Brown dwarfs are often called “failed stars” because they are too small to keep nuclear fusion going in their cores, the process that makes stars shine.
These objects sit somewhere between planets and stars, with masses about 13 to 80 times that of Jupiter. Because they cannot sustain fusion, they are usually faint, cool, and easy to overlook in the night sky.
But a new discovery shows that brown dwarfs may not be as “failed” as we once thought.
Scientists at Caltech have found a pair of brown dwarfs behaving in a remarkable way—so remarkable that together, they may eventually create a real star.
The researchers made this discovery by studying data from the Zwicky Transient Facility (ZTF), a powerful survey telescope at Palomar Observatory in California.
By examining changes in brightness across billions of objects, they identified one unusual system that brightened and dimmed every 57 minutes.
This object, named ZTF J1239+8347, turned out to be two brown dwarfs orbiting extremely close to each other—so close that the entire system could fit within the distance between Earth and the Moon.
Located about 1,000 light-years away in the constellation Ursa Major, these two objects are locked in a tight dance, circling each other once every hour.
What makes this pair truly special is what happens between them. One of the brown dwarfs is pulling material from the other. As gas flows from the smaller, less dense object onto its partner, it forms a bright, hot region on the surface. This hotspot glows in blue and ultraviolet light and rotates in and out of view as the pair orbits, causing the regular changes in brightness detected by the telescope.
This kind of mass transfer is well known in larger systems, such as pairs of white dwarfs, which are the dense remains of stars like our Sun. However, it has never been observed before in brown dwarfs, making this discovery the first of its kind.
Scientists are still unsure how the two brown dwarfs ended up so close together. One possibility is that a third star once influenced their motion, pushing them into a tighter orbit. Over time, their gravitational pull would have brought them even closer, eventually allowing one to start feeding off the other.
The most exciting part is what may happen next. As one brown dwarf gains more mass, it could eventually become heavy enough to start nuclear fusion—essentially turning into a true star. Alternatively, the two objects may merge into a single, brighter star. In either case, two dim, “failed” stars could combine to create something much more powerful.
This discovery suggests that such systems might be more common than scientists once thought. With new telescopes like the Vera Rubin Observatory expected to come online soon, researchers hope to find many more examples. These unusual pairs could help us better understand how stars form—and how even the faintest objects in space can get a second chance to shine.
Source: California Institute of Technology.
