Origin of a Massive Hyper-runaway Subgiant Star LAMOST-HVS1: Implication from Gaia and Follow-up Spectroscopy
Abstract
We report that LAMOST-HVS1 is a massive hyper-runaway subgiant star with a mass of 8.3 {M}⊙ and super-solar metallicity, which was ejected from the inner stellar disk of the Milky Way ∼33 {Myr} ago with the intrinsic ejection velocity of {568}-17+19 {km} {{{s}}}-1 (corrected for the streaming motion of the disk), based on the proper motion data from Gaia Data Release 2 (DR2) and high-resolution spectroscopy. The extremely large ejection velocity indicates that this star was not ejected by the supernova explosion of a binary companion. Rather, it was probably ejected by a three- or four-body dynamical interaction with more massive objects in a high-density environment. Such a high-density environment may be attained at the core region of a young massive cluster (YMC) with mass of ≳104 {M}⊙ . The ejection agent that took part in the ejection of LAMOST-HVS1 may be an intermediate mass black hole (≳100 {M}⊙ ), a very massive star (≳100 {M}⊙ ), or multiple ordinary massive stars (≳30 {M}⊙ ). Based on the flight time and the ejection location of LAMOST-HVS1, we argue that its ejection agent or its natal star cluster is currently located near the Norma spiral arm. The natal star cluster of LAMOST-HVS1 may be an undiscovered YMC near the Norma spiral arm.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 2019
- DOI:
- 10.3847/1538-4357/ab05c8
- arXiv:
- arXiv:1810.02029
- Bibcode:
- 2019ApJ...873..116H
- Keywords:
-
- Galaxy: disk;
- Galaxy: kinematics and dynamics;
- open clusters and associations: general;
- stars: abundances;
- stars: early-type;
- stars: individual: LAMOST-HVS1;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- Minor revision after referee's comments (conclusion unchanged). ApJ submitted. 23 pages. 7 figures. 2 tables. Predicted location of IMBH (or the undiscovered young massive cluster) in the Milky Way is shown in Fig 7. High-resolution spectra (Magellan/MIKE) can be distributed upon request. Comments welcome