The universe isn’t just expanding—it’s colliding. When galaxies meet, they don’t simply crash and burn. They perform an elaborate dance, stretching and pulling at each other across hundreds of millions of years, creating cosmic art that tells the story of stellar birth and death.
The James Webb Space Telescope has captured one such performance in stunning detail: Arp 107, a pair of galaxies caught mid-merger some 465 million light-years away in the constellation Leo Minor.
What makes this image particularly remarkable isn’t just its beauty—it’s what it reveals about the process of galactic evolution.
The larger spiral galaxy appears to be smiling back at us, with two bright “eyes” and a wide semicircular “smile,” a cosmic emoji created by the gravitational forces of its smaller elliptical companion.
But there’s more here than meets the human eye. The bright diffraction spikes emanating from the center of the larger galaxy aren’t just an artifact of the telescope’s optics—they’re evidence of an actively feeding supermassive black hole.
When Galaxies Collide: Creative Destruction
Galactic collisions might sound catastrophic, but they’re actually engines of creation. The compression of gas clouds during these encounters triggers intense bursts of star formation, breathing new life into otherwise aging stellar populations.
This isn’t the first time astronomers have observed Arp 107. NASA’s Spitzer Space Telescope captured it in infrared back in 2005. But Webb’s advanced instruments provide unprecedented clarity, revealing details previously hidden from view.
The new image combines data from Webb’s NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument). NIRCam highlights the stars within both galaxies and reveals the connection between them—a transparent, white bridge of stars and gas pulled from both galaxies during their cosmic encounter.
MIRI data, shown in orange-red, reveals star-forming regions and dust composed of organic molecules known as polycyclic aromatic hydrocarbons. These compounds are the cosmic equivalent of soot, yet they’re fundamental building blocks for more complex chemistry.
Not All Collisions Are Created Equal
Here’s where conventional wisdom about galactic mergers gets interesting: the outcome of these cosmic collisions depends heavily on the angle and speed of approach.
Unlike the Cartwheel Galaxy—another interacting system Webb observed early in its mission—Arp 107 experienced an off-center collision rather than a direct hit. This glancing blow allowed the spiral galaxy to maintain much of its structure, with only its spiral arms being significantly disturbed.
Had the smaller elliptical galaxy plunged directly through the center of its spiral partner, we might be looking at something much more resembling the Cartwheel’s distinctive ring shape. This demonstrates the remarkable diversity of merger outcomes in our universe.
The difference between catastrophic restructuring and gentle perturbation often comes down to cosmic geometry—the precise angle at which two massive systems encounter each other.
The Dual Nature of Galactic Mergers
While collisions between galaxies compress gas and improve conditions for star formation, Webb reveals another side to this story: these encounters also disperse enormous amounts of gas across intergalactic space.
This creates a fundamental tension. The same process that triggers star birth in some regions can deprive other areas of the raw materials needed for stellar nurseries. It’s a cosmic balancing act, with creation and deprivation occurring simultaneously across these interacting systems.
The tenuous bridge connecting the two galaxies of Arp 107 represents this dual nature perfectly. It’s both a highway for material transfer between the galaxies and evidence of resources being drawn away from their original homes.
Seyfert Galaxies: Windows into Active Nuclei
The larger spiral galaxy in Arp 107 belongs to a special class known as Seyfert galaxies—one of the two largest groups of active galaxies (the other being quasars).
What makes Seyferts particularly valuable to astronomers is their relative proximity compared to distant quasars. Despite hosting actively feeding supermassive black holes at their centers, they’re close enough to study in detail, making them ideal laboratories for understanding the physics of active galactic nuclei.
In infrared light, Webb gives us an unprecedented look at the bright nucleus of Arp 107’s spiral component—a region dominated by that hungry supermassive black hole.
A Snapshot in Cosmic Time
What we’re seeing in Arp 107 is merely a single frame in an epic movie that will play out over hundreds of millions of years. The merger process has begun, but it’s far from complete.
Eventually, these two galaxies will fully coalesce, forming a single, larger system with properties determined by their combined histories. The “smile” that gives Arp 107 its distinctive appearance will fade, replaced by new structures born from the continued interaction.
This offers astronomers a valuable opportunity to study galaxy evolution in action. By comparing systems at different stages of merger, from initial approach to final coalescence, scientists can build a comprehensive picture of how galaxies grow and change throughout cosmic history.
Webb’s Revolutionary Infrared Vision
The James Webb Space Telescope’s ability to observe in infrared wavelengths is what makes these observations possible. Infrared light penetrates cosmic dust, revealing structures that would remain hidden in visible light.
This capability is particularly valuable when studying galactic mergers, which typically generate enormous quantities of dust through the compression and heating of interstellar material. Where optical telescopes might see only obscured, chaotic regions, Webb reveals the detailed dynamics of star formation and gas movement.
The combination of NIRCam and MIRI data in this image demonstrates the power of multi-wavelength observation. Different infrared bands highlight different physical processes, from stellar populations to actively forming stars to the distribution of complex organic molecules.
Beyond the Pretty Picture
While the aesthetic appeal of Webb’s images captivates public attention, their scientific value extends far deeper. Each pixel contains data that helps astronomers understand fundamental questions about cosmic evolution.
How do galaxies grow over time? What role do supermassive black holes play in galactic development? How efficiently can stars form in disturbed systems? Images like Arp 107 help scientists piece together these cosmic puzzles.
The study of interacting galaxies also provides context for understanding our own cosmic neighborhood. The Milky Way is on a collision course with the Andromeda galaxy, with the encounter expected in about 4.5 billion years. Systems like Arp 107 offer previews of what might await our galactic home.
A Universe in Motion
Perhaps the most profound lesson from Webb’s observations of Arp 107 is that the universe is fundamentally dynamic. Cosmic structures we might perceive as eternal are, in fact, ever-changing.
Galaxies aren’t isolated islands but participants in a cosmic ecosystem, influencing each other through gravity and exchanging material across the vastness of space. The universe we see today is just one moment in an ongoing process of evolution that has been unfolding since the Big Bang.
As Webb continues its mission, it will capture more of these cosmic interactions, building a comprehensive atlas of galactic collisions across cosmic time. Each new image adds another piece to our understanding of how the universe forms and evolves its most magnificent structures.
Arp 107, with its cosmic smile, reminds us that even in the apparent chaos of colliding galaxies, there is order and beauty—patterns that emerge from the fundamental physics governing our universe.
The Future of Arp 107
What will become of this smiling galaxy pair? Over the coming hundreds of millions of years, the two galaxies will continue their gravitational dance, drawing ever closer until they ultimately merge into a single system.
The supermassive black holes at their centers will eventually coalesce as well, releasing enormous energy in the process. New generations of stars will form from the compressed gas, while others will be flung to the system’s outskirts, creating extended halos of stellar populations.
The distinctive spiral structure will likely be lost, transformed into a more elliptical shape through the randomization of stellar orbits during the merger process. The “smile” that gives Arp 107 its charm is merely a temporary feature in its long cosmic evolution.
Yet even as this particular configuration fades, the system will continue to evolve, perhaps triggering new rounds of star formation or developing other distinctive structures. In the cosmic theater, the show never truly ends—it merely changes acts.
References
- NASA’s Webb Space Telescope (2024). Webb Provides Another Look Into Galactic Collisions. Retrieved from webbtelescope.org
- NASA’s Spitzer Space Telescope Archives (2005). Observations of Arp 107.
- Webb Science Writers’ Guide (2024). Understanding NIRCam and MIRI observations.
