The ZTF J0440+2325 system brings together a red dwarf and a brown dwarf. The latter is more massive than a giant planet, but too light to initiate a true fusion reaction and become a genuine star. This type of object is informally described as a “failed star.” The two are so close that they complete one full orbit around each other in just 86.65 minutes.
The red dwarf has about 85 times Jupiter’s mass. Its companion has about 25 times Jupiter’s mass. Their entire orbit could fit inside the diameter of the Sun, placing the star and the brown dwarf in extreme proximity. The red dwarf’s gravity then distorts the brown dwarf. Some of its gas flows toward the star in the form of a continuous stream.
This gas does not fall discreetly onto the red dwarf. When it strikes its surface, it creates a much hotter and brighter region. Regular variations in this zone over the course of the orbit helped researchers reconstruct how matter moves between the two objects.
This type of transfer is often observed when a black hole, neutron star, or white dwarf draws in a companion. Here, the object receiving the matter is an ordinary star of very low mass. Such a situation had never before been observed directly in this way.
The most surprising aspect is the slowness of the process. Models indicate that the transfer can remain stable instead of running away. The brown dwarf would therefore not be swallowed quickly: it could gradually lose its matter over billions of years.
This discovery adds a possible new fate for objects located very close to their star. A planet or brown dwarf does not necessarily have to be swallowed all at once. Under certain conditions, it can be consumed very slowly, layer by layer.
The researchers also identified a second system, ZTF J1444+4820, whose period is only 67 minutes and which could operate in a comparable way. Further searches of sky surveys will determine whether these tight pairs are rare or simply difficult to identify.