Imagine a galaxy perfectly isolated in the vastness of space, yet still actively forming new stars—that's the intriguing case of NGC 6789. This nearby dwarf galaxy, discovered over a century ago in 1883, is classified as a blue compact dwarf (BCD)—a small galaxy characterized by intense, centralized star formation and a compact, bright appearance. Situated approximately 12 million light-years away within the Local Void—a region notably scant in galaxies—NGC 6789's isolation is remarkable. Despite being cut off from significant galactic interactions, recent observations reveal that it continues to create stars in its core.
Prior studies estimated that about 4% of NGC 6789’s total stellar mass—roughly 100 million times that of our Sun—was formed within the last 600 million years. Interestingly, this youthful star activity occurs within a galaxy that exhibits an outer structure resembling an undisturbed, redder elliptical galaxy—an appearance typically associated with older, evolved stellar populations. This contrast raises a compelling question: What fuels the ongoing star formation in NGC 6789 when it seems so unperturbed and isolated?
To uncover the answer, a team led by Ignacio Trujillo from the University of La Laguna employed the advanced Two-meter Twin Telescope (TTT3) to capture deeper, more detailed optical images of NGC 6789 than ever before. Their goal was to explore the galaxy’s outer regions for faint features—such as delicate streams or signs of past minor mergers—that could have supplied the gas needed for star formation.
What they found, however, was surprising: the galaxy's elliptical shape persists even at extraordinarily low brightness levels—down to 30 magnitudes per square arcsecond in the g-band, extending out to about 1.5 arcminutes in radius—and there were no detectable tidal tails or remnants that would indicate a recent merger or interaction. This suggests the galaxy hasn't recently consumed a smaller satellite that could have triggered the starburst.
Furthermore, analysis allowed the researchers to estimate an upper limit of around 200,000 solar masses for any stars that might have been added through the disruption of a tiny satellite. Considering that the central starburst has formed approximately 4 million solar masses worth of new stars, the absence of stellar streams or debris strongly indicates that the ongoing star formation is likely driven by internal processes—either residual, or pristine gas that the galaxy has naturally accumulated.
The team concludes that NGC 6789’s recent star-forming activity probably results from the galaxy’s own stored-up gas or from the recent accretion of fresh, unprocessed gas from its surroundings—not from any external merger events. This insight challenges common assumptions about galaxy evolution, which often link star formation to galaxy interactions and mergers, especially in the universe’s crowded regions.
So, here's the twist: Could some isolated galaxies sustain star formation purely from internal reserves or external gas infall without the need for violent mergers? And how prevalent are these 'quiet' star factories in the universe? We invite you to share your thoughts and opinions—do you believe galaxy interactions are always necessary for star formation, or does NGC 6789 suggest a more peaceful universe? Dive into the discussion below!
This research was conducted with meticulous human effort, authored by Tomasz Nowakowski, edited by Gaby Clark, and reviewed by Robert Egan, emphasizing the importance of independent science journalism. If you find this kind of insightful science exploration valuable, consider supporting it with a donation—especially on a regular basis—to help keep independent research alive and accessible. Supporters can enjoy an ad-free experience as a thank you.
For those interested, further details are available in the original paper by Ignacio Trujillo and colleagues, published as a preprint on the arXiv server (2025). This ongoing conversation about isolated galaxy evolution continues to challenge and expand our understanding of the universe’s complexities—and your voice is an essential part of it.
