Discovery of a Hypervelocity L Subdwarf at the Star/Brown Dwarf Mass Limit

August 2024 • 2024ApJ...971L..25B

Authors • Burgasser, Adam J. • Gerasimov, Roman • Kremer, Kyle • Brooks, Hunter • Alvarado, Efrain • Schneider, Adam C. • Meisner, Aaron M. • Theissen, Christopher A. • Softich, Emma • Karpoor, Preethi • Bickle, Thomas P. • Kabatnik, Martin • Rothermich, Austin • Caselden, Dan • Kirkpatrick, J. Davy • Faherty, Jacqueline K. • Casewell, Sarah L. • Kuchner, Marc J. • The Backyard Worlds: Planet 9 Collaboration

Abstract • We report the discovery of a high-velocity, very low-mass star or brown dwarf whose kinematics suggest it is unbound to the Milky Way. CWISE J124909.08+362116.0 was identified by citizen scientists in the Backyard Worlds: Planet 9 program as a high-proper-motion (μ = 0.″9 yr^‑1) faint red source. Moderate-resolution spectroscopy with Keck/NIRES reveals it to be a metal-poor early L subdwarf with a large radial velocity (‑103 ± 10 km s^‑1), and its estimated distance of 125 ± 8 pc yields a speed of 456 ± 27 km s^‑1 in the Galactic rest frame, near the local escape velocity for the Milky Way. We explore several potential scenarios for the origin of this source, including ejection from the Galactic center ≳3 Gyr in the past, survival as the mass donor companion to an exploded white dwarf, acceleration through a three-body interaction with a black hole binary in a globular cluster, and accretion from a Milky Way satellite system. CWISE J1249+3621 is the first hypervelocity very low-mass star or brown dwarf to be found and the nearest of all such systems. It may represent a broader population of very high-velocity, low-mass objects that have undergone extreme accelerations.

Links

• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2024ApJ...971L..25B
• PREPRINT http://arxiv.org/abs/2407.08578
• ELECTR https://doi.org/10.3847%2F2041-8213%2Fad6607