Page last updated Jul 11, 2016|
A magnitude 14(?) spiral galaxy (type (R)Sa? pec) in Hercules (RA 16 02 16.7, Dec +42 55 01)
Physical Information: Based on a recessional velocity of 7340 km/sec, a straightforward calculation indicates that PGC 56779 is about 325 to 330 million light years away (using H = 73 km/sec/Mpc). However, for objects at such distances we should take into account the expansion of the Universe during the time it took their light to reach us. Doing that shows that the galaxy was about 315 to 320 million light years away at the time the light by which we see it was emitted, about 320 to 325 million years ago (the difference between the two numbers being due to the expansion of the intervening space during the light-travel time). Given that and its apparent size of about 1.5 by 1.4 arcmin, the galaxy is about 145 to 150 thousand light years across. PGC 56779 is a starburst galaxy, which is unusual because it is a "field" galaxy, apparently far from any neighbros, and starburst formation is thought to be usually caused by the collision or passage of nearby galaxies, so the cause of its activity is a mystery.
Above, a 12 arcmin wide SDSS image centered on PGC 56779
Below, a 1.6 arcmin wide HST image of the galaxy (Image Credit ESA/Hubble/& NASA and N. Grogin (STScI))
PGC 56938 (with PGC 56953 = Arp 101)
A 15th-magnitude lenticular galaxy (type E/S0?) in Serpens (RA 16 04 28.2, Dec +14 46 57)
Apparent size about 1.4 by 0.9 arcmin. Used in the Arp Atlas as an example of a spiral galaxy (PGC 56953
, which see for images) with an elliptical companion.
PGC 56953 (with PGC 56938 = Arp 101)
A 14th-magnitude spiral galaxy (type S0/a? pec) in Serpens (RA 16 04 31.8, Dec +14 49 08)
Apparent size about 3.0 by 0.5 arcmin. Used in the Arp Atlas as an example of a spiral galaxy with an elliptical companion (PGC 56938
Above, a 3 by 6 arcmin wide closeup of PGC 56953 and PGC 56938
Below, a 12 arcmin wide region centered on the pair