A research team, led by astronomers from National Astronomical Observatories of Chinese Academy of Sciences (NAOC), has discovered 591 high velocity stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and Gaia, and 43 of them can even escape from the Galaxy. After the first high velocity star was discovered in 2005, there are in total of over 550 high velocity stars have been found with multiple telescopes in 15 years. “The 591 high velocity stars discovered this time doubled the total number of high velocity stars previously discovered, bringing the total number exceeding 1000,” said Dr. Yin-Bi Li, the lead author of the research.

High velocity stars are kind of fast-moving stars, and they can even escape from the Galaxy. “Though rare in the Milky Way, high velocity stars, with unique kinematics, can provide deep insight into a wide range of Galactic science, from the central supermassive black hole to distant Galactic halo,” said Prof. You-Jun Lu from NAOC, co-author of this research.

As mentioned above, these high velocity stars were discovered with LAMOST and Gaia. LAMOST is the largest optical telescope in China, which has the highest spectral acquisition rate in the world and can observe about 4,000 celestial targets in one single exposure, and it began the regular surveys in 2012, which established the largest spectra database in the world. Gaia is a space-based mission in the science program of the European Space Agency (ESA) launched in 2013, and it provided astrometric parameters for over 1.3 billion sources, which is the largest database of astrometric parameters. “The two massive databases provide us unprecedented opportunity to find more high velocity stars, and we did it,” said Prof. A-Li Luo from NAOC, co-author of this research.

From the kinematics and chemistries, research team found that the 591 high velocity stars are inner halo stars. “Their low metallicities indicate that the bulk of the stellar halo formed as a consequence of the accretion and tidal disruption of dwarf galaxies,” said Prof. Gang Zhao from NAOC, co-author of this research.

The discovery of these high velocity stars tells us that the combination of multiple large surveys in the future will help us to discover more high velocity stars and other rare stars, which will be used to study the unsolved mystery about our Galaxy.

This work has been recently published online in The Astrophysical Journal Supplement Series, and can be accessed at https://iopscience.iop.org/article/10.3847/1538-4365/abc16e.

Figure: 591 high velocity stars’ positions and orbits (Credit: Kong Xiao of NAOC)