Celestial Atlas
PGC 18000 - 18499 ←     PGC Objects: PGC 18500 - 18999 Link for sharing this page on Facebook     → PGC 19000 - 19499
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Page last updated May 8, 2017

PGC 18516 (= "IRAS 06076-2139")
A magnitude 14.5(?) pair of galaxies in
Northern galaxy position RA 06 09 45.8, Dec -21 40 23
Southern galaxy position RA 06 09 46.0, Dec -21 40 31
Historical Discussion: Catalogued in the PGC in 1989, independently named by the IRAS (InfraRed Astronomical Satellite) survey in the 1980's. The paper noted below, which will soon result in a far more detailed discussion of the pair, was published in 2008, and the HST image that brought the object to my attention was posted May 8, 2017.
Summary: A pair of galaxies separated by about 20 thousand light years, with relative motions of about 2 million km/hr (550 km/sec). Given their relative speed, they will pass each other without any chance of merger, but their near encounter is already affecting their structures, with one showing a ring of hot young stars around a central starburst, and the other a nucleus filled with stellar birthplaces, and stars and gas flung outward in all directions.
Effects of the Near-Collision: The HST release points out that stars are so small that they are "not affected" by the passage of the galaxies by/through each other; but although they may not suffer collisions with other stars, their galactic orbits are drastically changed by the gravitational interaction of the galaxies, hence the scattering of gas and stars throughout vast regions surrounding the galaxies, and the exchange of some stars from one galaxy to another. What happens to planets and other objects orbiting the stars can't be as certainly known. Close planets, such as those in the inner Solar System, probably continue to orbit their stars without any significant effects; but more distant ones, such as Uranus, Neptune and Pluto, might be torn away from their stars if there was an unusually close passage by another star, and very distant objects such as comets in the Oort Cloud, would almost certainly have their orbits disrupted.
Physical Information: Vr 11225 km/sec, z 0.037446. Overall apparent size about 0.45 by 0.3 arcmin? Per the paper noted below, apparent separation of the two nuclei is about 8 arcsec (from the images below), and recessional velocities differ by about 550 km/sec (from the paper noted above). More details to be published as soon as I've read all of the paper that showed this was a double system.
DSS image of region near galaxy pair PGC 18516
Above, a 12 arcmin wide DSS image centered on PGC 18516
Below, a 0.6 arcmin wide PanSTARRS image of the pair of galaxies
PanSTARRS image of galaxy pair PGC 18516
Below, a 0.8 arcmin wide HST image of the pair (Image Credit ESA/Hubble & NASA)
HST image of galaxy pair PGC 18516
Below, a 0.4 by 0.6 HST image of the pair (Image Credit as above)
HST image of galaxy pair PGC 18516

PGC 18948
A 13th-magnitude lenticular galaxy (type (R1)SB(r)0/a) in
Canis Major (RA 06 23 46.4, Dec -32 13 00)
Based on a recessional velocity of 6725 km/sec, PGC 18948 is about 310 million light years away. Given that and its apparent size of 1.5 by 1.4 arcmin, it is about 135 thousand light years across. Used by the de Vaucouleurs Atlas of Galaxy Types (as ESO 426-2) as an example of type (R1)SB(r)0/a. (Note: the image in the de Vaucouleurs Atlas does not have North at the top.)
DSS image of region near lenticular galaxy PGC 18948
Above, a 12 arcmin wide DSS image centered on PGC 18948
Below, a 2.4 arcmin wide DSS image of the galaxy
DSS image of lenticular galaxy PGC 18948
Celestial Atlas
PGC 18000 - 18499 ←     PGC Objects: PGC 18500 - 18999     → PGC 19000 - 19499