SDSS 1557 (full designation SDSS J155720.77+091624.6) is a binary star system located approximately 1,000 light-years from Earth. The system consists of a low-mass white dwarf and a brown dwarf orbiting each other with an orbital period of approximately 2.27 hours.
The system is notable in the field of astrophysics for being the first confirmed instance of a binary star system where a white dwarf is actively being "polluted" by a circumbinary disk of rocky debris. In 2017, researchers reported that the atmosphere of the white dwarf exhibited high concentrations of heavy elements, specifically silicon and magnesium. The presence of these elements indicates that the star is accreting material from a surrounding disk of planetary or asteroidal fragments.
The discovery of SDSS 1557 is significant because it provides empirical evidence that rocky material can form and survive in the complex gravitational environment of a binary system. Prior to this discovery, such debris disks—which are remnants of planetary systems—had been observed almost exclusively around single stars. The composition of the debris in SDSS 1557 suggests that the material is predominantly rocky rather than icy, indicating that terrestrial-like planetesimals can originate in close-binary systems.
The system was identified using data from the Sloan Digital Sky Survey (SDSS), with follow-up observations conducted using the Very Large Telescope (VLT) and the Gemini Observatory. Studies of SDSS 1557 contribute to the scientific understanding of planetary evolution and the ultimate fate of solar systems involving multiple stars.