  Habitable zones are regions around stars where large bodies of liquid water
can be sustained on a planet or satellite. As many stars form in binary systems
with non-zero eccentricity, the habitable zones around the component stars of
the binary can overlap and be enlarged when the two stars are at periastron
(and less often when the stars are at apastron). We perform N-body simulations
of the evolution of dense star-forming regions and show that binary systems
where the component stars originally have distinct habitable zones can undergo
interactions that push the stars closer together, causing the habitable zones
to merge and become enlarged. Occasionally, overlapping habitable zones can
occur if the component stars move further apart, but the binary becomes more
eccentric. Enlargement of habitable zones happens to 1-2 binaries from an
average initial total of 352 in each simulated star-forming region, and
demonstrates that dense star-forming regions are not always hostile
environments for planet formation and evolution.
