Can We Unlock the Mysteries of Starburst Galaxies with Magnetic Fields?
Galactic Mergers: Chaotic Events with Surprising Outcomes
A galactic merger is a chaotic and dynamic process. When two massive structures like galaxies collide, their immense gravitational forces disrupt the stable orbits of stars in a phenomenon known as violent relaxation. This results in rapid and unpredictable changes as the galaxies move toward a new state of equilibrium.
Conventional wisdom suggests that such turbulence should hinder star formation. However, recent observations of the Arp 220 galaxy merger reveal a different story. Rather than suppressing star formation, the merger generates a colossal magnetic field that traps gas, fostering the creation of new stars.
Arp 220: A Prototypical Ultraluminous Infrared Galaxy (ULIRG)
Arp 220 stands out as one of the nearest galaxy mergers to Earth. Its intense infrared brightness has earned it the title of a prototypical ULIRG—an Ultraluminous Infrared Galaxy. This extraordinary galaxy formed from the merger of two gas-rich spiral galaxies, triggering intense starburst activity in its core regions.
Researchers from the Harvard and Smithsonian Center for Astrophysics, alongside other institutions, recently studied Arp 220’s central regions using the Submillimeter Array (SMA) on Maunakea in Hawaii. Their goal was to better understand the role of magnetic fields in star formation during galactic mergers.
Groundbreaking Research with the Submillimeter Array
The study, titled “Polarized Dust Emission in Arp220: Magnetic Fields in the Core of an Ultraluminous Infrared Galaxy,” will be published in the Monthly Notices of the Royal Astronomical Society. Led by David Clements from the Department of Physics at Imperial College London, the research team made significant discoveries about magnetic fields in Arp 220.
Detecting Magnetic Fields through Polarized Dust
ULIRGs like Arp 220 exhibit intense star formation and extraordinary infrared luminosity. “Arp 220 is the merger of two gas-rich spiral galaxies and hosts a massive starburst forming stars at a rate of about 100 solar masses per year,” the authors explain. This star formation is concentrated in two distinct nuclei at the galaxy’s center.
The researchers utilized the SMA to detect polarized light emitted by dust grains. These grains align with magnetic fields, allowing scientists to infer the properties of the fields by measuring light polarity.
“Despite the potential impact of magnetic fields on galaxy structure, sub-mm observations of polarization in extragalactic sources remain sparse,” the authors note. Previous attempts, including observations from SOFIA (Stratospheric Observatory for Infrared Astronomy), lacked the resolution to distinguish between the two nuclei in Arp 220.
The team overcame this limitation by achieving subarcsecond resolution, enabling them to resolve the separate nuclei and avoid polarization dilution.
Strong Evidence of Magnetic Fields
The researchers detected polarized dust emission with a 6-sigma significance—a highly robust detection level—associated with the brighter, western nucleus of Arp 220. This strong detection suggests the presence of powerful magnetic fields.
Magnetic Fields: The Key to Sustaining Starburst Activity
Unexpected Magnetic Field Orientations
Interestingly, the magnetic fields in Arp 220 do not align with galactic outflow directions, unlike what has been observed in other nearby galaxies.
The researchers noted that the dust emission polarization is oriented roughly perpendicular to the molecular disk in the western nucleus. This perpendicular alignment suggests that the magnetic field lies in the plane of the galactic disk. However, ongoing interactions between the nuclei may be reordering the magnetic field, underscoring the complexity of the merger environment.
A New Frontier for Understanding Starburst Galaxies
Finding magnetic fields in Arp 220 strongly suggests that they play a crucial role in driving unexpected starburst activity. However, this discovery represents only one data point. A larger sample of observations is necessary to confirm these findings.
The research team plans to use the Atacama Large Millimeter/submillimeter Array (ALMA), the SMA’s more advanced counterpart, to study other galaxies similar to Arp 220.
“While the observations described here deal with just a single target, the nearest and brightest ULIRG, Arp 220, they suggest that magnetic fields may play a significant role in the processes underway in the innermost regions of major mergers,” the authors conclude. “Observations in search of dust polarization in the inner regions of other local ULIRGs and DSFGs (Dusty Star-Forming Galaxies) are likely to bring new insights into these objects and how they evolve.”
Conclusion: Unlocking the Secrets of Star Formation
The discovery of magnetic fields in Arp 220’s core sheds new light on the mechanisms behind star formation during galactic mergers. By holding gas together and slowing its rotation, these magnetic fields enable the formation of new stars despite the chaotic environment.
Future research with ALMA and other advanced instruments promises to deepen our understanding of these enigmatic processes, helping astronomers piece together the complex puzzle of galaxy evolution.
Source: Can We Unlock the Mysteries of Starburst Galaxies with Magnetic Fields?
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Can We Unlock the Mysteries of Starburst Galaxies with Magnetic Fields?