Most massive stars are born in binaries (and sometimes triples, quadruples, and so on). As stars age, they grow larger in size by a hundred-fold or even thousand-fold expansion. When stars in binaries expand, parts of them approach the other star in the binary, whose gravity can then pull off the outer portions of the expanding star. The result is mass transfer from one star to the other.
Source:
https://phys.org/news/2020-06-stars-black-holes-cosmic-cloud.html