of core properties, none of the fields is strong enough (by a factor of two or three) to prevent collapse. They also find correlations between field strength, density, and other core properties which are consistent with theoretical expectations. This study is the first analysis of magnetic field influences in star-forming cores using both molecular and dust measurement techniques, and it corroborates and extends the earlier findings based on the molecular technique alone.”

more info: Philip C. Myers et al, Magnetic Properties of Star-forming Dense Cores, The Astrophysical Journal (2021). DOI: 10.3847/1538-4357/abf4c8

“Fig. 1 Core-scale magnetic fields (red segments) inferred using high-resolution and sensitive dust emission polarization observations using JCMT. The Solar-type star forming cores fragmented out of B213 filament are shown”

Study reveals diverse magnetic fields in solar-type star forming cores
by Li Yuan, Chinese Academy of Sciences  /  June 1, 2021

“Magnetic fields are ubiquitous throughout the Milky Way galaxy and play a crucial role in all dynamics of interstellar medium. However, questions like how solar-type stars form out of magnetized molecular clouds, whether the role of magnetic fields changes at various scales and densities of molecular clouds, and what factors can change the morphology of magnetic fields in low-mass dense cores still remain unclear. A new study led by Dr. Eswaraiah Chakali from Prof. Li Di‘s research group at the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) has partially answered these questions.

The study reveals the diverse magnetic field morphologies in solar-type star forming cores in the Taurus B213 region. This study was published in The Astrophysical Journal Letters on May 10. The researchers used high-resolution and sensitive 850-micron dust emission polarization data acquired by the James Clerk Maxwell Telescope (JCMT) using the SCUBA-2 camera along with the POL-2 polarimeter. The observations were conducted as a part of a large international program called B-fields In STar-forming Region Observations (BISTRO). “Although formed out of the same filamentary cloud, Taurus/B213, among the three dense cores having more polarization measurements, only one remembers the relatively uniform large-scale magnetic field threading the parental cloud,” said Dr. Eswaraiah Chakali, lead author of the study.

“Fig. 2 Large-scale, uniform magnetic field morphology of Taurus/B213 region, inferred based on multi-wavelength polarization data. The extent of Fig. 1 is marked with a white box. Credit: Eswaraiah Chakali, et al. 2021”

This is in contrast to expectations based on the theory that magnetic fields regulate star formation. If a large-scale magnetic field dominates throughout cloud accumulation, core collapse and star formation, the mean position angle of the magnetic field should be similar across various spatial scales. Further analysis of the gas velocity gradient revealed that the kinematics due to gas accretion flows onto the parental filament could have altered the magnetic field configuration. “Even in the presence of substantial magnetic flux, local physical conditions can significantly affect magnetic field morphology and their role in star formation,” said Prof. Li Di, co-corresponding author of the study. “Our current observations represent one of the deepest sub-millimeter polarimetry images ever taken using a single dish telescope toward a Galactic region,” said Prof. Qiu Keping of Nanjing University, co-PI of the BISTRO project and a coauthor of the study. Prof. Li Di also highlighted “more comprehensive analyses, in combination with Planck data and stellar polarimetry, may give more insights into the evolution of magnetic fields in this stereotypical low-mass star-forming region.”

more info: Eswaraiah Chakali et al, The JCMT BISTRO Survey: Revealing the Diverse Magnetic Field Morphologies in Taurus Dense Cores with Sensitive Submillimeter Polarimetry, The Astrophysical Journal Letters (2021). DOI: 10.3847/2041-8213/abeb1c

“Rho Ophiuchi cloud complex viewed by Herschel and Planck”

Herschel and Planck views of star formation
by European Space Agency / July 6, 2020

“A collection of intriguing images based on data from ESA’s Herschel and Planck space telescopes show the influence of magnetic fields on the clouds of gas and dust where stars are forming. The images are part of a study by astronomer Juan D. Soler of the Max Planck Institute for Astronomy in Heidelberg, Germany, who used data gathered during Planck’s all-sky observations and Herschel’s ‘Gould Belt Survey’.

“Chamaeleon I molecular cloud viewed by Herschel and Planck”

Both Herschel and Planck were instrumental in exploring the cool Universe, and shed light on the many complexities of the interstellar medium – the mix of gas and dust that fills the space between the stars in a galaxy. Both telescopes ended their operational lifetime in 2013, but new discoveries continue to be made from their treasure trove of data. Herschel revealed in unprecedented detail the filaments of dense material in molecular clouds across our Milky Way galaxy, and their key role in the process of star formation. Filaments can fragment into clumps which eventually collapse into stars.

“Lupus cloud complex viewed by Herschel and Planck”

The results from Herschel show a close link between filament structure and the presence of dense clumps. Herschel observed the sky in far-infrared and sub-millimetre wavelengths, and the data is seen in these images as a mixture of different colours, with light emitted by interstellar dust grains mixed within the gas. The texture of faint grey bands stretching across the images like a drapery pattern, is based on Planck’s measurements of the direction of the polarised light emitted by the dust and show the orientation of the magnetic field.

“Corona Australis molecular cloud viewed by Herschel and Planck”

The study explored several nearby molecular clouds all within 1500 light years from the Sun including Taurus, Ophiuchus, Lupus, Corona Australis, Chamaeleon-Musca, Aquila Rift, Perseus, and Orion.”



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