Discovery of a Hypervelocity L Subdwarf at the Star/Brown Dwarf Mass Limit
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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 2024
- DOI:
- 10.3847/2041-8213/ad6607
- arXiv:
- arXiv:2407.08578
- Bibcode:
- 2024ApJ...971L..25B
- Keywords:
-
- Globular star clusters;
- Hypervelocity stars;
- L subdwarfs;
- Metallicity;
- Type Ia supernovae;
- Low mass stars;
- Galactic archaeology;
- 656;
- 776;
- 896;
- 1031;
- 1728;
- 2050;
- 2178;
- Astrophysics - Solar and Stellar Astrophysics;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 17 pages, 3 figures, accepted for publication in Astrophysical Journal Letters