Astronomers have mapped a vast “magnetic superhighway” powering intense star formation and violent 1.1 million miles per hour (500 kilometers per second) galactic winds inside the merging galaxy system Arp 220. Using the Atacama Large Millimeter/submillimeter Array (ALMA), the international research team has produced the most detailed magnetic map ever made of this cosmic collision.
Arp 220, located about 250 million light-years from Earth, is an ultraluminous infrared galaxy (meaning it shines as bright as one hundred or more Milky Way galaxies) formed by the ongoing merger of two spiral galaxies. Shrouded in thick dust, it shines intensely in infrared light and serves as a nearby stand-in for the extreme, star-forming galaxies that dominated the early universe. By studying Arp 220, astronomers gain a rare window into processes that shaped massive galaxies more than 10 billion years ago.
The team’s results have uncovered that its fast-moving molecular outflows are threaded by strong, organized magnetic structures.
“This revealed previously unseen details about Arp 220’s dust-enshrouded cores and molecular outflows,” said Josep Miquel Girart, the study’s lead in the observational work, and a researcher at the Institut de Ciències de l’Espai.
Magnetic fields launch powerful cosmic winds
The new observations show that magnetic fields play a central role in launching and shaping the powerful winds streaming from Arp 220’s twin cores. These winds, traveling at speeds 1,500 times the speed of sound here on Earth, carry gas, dust, metals, and cosmic rays far beyond the galaxy itself. Until now, the forces behind such outflows were thought to be driven mainly by intense star formation and possible black hole activity.
However, using ALMA’s high-resolution polarization capabilities, the researchers traced how microscopic dust grains and carbon monoxide molecules align with magnetic fields. This allowed them to reconstruct the three-dimensional geometry of the fields within the galaxy and along its outflows.
The result is a striking image of what the scientists describe as a nearly vertical channel of magnetized gas streaming outward from one of the galaxy’s nuclei, which they dubbed a “magnetic superhighway.”
In the western core of Arp 220, the team observed a well-ordered magnetic structure closely aligned with the bipolar outflow. This indicates that the magnetic field is not merely going along for the ride but is actively guiding and accelerating the escaping material. Meanwhile, the eastern core revealed a spiral-shaped magnetic pattern embedded within a dense, rotating disk, suggesting that large-scale magnetic order can survive even in the turbulent environment of a galaxy merger.
Perhaps the most intriguing aspect of this investigation was the discovery of a highly polarized bridge of dust connecting the two galactic centers. This magnetized ridge appears to funnel material and magnetic flux between the merging nuclei, further emphasizing the role of magnetic fields in governing the flow of matter during galactic collisions.
“When Arp 220 is observed as a whole, it’s one of the best places in the universe for astronomers to study how gravity, star formation, and powerful winds work together with strong magnetic fields to reshape a galaxy and seed its surroundings with magnetized gas and dust,” said Lopez-Rodriguez.
Measurements indicate that the magnetic fields in these outflows are extraordinarily strong, reaching intensities hundreds to thousands of times greater than those typically found in the Milky Way. Such powerful fields can significantly influence how gas moves, cools, and eventually forms new stars, while also regulating how galaxies lose material to their surroundings.
These findings suggest that strong, organized magnetic fields may have been common in the early universe, especially in dusty starburst galaxies like Arp 220’s ancient counterparts. By shaping galactic winds, magnetism could have played a major role in determining when galaxies stop forming stars and how they enrich the vast spaces between galaxies.
As astronomers extend these techniques to more distant systems, they expect to find similar magnetic highways throughout the cosmos. For now, Arp 220 stands as a vivid reminder that invisible forces can leave an enduring mark on the visible universe.
The team’s research was published on Jan. 2 in The Astrophysical Journal Letters.
