2026-03-18 カリフォルニア工科大学（Caltech）
Researchers have spotted a very tight-knit pair of brown dwarfs, named ZTF J1239+8347, in which one is actively siphoning material from the other, as depicted in this artist’s illustration. Ultimately, the brown dwarfs are expected to merge to form a new star; alternatively, the brown dwarf gaining the extra mass will ignite to become a star. Either way, a pair of failed stars will have created a brilliant new star.Credit: Caltech/R. Hurt (IPAC)
＜関連情報＞
- https://www.caltech.edu/about/news/how-two-dim-stars-came-together-to-shine-brightly
- https://iopscience.iop.org/article/10.3847/2041-8213/ae486e
質量移動を行う褐色矮星連星系が57分周期で公転している A Mass Transferring Brown Dwarf Binary on a 57 Minute Orbit
Samuel Whitebook, Antonio C. Rodriguez, Kevin Burdge, Thomas Prince, Dimitri Mawet, Sam Rose, Pablo Rodríguez-Gil, Anica Ancheta, Ariana Pearson, Sage Santomenna,…
The Astrophysical Journal Letters Published: 2026 March 18
DOI:10.3847/2041-8213/ae486e
Abstract
Mass transfer in stellar binaries has been well studied in most stellar mass ranges, with the notable exception of ultracool stars and substellar brown dwarfs. We report the discovery of ZTF J1239+8347 with the Zwicky Transient Facility (ZTF), a brown dwarf binary currently undergoing stable mass transfer with an orbital period of 57.41 minutes. Optical time-series photometry reveals an extremely high amplitude (>2 magnitude peak-to-trough) variability at short wavelengths, indicative of an orbiting hot spot slightly buried inside the atmosphere of the accretor. We use parallax measurements from Gaia along with optical and near-infrared spectra to infer an accretion temperature of Teff = 8904 ± 54 K, an atmospheric temperature of the accretor of Tatmo ≈ 1500 K, and a slightly inflated accretor radius of Racc =1.20+0.15-0.11 RJup. ZTF J1239+8347 is a direct impact accretor, typically only seen in double degenerate white dwarf binaries, which are approximately a million times denser than the components in ZTF J1239+8347. The existence of an accreting brown dwarf binary suggests that angular momentum loss can be strong enough to make ultracool binaries interact in a Hubble time. The observed faintness (∼20 mag) and relative proximity (≈300 pc) of ZTF J1239+8347 suggest that many similar systems are likely to be found by the upcoming Rubin Observatory Legacy Survey of Space and Time.
