Astronomy Picture Of The Day: A Truly Extreme Binary System

 

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A Truly Extreme Binary System: ZTF J2020+5033This fascinating discovery from 2023 is indeed real and groundbreaking. The binary system ZTF J2020+5033, discovered using data from the Zwicky Transient Facility (ZTF), features a low-mass red dwarf star orbited by a high-mass brown dwarf in an astonishingly tight 1.9-hour period—the shortest known for any transiting brown dwarf by more than a factor of 7.Key details from the research:Distance: Approximately 445–457 light-years away (sources vary slightly due to measurement precision; Gaia data places it around 140 parsecs, or ~456 light-years). Components:Red dwarf: ~13.4% of the Sun's mass, ~17.6% of the Sun's radius, effective temperature ~2850 K. Brown dwarf: 80.1 Jupiter masses (near the upper limit for brown dwarfs, just below the hydrogen-burning threshold for stars), radius similar to Jupiter's (1.05 Jupiter radii), cooler at ~1700 K. The separation between the two is so small that the entire orbit fits well within the radius of our Sun—hence the dramatic "fits inside the Sun" description. The system is old (likely 5–13 billion years), with a thick-disk Galactic orbit and high tangential velocity, suggesting significant evolution. Researchers propose that the originally wider orbit has shrunk dramatically (by a factor of ~5 or more) due to magnetic braking: stellar winds coupled with the magnetic field carry away angular momentum, tightening the orbit over time. This process appears to remain efficient even in fully convective low-mass stars and brown dwarfs, challenging some evolutionary http://models.In the future (tens of millions to billions of years), the orbit will continue decaying. Eventually, the brown dwarf's stronger gravity may cause it to accrete material from the red dwarf, potentially pushing it over the mass threshold to become a low-mass star—or leading to more dramatic interactions.This rare eclipsing/transiting system provides a valuable laboratory for understanding brown dwarf formation, binary evolution, and magnetic dynamo processes in ultracool objects. The paper, led by Kareem El-Badry and published in The Open Journal of Astrophysics , highlights how such close low-mass binaries may be more common than thought, with upcoming surveys likely uncovering more.A remarkable peek into the extremes of stellar (and substellar) companionship!