Discovery of a Candidate Hypervelocity Star Originating from the Sagittarius Dwarf Spheroidal Galaxy
Yang Huang, Qingzheng Li, Huawei Zhang, Xinyi Li, Weixiang Sun, Jiang Chang, Xiaobo Dong, Xiaowei Liu
Abstract
Abstract In this Letter, we report the discovery of an intriguing hypervelocity star (HVS; J1443+1453) candidate that is probably from the Sagittarius Dwarf Spheroidal galaxy (Sgr dSph). The star is an old and very metal-poor low-mass main-sequence turn-off star (age ∼14.0 Gyr and [Fe/H] = −2.23 dex) and has a total velocity of km s −1 in the Galactic rest frame and a heliocentric distance of kpc. The velocity of J1443+1453 is larger than the escape speed at its position, suggesting that it is a promising HVS candidate. By reconstructing its trajectory in the Galactic potential, we find that the orbit of J1443+1453 intersects closely with that of Sgr dSph Myr ago, when the latter has its latest pericentric passage through the Milky Way. The encounter occurs at a distance kpc from the center of Sgr dSph, a distance that is smaller than the size of the Sgr dSph. The chemical properties of this star are also consistent with those of an Sgr dSph-associated globular cluster, or of the Sgr stream member stars. Our finding suggests that J1443+1453 is an HVS that is either tidally stripped from the Sgr dSph or ejected from the Sgr dSph by the gravitational slingshot effect, requiring a (central) massive/intermediate-mass black hole or a (central) massive primordial black hole in the Sgr dSph.