Free Astronomy Magazine

20 T his impressive image shows the strangely lopsided spiral gal- axy NGC 772, which lies over 100 million light-years from Earth in the constellation Aries. Captured by the Gemini North telescope in Hawai’i, one half of the interna- tional Gemini Observatory, a Pro- gram of NSF’s NOIRLab, the image shows NGC 772’s overdeveloped spi- ral arm, which stretches across to- ward the left-hand edge of the frame. This extra large arm is due to one of NGC 772’s unruly neighbors, the dwarf elliptical galaxy NGC 770. The tidal interactions between NGC 772 and its diminutive companion have distorted and stretched one of the spiral galaxy’s arms, giving it the lopsided appearance seen in this image. NGC 772 also lacks a bright central bar. Other spiral galaxies such as the Andromeda Galaxy or our own Milky Way exhibit promi- nent central bars — large, linear structures composed of gas, dust, and countless stars. Without a bar, NGC 772’s spiral arms sweep out di- rectly from the bright center of the galaxy. The galaxy’s unusual appear- ance has earned it the distinction of appearing in the Atlas of Peculiar Galaxies, a careful curation by as- tronomer Halton Arp of some of the weird and wonderful galaxies popu- lating the Universe. The 338 galaxies T he overdeveloped spiral arm of the galaxy NGC 772, which was created by tidal interactions with an unruly neighbor, dominates this ob- servation made by astronomers using the Gemini North telescope located near the summit of Mau- nakea in Hawai’i. [International Gemini Observatory/NOIRLab/NSF/ AURA. Image processing: T.A. Rec- tor (University of Alaska Anchor- age), J. Miller (Gemini Observa- tory/NSF’s NOIRLab), M. Zamani & D. de Martin] An extra large galactic arm by NOIRLab Amanda Kocz in the Atlas are a rogues’ gallery of strange and unusual galaxy shapes chosen to provide astronomers with a catalog of odd galaxy structures. Entries in the Atlas of Peculiar Galax- ies include galaxies boasting trailing tidal tails, rings, jets, detached seg- ments, and a host of other structural idiosyncrasies. NGC 772 is included as Arp 78. While NGC 772’s peculiarities dominate this image, there is also a menagerie of galaxies lurking in the background. The bright smears and smudges littering this image are dis- tant galaxies — some of the closer examples can be resolved into char- acteristic spiral shapes. Every direc- tion on the sky that astronomers have pointed telescopes toward con- tains a rich carpet of galaxies, with an estimated 2 trillion galaxies in total in our observable Universe. !