Written by Ken Olum
The objects are
M31 Andromeda
Sun Sagittarius
Saturn Taurus
NGC 1313 Reticulum
Horsehead nebula Orion
Little dumbbell nebula Perseus
M13 Hercules
"no image available" Y (J, K, Q, W, X, Z would also be possible)
Trifid nebula Sagittarius
IC 5152 Indus
Antennae Corvus
Stingray nebula Ara
Mars Libra
There is no constellation that begins with Y. First letters spell the answer (astrophysical).