An isolated galaxy in the Local Void, NGC 6789, continues to form new stars despite lacking apparent gas fuel. New deeper images reveal no signs of mergers or gas inflows that could explain the phenomenon. The mystery of its star formation deepens, challenging astronomers' understanding of galactic evolution.
About 12 million light years away, in the direction of the Draco constellation, lies NGC 6789, a galaxy first discovered in 1883. Located in the sparsely populated Local Void, it is one of only a few galaxies in this empty region of space, making it extremely isolated compared to typical galaxies.
The galaxy is at least 1 billion years old, and over the past 600 million years, its core has formed new stars equivalent to about 100 million times the mass of the sun—roughly 4 percent of its total stellar mass. However, star formation requires gas as fuel, and the Local Void contains very little of it. By now, NGC 6789 should have depleted its original gas reserves.
Astronomers, led by Ignacio Trujillo at the Institute of Astrophysics of the Canary Islands, used the Two-meter Twin Telescope at Teide Observatory in Tenerife to capture deeper images of the galaxy. They sought evidence of events like a merger with another galaxy or an undetected gas stream that might have replenished its fuel without distorting its shape.
The observations showed no disturbances or irregularities in NGC 6789's structure. Possible explanations include leftover gas from the galaxy's formation or a tenuous nearby gas reservoir that did not alter its morphology. For now, the source of the star-forming fuel remains unsolved, adding to the puzzle of how isolated galaxies sustain activity in voids.
This finding, detailed in Research Notes of the AAS (DOI: 10.3847/2515-5172/ae1cbe), highlights the unexpected behaviors possible in the universe's emptiest regions.