The interactive plot above shows the distribution of stars with a co-moving neighbor in the Solar neighborhood in a cylindrical projection onto the Galactic plane.
We looked for these co-moving pairs of stars using the Tycho-Gaia Astrometric Solution (TGAS) which is released as a part of the Gaia first data release. Gaia is an exciting and ambitious space mission launched in 2013 to chart distances and proper motions of one billion stars in our Galaxy, the Milky Way.
Using the positions (including distances) and proper motions of two million stars,
and their uncertainties,
in the TGAS, we perform a marginalized likelihood ratio
test to pick out pairs
that are consistent with having the same 3D velocity. Of about 270,000 pairs that
we examine, we find ~13,000 candidate co-moving pairs. Some of these pairs are
connected by sharing a co-moving neighbor to form a
As you can see, some of the larger connected components nicely coincide with the positions of
known star clusters. An aggregate of co-moving pairs on
the upper right corresponds to
positions of known OB associations e.g., Scorpius-Centaurus Association.
There are also many candidate co-moving pairs which are mutually exclusively linked. These are found with very wide separations upto 10 pc, our search limit. But we only show the hundred largest groups here for speed. For more details, see a our paper on arxiv.