WISE 0535−7500

Lore & Background

WISE 0535−7500 was discovered in 2012 by J. Davy Kirkpatrick et al. from data collected by the Wide-field Infrared Survey Explorer (WISE) Earth-orbiting satellite, a NASA infrared-wavelength 40 cm space telescope whose mission lasted from December 2009 to February 2011. In 2012 Kirkpatrick et al. published a paper in The Astrophysical Journal presenting seven new Y-type brown dwarfs found by WISE, among which was WISE 0535−7500.

In 2014 it was found that WISE 0535 is more luminous than predicted by atmospheric models. In 2016 it was suggested that such overluminosity could be explained if it is a binary system of similar components. Close imaging has not revealed any companions within detection capacities, implying that the separation between the components is less than 1.9 astronomical units. One 2024 study found that while the overluminosity could be reasonably explained by a metal-poor atmosphere, an unresolved binary system is a better possibility. The primary was estimated to have a mass and an effective temperature of 450 K, the secondary a mass and an effective temperature of 350 K, with a system age of 5 Gyr. A 2026 study found that the overluminosity can be explained by either binarity or a high surface gravity with or without a metal-poor atmosphere; the components would have temperatures of 480 K and 340 K with near-solar metallicity. For the case that WISE 0535 is a single star, a mass, a radius and an effective temperature of 395 K have been measured.

WISE 0535−7500 was studied with JWST by Beiler et al. in 2024 together with 22 other late-T and Y-dwarfs. It stands out due to having no discernable CO₂ band and an almost undetectable CO band, possibly due to low metallicity or high surface gravity. These features make the object extremely red in Spitzer colors. It also showed stronger NH₃ absorption compared to objects of the same temperature. Other common prominent features like H₂O and CH₄ are present in its spectrum, but like other late-T and Y-dwarfs it is missing PH₃, which is predicted to occur for these objects.

Reader's Guide

WISE 0535−7500 is significant as a possible binary system of two Y1-class brown dwarfs, a rare configuration among the coolest known substellar objects. Its overluminosity relative to atmospheric models has made it a test case for understanding the physical properties of Y dwarfs, with studies exploring whether the excess light arises from unresolved binarity, metal-poor composition, or high surface gravity. The object's unusual spectral features—including missing CO₂ and CO bands, strong NH₃ absorption, and extreme redness in Spitzer colors—further challenge current atmospheric models and highlight the diversity among Y dwarfs. Its study with JWST in 2024, alongside other late-T and Y dwarfs, has provided high-quality spectra that help refine the understanding of chemical processes in the coldest brown dwarfs. The ongoing uncertainty about its binary nature and the range of possible explanations for its properties underscore the complexity of characterizing the lowest-mass and coolest members of the stellar and substellar population. WISE 0535−7500 thus serves as a benchmark object for future observations and modeling of Y dwarfs, particularly in the context of binary frequency and atmospheric physics at temperatures below 500 K.

Did You Know?

• It was discovered in 2012 from data collected by the WISE space telescope.
• The system has an estimated age of 5 Gyr.