Discovery of a young stellar "snake" with two dissolving cores in the
  solar neighborhood
  We report the discovery of a young (only 30-40\,Myr) snake-like structure
(dubbed a stellar "snake") in the solar neighborhood from {\it Gaia} DR2. The
average distance of this structure is about 310\,pc from us. Both the length
and width are over 200\,pc, but the thickness is only about 80\,pc. The "snake"
has one tail and two dissolving cores, which can be clearly distinguished in
the 6D phase space. The whole structure includes thousands of members with a
total mass of larger than 2000\,$M_{\odot}$ in an uniform population. The
population is so young that it can not be well explained with the classical
theory of tidal tails. We therefore suspect that the "snake" is hierarchically
primordial, rather than the result of dynamically tidal stripping, even if the
"snake" is probably expanding. The coherent 5D phase information and the ages
suggest that the "snake" was probably born in the same environment as the
filamentary structure of Beccari et al.(2020). If so, the "snake" could extend
the sky region of the Vela OB2 association by a factor of $\sim 2$, and
supplement the census of its coeval structures. This finding is useful to
understand the history of the formation and evolution of the Vela OB2 complex.
The age of the "snake" well matches with that of the Gould Belt. In the sky
region of our interest, we detect one new open cluster, which is named as Tian
1 in this work.
