Magnetic “superhighways” mapped in the winds of a galaxy with bursts of star formation

Arp 220 is an ultraluminous infrared galaxy made up of two spiral galaxies in the final stages of merging. Because Arp 220 is the nearest galaxy of its kind, it serves as a powerful time machine: what happens here today likely mirrors what happened in the first generations of massive, dusty galaxies more than 10 billion years ago.

An international team led by the University of South Carolina (USC), with the participation of researchers from the Institute of Space Studies of Catalonia (IEEC) at the Institute of Space Sciences (ICE-CSIC) and at the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) has used the Atacama Large Millimeter/submillimeter Array (ALMA) to map a magnetic “highway” driving a powerful galactic wind into the nearby galaxy merger of Arp 220. The study, which also has the collaboration of the Instituto de Astrofísica de Andalucía (IAA-CSIC), reveals for the first time that Arp 220’s rapid molecular flows are strongly magnetized and they probably contribute to transporting metals, dust and cosmic rays into the space surrounding the galaxy.

By watching how tiny dust grains and gas molecules line up with these fields, the team has drawn the most detailed magnetic map yet of Arp 220’s buried, star‑forming cores and their outflows. The result is a new way to see how gravity, starbirth, black holes, and magnetic forces all work together in a chaotic cosmic environment.

“We used ALMA to map the orientation and strength of magnetic fields in the twin galaxies,” shared Enrique Lopez-Rodriguez, the lead author of this research, and an Associate Professor with the USC. “This revealed previously unseen details about Arp 220’s dust-enshrouded cores and molecular outflows, including the first detection of a polarized CO(3–2) molecular line emission,” adds Josep Miquel Girart, the lead in the observational work, and an IEEC researcher at the ICE-CSIC. This emission traced the galactic outflow in the external galaxy, showing that the outflowing gas itself carries a well-ordered magnetic field.

Observations of the west nucleus of Arp 220 revealed a nearly vertical magnetic field that runs alongside a bipolar molecular outflow moving at up to roughly 500 kilometers per second, driving a powerful, magnetic superhighway out of the galaxy. Galaxy mergers and starbursts are known to launch powerful winds that can shut down, or regulate, star formation by removing gas. However, these new results show that magnetic fields are a crucial, previously unknown driver in the force of these winds.

The team used ALMA to observe the polarized light emitted by the dust and gas of Arp 220, allowing them to trace the magnetic fields in its densest regions and in the powerful winds emanating from the galaxy. These observations provided a detailed view of how magnetic fields are organized around star-forming nuclei and along the flows of material ejected into space.

By combining this information with data on the movement and amount of gas, the experts were able to estimate the intensity of the magnetic fields and analyze their role in the dynamics of galactic winds. In the eastern nucleus, ALMA revealed a spiral-like magnetic pattern threading a compact, dust-enshrouded disk and arm, suggesting that ordered spiral fields can survive deep into the merger stage.

Because Arp 220 is the closest analog to the extreme, dusty star-forming galaxies in the early Universe, these results suggest that strong, organized magnetic fields may be common in high-redshift starbursts and could play a key role in regulating star formation and feedback across cosmic time.

These ALMA observations show that magnetic fields are a major engine in driving material out of galaxies like Arp 220. The strong, ordered fields in its galactic winds act like invisible guardrails, guiding metals, dust, and cosmic rays into the vast cocoon of gas surrounding the system.

That material will eventually help build and enrich future generations of stars and galaxies. As astronomers turn ALMA and future telescopes toward ever more distant galaxies, they expect to find similar magnetic “superhighways” at work across the cosmos. Arp 220 reveals itself as a fundamental piece to understand how galaxies transform over time and how those processes have shaped the Universe we observe today.