Dr. Paula Jofre, an astronomer from the University of Cambridge, and a team picked 22 stars (including our sun) and observed their chemical makeup, their age, and their movement to plot them on a stellar "tree of life."
They found that the stars they looked at could be plotted on three branches of the tree, with a few miscellaneous ones that didn't fit with the others.
They can tell which stars are related based on their chemical makeup, almost like their stellar DNA. If they were born in the same gas cloud then their makeup will be similar.
This study found 8 of stars they looked at were the sun's siblings. The researchers also suggested some of the stars may have originated from another galaxy that was absorbed by the Milky Way.
University of Cambridge: Mapping the family tree of stars
New Scientist: Family tree of stars helps reconstruct Milky Way's formation
Monthly Notices of the Royal Astronomical Society: Cosmic phylogeny: reconstructing the chemical history of the solar neighbourhood with an evolutionary tree