A remarkable binary system, known as ZTF J2020+5033, has recently been uncovered with astonishing characteristics. This extraordinary discovery has left scientists astounded as it presents a rotational tightness that allows both objects to snugly fit inside the Sun. Located a mere 457 light-years away, this intriguing system consists of a high-mass brown dwarf and a low-mass red dwarf that orbit each other on an incredibly swift 1.9-hour loop. In terms of proximity, this binary system is approximately one-seventh the distance between any previously discovered brown dwarf and its orbiting counterpart, making it an unparalleled finding. By demonstrating a distance less than half the radius of the Sun, ZTF J2020+5033 may reveal valuable insights into the mysterious nature of brown dwarf and small star companionship.
In the vast expanse of the cosmos, few instances of brown dwarfs coexisting in close binaries with other diminutive stars have been observed. A team of researchers, led by astrophysicist Kareem El-Badry from the Harvard-Smithsonian Center for Astrophysics, has proposed that the study of ZTF J2020+5033 could hold the key to unraveling this enigmatic phenomenon. The team’s findings have been submitted to The Open Journal of Astrophysics and are available on the preprint server arXiv.
Brown dwarfs, occupying a unique space between minuscule stars and massive planets, do not precisely adhere to the definition of conventional stars. Ranging from 13 to 80 times the mass of Jupiter, these celestial entities possess sufficient mass to ignite deuterium fusion in their cores but lack the necessary amount to sustain hydrogen fusion, which powers full-fledged stars. Due to their small size and faint luminosity, detecting brown dwarfs poses considerable challenges. Presently, only approximately 5,000 brown dwarfs have been identified within the Milky Way, with the majority of them existing in isolation. Merely 1 percent of stars similar in mass to the Sun and smaller are part of binaries with brown dwarfs within a few astronomical units. However, astronomers actively pursue these binaries to gain insights into the properties, formation, and evolution of brown dwarfs through interactions with companion stars.
In their quest to identify low-mass binaries likely to harbor brown dwarfs, El-Badry and his team employed the Zwicky Transient Facility and discovered the fascinating ZTF J2020+5033 system. By conducting follow-up studies, including the examination of data collected by Gaia, they obtained precise measurements and confirmed the system’s characteristics. The red dwarf within this binary is relatively undersized, measuring a mere 17.6 percent of the Sun’s radius and 13.4 percent of its mass. Conversely, the brown dwarf teeters at the upper mass threshold for these enigmatic entities, possessing a similar radius to Jupiter but a staggering mass 80.1 times that of the largest planet in our solar system.
Beyond their remarkable composition, ZTF J2020+5033’s age poses a series of intriguing questions. The system’s antiquity suggests that both objects were once considerably larger, pointing towards their initial separation distance being at least five times greater than their current proximity. The escape of material from the star becomes decelerated by the star’s magnetic field at a significant distance before eventually escaping. Analogous to a spinning ice skater slowing down by extending their arms, mass distribution within the system slows the star’s rotation, thereby causing the binary’s orbit to shrink. Remarkably, the tight orbit of this binary system demonstrates the efficiency of this “magnetic braking” phenomenon, even in low-mass stars and brown dwarfs.
With ZTF J2020+5033’s orbital decay process in progress, scientists anticipate further shrinking in the future. Despite being smaller and less massive than its red dwarf companion, the brown dwarf boasts slightly higher surface gravity. Consequently, as both objects draw closer to one another, the brown dwarf will eventually begin extracting material from the red dwarf. If magnetic braking indeed influences the decaying orbit, mass transfer should commence within several tens of millions of years. While humanity will not witness this astonishing phenomenon, the discovery of such a nearby system implies the relatively common existence of these closely bound, low-mass binaries. The scarcity of previous observations can be attributed to the dimness of these celestial entities. Luckily, advancements in telescope technology offer the potential to unveil more of these binaries, empowering scientists to conduct comprehensive investigations into the intricacies of magnetic braking in low-mass stars.
The unparalleled discovery of the ZTF J2020+5033 binary system pushes the boundaries of astronomical knowledge. This incredible finding not only showcases the tightest orbit of a brown dwarf but also sheds light on the formation and dynamics of brown dwarf binaries. With further exploration and technological advancements, the study of these elusive celestial phenomena promises to unlock the mysteries of our fascinating universe.