Binary mass ratio
= Binary mass ratio
{title2=$q=M_d/M_a$}
= Donor-to-accretor mass ratio
{synonym}
A binary <binary mass ratio> is the quotient of its component masses. For mass-transfer stability, specify the donor-to-accretor convention $q=M_d/M_a$ explicitly, since the inverse convention also occurs. Mass-ratio reversal changes which component is more massive.