Record-Breaking Binary System Found with Incredibly Tight Rotation
Astronomers have made a groundbreaking discovery of a record-breaking binary system with an unprecedentedly tight rotation. This extraordinary binary system, named ZTF J2020+5033, is located just 457 light-years away and consists of a high-mass brown dwarf and a low-mass red dwarf. These two objects orbit each other at an astonishingly fast rate of 1.9 hours. In fact, this close orbit is over seven times nearer than any other brown dwarf system previously found, making the distance between the two objects less than half the radius of our own Sun.
The finding of brown dwarfs in close binaries is a rarity in the field of astronomy. The discovery of ZTF J2020+5033 could potentially shed light on the reasons for this scarcity. A team of astrophysicists led by Kareem El-Badry from the Harvard-Smithsonian Center for Astrophysics believes that studying this binary system could provide valuable insights into the formation and evolution of brown dwarfs. Their research has been submitted to The Open Journal of Astrophysics and is available on the preprint server arXiv.
Brown dwarfs are not officially classified as stars, as they exist in a gray area between small stars and massive planets. With a mass ranging between 13 and 80 times that of Jupiter, brown dwarfs are too massive to be considered planets but lack the necessary hydrogen fusion to sustain full stellar ignition like stars.
Due to their small size and dimness, brown dwarfs are challenging to detect. Currently, only around 5,000 brown dwarfs have been identified in the Milky Way, with the majority being solitary objects. The occurrence of brown dwarfs in binary systems with other stars is rare, with only about 1 percent of Sun-like and lower mass stars found in such pairs within a few astronomical units.
Despite their elusiveness, astronomers actively search for these binary systems. Paired brown dwarfs that interact with companion stars provide valuable research opportunities to measure their properties and gain a better understanding of their origin and development.
El-Badry and his team utilized the Zwicky Transient Facility to search for low-mass binaries potentially including a brown dwarf, leading to the discovery of ZTF J2020+5033. Follow-up observations using various datasets, including data from the Gaia mission, allowed the researchers to obtain precise measurements and confirm the system’s characteristics.
The red dwarf in the binary system is relatively small, with only 17.6 percent of the radius and 13.4 percent of the mass of our Sun. The brown dwarf, however, teeters on the upper mass limit for these enigmatic objects. It has a radius similar to that of Jupiter but is a staggering 80.1 times more massive.
Other features of the system suggest that both objects are quite old, raising questions about their formation and subsequent journey. El-Badry and his team propose that the objects were once considerably larger than their present state, indicating they were once at least five times farther apart from each other.
The researchers believe that the phenomenon of “magnetic braking,” which slows the spin of a star, plays a role in shrinking the orbit of binary systems. Just as an ice skater slows down by extending their arms, the mass distribution resulting from magnetic braking slows the star’s rotation, thus reducing the size of the orbit in binary systems. The tight orbit of ZTF J2020+5033 suggests that magnetic braking is an efficient process, even in low-mass stars and brown dwarfs.
As a result, the orbit of ZTF J2020+5033 is expected to continue to shrink in the future. Despite being smaller and less massive than the red dwarf, the brown dwarf possesses a slightly higher surface gravity, meaning that it will eventually start absorbing material from its companion as they draw closer together.
If magnetic braking is, indeed, responsible for the decaying orbit, this mass transfer is anticipated to initiate within tens of millions of years. Although we won’t be around to witness this event, the discovery of ZTF J2020+5033, located in close proximity to our own Solar System, suggests that these close low-mass binary systems are rather common; we may have just detected few due to their dimness.
However, with advancements in telescope technology, scientists hope to uncover more of these systems in the near future, enabling a comprehensive study of the effects of magnetic braking in small stars.
The research conducted by El-Badry and his colleagues has significant implications for our understanding of binary systems and provides crucial insights into the mysterious world of brown dwarfs. Their work explores the fundamental mechanisms behind the formation, evolution, and interactions of objects within these unique celestial configurations.