Chaotic dynamics of wide triples induced by galactic tides: a novel
  channel for producing compact binaries, mergers, and collisions
  Recent surveys show that wide ($>10^4$ AU) binaries and triples are abundant
in the field. We study the long-term evolution of wide hierarchical triple
systems and the role played by the Galactic tidal (GT) field. We find that when
the timescales of the secular von-Ziepel-Lidov-Kozai and the GT oscillations
are comparable, triple evolution becomes chaotic which leads to extreme
eccentricities. Consequently, the close pericentre approaches of the
inner-binary components lead to strong interactions, mergers and collisions. We
use a novel secular evolution code to quantify the key parameters and carry out
a population-synthesis study of low and intermediate-mass wide-orbit triples.
We find that in $\sim9\%$ of low-mass wide-triples the inner main-sequence
binaries collide or tidally-inspiral within $10\ \rm Gyr$, with direct
collisions are $6$ times more likely to occur. For the intermediate-mass
sample, $\sim7.6\%$ of the systems merge or inspiral with roughly equal
probabilities. We discuss the relative fractions of different stellar
merger/inspiral outcomes as a function of their evolutionary stage
(Main-Sequence, MS; Red-Giant, RG; or White-Dwarf, WD), their transient
electromagnetic signatures and the final products of the merger/inspiral. In
particular, the rate of WD-WD direct-collisions that lead to type-Ia Supernovae
is comparable to other dynamical channels and accounts for at most $0.1\%$ of
the observed rate. RG inspirals provide a novel channel for the formation of
eccentric common-envelope-evolution binaries. The catalysis of
mergers/collisions in triples due to GT could explain a significant fraction,
or even the vast majority, of blue-stragglers in the field, produce progenitors
for cataclysmic-variables, and give-rise to mergers/collisions of double-RG
binaries.
