Galaxy NGC 772’s overgrown spiral arm, which was created by tidal interactions with an unruly neighbor, dominates this observation made by astronomers using the Gemini North Telescope near the summit of Maunakea in Hawai’i. Credit: Gemini International Observatory / NOIRLab / NSF / AURA; Image processing: TA Rector (University of Alaska Anchorage), J. Miller (Gemini Observatory/NSF’s NOIRLab), M. Zamani & D. de Martin
This impressive image shows the strangely unbalanced spiral galaxy NGC 772, which lies more than 100 million light-years from Earth in the constellation Aries. Captured by the Gemini North Telescope in Hawai’i, half of the Gemini International Observatory, a program of NSF’s NOIRLab, the image shows the overgrown spiral arm of NGC 772, which extends out to the left edge of the framework. This extra large arm is due to one of NGC 772’s unruly neighbors, the dwarf elliptical galaxy NGC 770. Tidal interactions between NGC 772 and its smaller companion have warped and stretched one of the spiral galaxy’s arms, making it giving the unbalanced appearance seen in this image.
NGC 772 also lacks a central light bar. Other spiral galaxies such as the Andromeda Galaxy or our own Milky Way feature prominent central bars – large linear structures made up of gas, dust and countless stars. Barless, the spiral arms of NGC 772 sweep straight out from the bright center of the galaxy.
The galaxy’s unusual appearance has earned it the distinction of appearing in the “Atlas of Peculiar Galaxies,” a careful selection by astronomer Halton Arp of some of the weird and wonderful galaxies that populate the universe. The 338 galaxies in the atlas are a rogue gallery of weird and unusual galaxy shapes chosen to provide astronomers with a catalog of weird galaxy structures. Entries in the “Atlas of Peculiar Galaxies” include galaxies with trailing tidal tails, rings, jets, detached segments, and a host of other structural idiosyncrasies. NGC 772 is included as Arp 78.
While the idiosyncrasies of NGC 772 dominate this picture, there’s also a menagerie of galaxies lurking in the background. The bright streaks and specks that litter this image are distant galaxies – some of the closest examples can be resolved into characteristic spiral shapes. Every direction in the sky that astronomers have pointed telescopes at contains a rich carpet of galaxies, with about 2 trillion galaxies in total in our observable universe.
Image: Hubble scans a particular pair of galaxies
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The spiral galaxy NGC 772 exhibits an overdeveloped spiral arm (2022, March 22)
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