SPACE/COSMOS
Galactic Rosetta Stone: Study measuring magnetic field near the center of the Milky Way helps to decode the precise astrophysical dynamics at the heart of our galaxy
University of Chicago
image:
A view of the center of our galaxy shows the Sagittarius C (Sgr C) region, where cold dust (magenta) and warmer gas and dust (cyan) surround a cluster of massive stars. The stars generate high-speed electrons (yellow) and shape the region’s magnetic fields (striped lines), producing a bright yellow filament—a stream of fast-moving electrons. Image by David Chuss, Kaitlyn Karpovich, and Roy Zhao using data from the Spitzer Space Telescope, ESA’s Herschel Space Telescope, and MeerKAT.
view moreCredit: Image by David Chuss, Kaitlyn Karpovich, and Roy Zhao using data from the Spitzer Space Telescope, ESA’s Herschel Space Telescope, and MeerKAT.
The underlying physics governing the center of our galaxy (the Galactic Center), due to its chaotic and complex nature, has been difficult to observe, model, and predict. Studying the region’s interactions and the environment where they occur helps to unravel the mystery and lead to a better understanding of the center of our, and even other, galaxies.
The central region of the Milky Way, known as the Central Molecular Zone (CMZ), is a vast reservoir of interstellar gas and dust orbiting the center of the galaxy and an ideal place to study astrophysics in extreme environments. One particular site within the CMZ named Sagittarius C (Sgr C) is known for intriguing cloud and filamentary features, complex dynamical structure, and massive star formation.
To better understand this region of space, a team including Roy Zhao, a second-year PhD student in the Department of Physics and the Kavli Institute for Cosmological Physics, measured the magnetic field of Sgr C, publishing the results in the Astrophysical Journal.
Zhao, the first author on the study, currently works with Professor Emeritus Josh Frieman and Associate Professor Chihway Chang in the Astronomy and Astrophysics Department. He investigates the astrophysics of galaxies across the history of the universe, recently shifted to applying novel data-driven techniques to the study of cosmology.
This study originated when Zhao was a researcher at UCLA, in collaboration with Distinguished Professor Emeritus Mark Morris, PhD’75. Zhao presented his research at the American Astronomical Society’s 244th meeting and describes its goals, major findings, and next steps in the Q&A below.
How was the study conducted?
Sagittarius C is known to be a bright radio and infrared source. To better understand the status of this region, we studied the magnetic field there by observing the infrared light emitted by the interstellar dust grains peppered through the clouds. The dust grains are aligned by the magnetic field like compasses, so the infrared light they emit is polarized and can therefore be used to infer the orientation of the magnetic field. The observation was done by NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA), a Boeing 737 modified into a flying telescope, which was retired in 2022.
In our galaxy, this region constitutes the astrophysical “Rosetta Stone,” allowing us to piece together the interaction between three key components—dense clouds, star formation, and the relatively strong magnetic field—and what such interaction may cause (e.g. excessive star formation, strong stream of free electrons, etc.). Direct observation of the magnetic field plays an important role in deciphering this myth.
What are your key findings and their implications?
We found that the magnetic field is an excellent probe of the local environment. The magnetic field appears to wrap around an expanding central bubble of hot, ionized gas. This bubble has apparently been created by the powerful winds of a group of massive young stars, and those winds have compressed and accelerated the dense gas and its magnetic field into the observed expanding bubble.
Back in the 1980s, my advisor and second author of this work, Prof. Mark Morris, co-discovered the existence of radio-emitting filaments (the thin streams of high-speed electrons) in the dynamical center of the Milky Way called the Galactic Center. Since then, many hypotheses have been proposed regarding their formation. Our study found that the magnetic field geometry near the origin of the filament supports one of the leading hypotheses, known as magnetic field line reconnection, where two merging fields accelerate the nearby electrons to close to the speed of light and form these filaments. This theory can now be applied to many other radio filaments that span the Galactic Center region.
Meanwhile, we have also learned how star-formation regions, cold clouds, and hot, ionized regions interact with each other and how the shape of the magnetic field may have a profound impact in determining the outcome of the interaction. These lessons learned from this “Rosetta Stone” can be applied to other parts of our galaxy, so scientists can reconstruct the events taking place in such regions.
What are the next steps?
Our study was done with one wavelength of light (214 microns), which probes only colder clouds. As such, our results cannot speak fully to the magnetic field of hotter regions that are heated by sources such as stars. To have a complete picture of what’s happening in the region, we also require an understanding of the dynamics inside these warm regions. Therefore, a natural next step would be to carry out a similar survey at a different wavelength.
What led you to investigate this question?
While the Sgr C region is one of the most active star-forming sites in the Galactic Center, it has historically received far less attention, especially compared to Sgr A*, a nearby supermassive blackhole. However, Sgr C is of particular interest since it provides us with direct access to an ongoing interaction with three components: a bubble of ionized gas, cold clouds with active star-formation, and the radio filaments. The astrophysics waiting to be uncovered in this region is rich and will lead to a better understanding of the dynamics of our own galaxy.
Did anything about this work surprise you?
The most surprising part of this work was observing the amazing correspondence between our magnetic field measurement and other surveys conducted in the same region. For example, our results showed that the central HII region (the hot, ionized region) forms a blown-up bubble, where the magnetic field overlaps perfectly with a shell indicated by the [CII] emission line—a bright spectral line produced by singly ionized carbon atoms in clouds excited by the UV radiation from stars—measured by another SOFIA survey. Through some further investigation, we found a powerful star (called a Wolf-Rayet star) at the center of the bubble that may have created it. It was a very satisfying moment to see different pieces of the puzzle fit together seamlessly!
Citation: "SOFIA/HAWC+ Far-infrared Polarimetric Large Area CMZ Exploration Survey. V. The Magnetic Field Strength and Morphology in the Sagittarius C Complex." Roy J. Zhao et al 2025 ApJ 988 252.
Journal
The Astrophysical Journal
Article Title
SOFIA/HAWC+ Far-infrared Polarimetric Large Area CMZ Exploration Survey. V. The Magnetic Field Strength and Morphology in the Sagittarius C Complex
Breakthrough model explains origins of black holes and early cosmic ionization
A new theoretical study by University of Virginia astrophysicist Jonathan Tan, a research professor with the College and Graduate School of Arts & Sciences’ Department of Astronomy, proposes a comprehensive framework for the birth of supermassive black holes. These mysterious behemoths lurk in the centers of most large galaxies, including our own Milky Way and are typically millions or even billions of times more massive than the Sun. Their formation has been much debated, especially as the James Webb Space Telescope (JWST) has been finding many such black holes that exist far away and that have existed as far back in time as the dawn of the universe. Tan’s theory, known as “Pop III.1” proposes that all supermassive black holes form as the remnants of the very first, so-called “Population III.1” stars, the very first stars in the universe which grew to enormous sizes under the influence of energy from a process known as dark matter annihilation, and the theory has predicted many of the JWST’s recent findings.
In his paper, "Flash Ionization of the Early Universe by Pop III.1 Supermassive Stars," published in Astrophysical Journal Letters, Tan, who is also a professor in the Department of Space, Earth and Environment at Chalmers University of Technology, Gothenburg, Sweden, outlines another prediction of the theory that could shed new light on the origins of the universe.
“Our model requires that the supermassive star progenitors of the black holes rapidly ionized the hydrogen gas in the universe, announcing their birth with bright flashes that filled all of space,” Tan said. Intriguingly this extra phase of ionization, occurring much earlier than that powered by normal galaxies, may help resolve some recent conundrums and tensions that have arisen in cosmology, including the “Hubble Tension”, “Dynamic Dark Energy” and preference for “Negative Neutrino Masses,” all of which challenge the standard model of the universe,” Tan said. “It’s a connection we didn’t anticipate when developing the Pop III.1 model, but it may prove profoundly important.”
The study has been praised by Richard Ellis, one of the world’s leading observational cosmologists and a professor of astrophysics at University College London who has spent decades studying the formation of the earliest galaxies and the first light in the universe. “Professor Tan has developed an elegant model that could explain a two-stage process of stellar birth and ionization in the early universe,” said Ellis. “It’s possible the very first stars formed in a brief, brilliant flash, then vanished — meaning what we now see with the James Webb Telescope may be just the second wave. The universe, it seems, still holds surprises.”
Article Title
Astrophysical Journal Letters
Article Publication Date
12-Aug-2025
Studying terrestrial rocks to prepare techniques for Mars
Learning how to study the leopardlike spots found on both terrestrial and Martian rocks can prepare scientists for when the real samples arrive from space
American Institute of Physics
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The original, untreated sample Heinz picked up on his Sedona hike, with spots similar to spots on the Mars Sapphire Canyon rock.
view moreCredit: Nicholas Heinz
WASHINGTON, August 12, 2025 – In 2024, NASA’s Mars rover Perseverance collected an unusual rock sample. The rock, named Sapphire Canyon, features white, leopardlike spots with black borders within a red mudstone and might hold clues about sources of organic molecules within Mars.
Here on Earth, in Review of Scientific Instruments, by AIP Publishing, researchers from Jet Propulsion Laboratory and the California Institute of Technology used a technique called optical photothermal infrared spectroscopy (O-PTIR) to study a visually similar rock. They wanted to determine if O-PTIR can be applied to the Sapphire Canyon sample when it is eventually brought here for study.
O-PTIR uses two lasers to study a material: The first heats up the material and causes small thermal vibrations on its surface proportional to the laser’s wavelength, and the second measures the extent of these changes. Together, this creates the material’s unique chemical fingerprint.
The researchers tested O-PTIR on a basalt rock with dark inclusions of similar size to the Sapphire Canyon sample’s — which, in contrast to Perseverance’s sophisticated sample selection process, author Nicholas Heinz found purely by coincidence.
“I was hiking in Arizona, in Sedona, when I saw this rock that just didn’t look like it belonged,” he said. “I put it in my backpack and brought it back to look at.”
They aimed to see if O-PTIR could differentiate between the rock’s primary material and its dark inclusions and found it was extremely effective because of the enhanced spatial resolution of O-PTIR. Moreover, O-PTIR is a rapid technique. Each spectrum can be collected in minutes, allowing scientists to go in with a more sensitive technique to study potential areas of interest identified in more detail, such as regions containing organics.
“I hope this capability will be considered for any future material returned from Mars, an asteroid, or any other planetary surface,” said Heinz.
The team’s O-PTIR capabilities are the only of their kind available at NASA’s Jet Propulsion Laboratory and have already been used by other NASA missions — in 2024, they helped confirm the cleanliness of Europa Clipper, a mission to study one of Jupiter’s moons, prior to its launch. Heinz said that now that they’ve shown its additional benefits in applications related to Mars samples, and geology more widely, they are working with NASA’s Mars science team to test the algal microfossils typically used as Mars analogs for the rovers.
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The article “Application of optical photothermal infrared spectroscopy (O-PTIR) for future returned Mars samples” is authored by Nicholas Heinz, Mark S. Anderson, Jerami Mennella, and George R. Rossman. It will appear in Review of Scientific Instruments on August 12, 2025 (DOI: 10.1063/5.0266350). After that date, it can be accessed at https://doi.org/10.1063/5.0266350.
ABOUT THE JOURNAL
Review of Scientific Instruments publishes novel advancements in scientific instrumentation, apparatuses, techniques of experimental measurement, and related mathematical analysis. Its content includes publication on instruments covering all areas of science including physics, chemistry, materials science, and biology. See https://pubs.aip.org/aip/rsi.
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Journal
Review of Scientific Instruments
Article Title
Application of optical photothermal infrared spectroscopy (O-PTIR) for future returned Mars samples
Article Publication Date
12-Aug-2025
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