Astronomers have made a groundbreaking discovery of a binary system with a rotation so tight that both objects could comfortably fit inside the Sun. Named ZTF J2020+5033, this system is located just 457 light-years away and consists of a high-mass brown dwarf and a low-mass red dwarf that orbit each other every 1.9 hours. This is the closest orbit a brown dwarf has been found in, making the distance between the two objects less than half the radius of the Sun.
The rarity of brown dwarfs in close binaries with other small stars makes ZTF J2020+5033 an intriguing find. Astrophysicist Kareem El-Badry of the Harvard-Smithsonian Center for Astrophysics, who led the team behind the discovery, believes that this system could provide valuable insights into why such binaries are so uncommon.
The research, which has been submitted to The Open Journal of Astrophysics and is available on the preprint server arXiv, sheds light on the nature of brown dwarfs. These objects fall between the classification of stars and planets, with masses ranging from 13 to 80 times that of Jupiter. While they are massive enough to ignite fusion of deuterium in their cores, they lack the necessary mass to sustain hydrogen fusion like full stars.
Due to their small size and dimness, brown dwarfs are challenging to detect. Currently, around 5,000 brown dwarfs have been identified in the Milky Way, with the majority existing in isolation. Only about 1 percent of Sun-like and lower mass stars are found in binaries with brown dwarfs within a few astronomical units.
However, astronomers are actively searching for these binaries as they can provide valuable information about the properties, formation, and evolution of brown dwarfs. Using the Zwicky Transient Facility, El-Badry and his team discovered ZTF J2020+5033 and conducted follow-up studies using various datasets, including data from Gaia, to confirm its characteristics.
The red dwarf in the system is relatively small, with only 17.6 percent of the radius and 13.4 percent of the mass of the Sun. On the other hand, the brown dwarf is on the upper mass limit for these enigmatic objects, with a radius similar to Jupiter but 80.1 times its mass.
The age of both objects raises questions about their formation and evolution. El-Badry and his colleagues suggest that the brown dwarf and red dwarf were once considerably larger and were at least five times more distant from each other.
The researchers propose that the star’s magnetic field plays a role in the shrinking orbit of the binary system. When material from the star escapes, it is slowed down by the star’s magnetic field before finally escaping. This process, known as “magnetic braking,” is similar to how a spinning ice skater slows down by extending their arms. The tight orbit in 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 shrinking in the future. Although the brown dwarf is smaller and less massive than the red dwarf, it has slightly higher surface gravity, which will cause it to start stealing material from the red dwarf as they draw closer together.
If magnetic braking is indeed responsible for the decaying orbit, mass transfer between the two objects is expected to begin within a few tens of millions of years. While we won’t be around to witness this event, the discovery of ZTF J2020+5033 suggests that close low-mass binaries like this are relatively common, but their dimness has made them difficult to detect.
However, advancements in telescope technology may soon allow scientists to identify more of these systems, enabling a more comprehensive study of magnetic braking in tiny stars.
The research conducted by El-Badry and his team provides valuable insights into the nature of brown dwarfs and their interactions with companion stars. By studying systems like ZTF J2020+5033, astronomers can deepen their understanding of these enigmatic objects and their place in the universe.
How did ZTF J2020+5033 remain in such a tight orbit without merging?
Times more massive. The tight orbit of the system suggests that it likely formed through a different mechanism than other brown dwarf binaries.
The researchers believe that ZTF J2020+5033 may have formed from the fragmentation of a collapsing molecular cloud core, a process that can produce both low-mass stars and brown dwarfs. However, the extreme proximity of the two objects raises questions about how they were able to remain in such a tight orbit without merging.
Further observations of this binary system, as well as additional discoveries of similar systems, could provide important clues about the formation and evolution of brown dwarfs. Understanding their origins and properties is not only important for our understanding of stellar evolution, but also for the search for potentially habitable exoplanets. Brown dwarfs can influence the habitability of nearby planets, so studying their interactions with other objects in binary systems is crucial.
In conclusion, the discovery of ZTF J2020+5033 opens up new possibilities for studying the fascinating world of brown dwarfs. Its close orbit with a red dwarf provides a unique opportunity to investigate the dynamics and formation of these enigmatic objects. As astronomers continue to explore the cosmos, they hope to uncover more of these rare systems and unravel the mysteries that lie within them.
This mind-boggling discovery pushes the boundaries of what we thought was possible in the universe. A binary system with such an incredibly tight rotation, even the objects inside are smaller than the sun itself! The wonders of astrophysics never cease to amaze.