During the 1960's, Pfleiderer and Siedentopf investigated
how spiral patterns in disk galaxies could be excited by gravitational
interactions between disk galaxies and concluded that chance
encounters between field galaxies are not sufficiently common enough
to produce the observed population of spirals. However, they did
produce, albeit in passing, the first plots of tail and bridge
building.
This was followed in the early 1970's by a spate of papers, but one
in particular stands out. Galactic Bridges and Tails by Toomre
and Toomre (1972) is seen as many as the seminal paper in the field of
galaxy interactions and mergers. Although it was not unusual at this
time for a paper to be published that dealt with computer modeling of
interacting galaxies, the publication of TT's paper was seen by many
as a key turning point in the theory of interacting galaxies,
triggering a true paradigm shift in the field. As will
be highlighted in the next section, Galactic Bridges and
Tails clearly established that bridges and tails - which for so long
were the source of much heated debate and disagreement - were
gravitational in nature. The paper comprehensively offered a very plausible
and natural means to produce these characteristic features of
interacting galaxies and indeed, through their discussion of related
phenomena in the final section, the Toomres inspired a burst of new
research. In particular, the discussion, Stoking the Furnace,
preempted Larson&Tinsley's 1978 paper which showed the connection
between starbursts and the merging of galaxies.