The image below shows two views of the interacting
pair of galaxies (113704.8+321108.9 is the galaxy in the
upper left; 113707.1+321227.2 is the galaxy in the lower
right). The image on the
left is in ultraviolet light and shows bright rings and
knots where luminous blue stars have recently formed.
The image on the right is in infrared light and shows
radiation from older, red stars.
We use these images - the relative amount of blue
and red light from various parts of each galaxy - to
infer the rate that new stars form and how they evolve
with time. You can see that the ring of star formation
in the upper galaxy is bright in both images, which
indicates that the newly-formed stars are associated
with hot dust leftover from the burst of star formation.
The other galaxy has no bright ring in the infrared image,
so it has no dust.