Hubble image of Arp 299, also known as NGC 3690. Interactions between these two galaxies triggered a fierce burst of star formation, making Arp 299 one of the most powerful nearby starburst galaxies. Credit: NASA, ESA, the Hubble Heritage Team, A. Evans Source

Image of Arp 7, from Halton Arp's Atlas of Peculiar Galaxies (1966). In the original catalog it was in the category: Spiral galaxies - Split arms. It is a barred spiral galaxy in the constellation Hydra. Source

Kitt Peak National Observatory image of Arp 104, also known as NGC 5216 and NGC 5218, or Keenan’s System. A bridge of stars and gas about 7,000 light years wide and 150,000 light years long connects the two galaxies. Credit: NOIRLab, NSF, AURA, T.A. Rector, H. Schweiker Source

Hubble image of Arp 219, also known as UGC 2812. Interactions with a companion likely formed these loops of material. In this image, the luminosity comes from Hubble observations, and color from PanSTARRS. Credit: NASA, ESA, STScI, J. Dalcanton, Judy Schmidt, PanSTARRS Source

NuStar image of Arp 299, also known as NGC 3690. X-ray light from NuSTAR highlights an active supermassive black hole in one of the galaxies in the pair Arp 299. The other galaxy lacks an active black hole and is not seen in the image. Credit: NASA, JPL-Caltech, GSFC Source

Image of Arp 282, also known as NGC 169 and NGC 169A, from Halton Arp's Atlas of Peculiar Galaxies (1966). In the original catalog it was in the category: Double and multiple galaxies - Infall and attraction. Tidal streams visibly link the pair. Source

Image of Arp 188, also known as Tadpole Galaxy, from Halton Arp's Atlas of Peculiar Galaxies (1966). In the original catalog it was in the category: Amorphous galaxies - Narrow filament. The tail is a result of a recent galactic interaction. Source

Hubble image of Arp 190, also known as UGC 2320. Interactions between an elliptical galaxy off frame to the left and the lower spiral galaxy created the large tidal tail that extends to the right. Credit: ESA, NASA, J. Dalcanton, J. Schmidt Source

Image of Arp 298, also known as NGC 7469 and IC 5283, from Halton Arp's Atlas of Peculiar Galaxies (1966). In the original catalog it was in the category: Double and multiple galaxies - Unclassified objects. The galaxies are an interacting pair. Source

Hubble image of Arp 87, also known as NGC 3808 and NGC 3808A. NGC 3808 (right) is a nearly face-on spiral galaxy interacting with NGC 3808A (left), a polar ring galaxy with an edge-on disk circled by a ring of stars and gas. Credit: NASA, ESA, and the Hubble Heritage Team Source

Spitzer, VLA, and CFHT MegaCam image of Arp 94, also known as NGC 3226 and NGC 3227. The grayscale image shows visible starlight. Cool hydrogen gas (blue), floods the top galaxy and shuts down star formation. Credit: NASA, CFHT, NRAO, JPL-Caltech, Duc, Cuillandre Source

GALEX and SDSS image of Arp 283, also known as NGC 2798 and NGC 2799. The left galaxy in this interacting pair, NGC 2799, is viewed edge-on. A bridge with clumps of star formation appears to connect it to NGC 2798, at right. Credit: Fig. 12 from Smith et al. 2010. Source

Image of Arp 148, also known as Mayall's Object, from Halton Arp's Atlas of Peculiar Galaxies (1966). In the original catalog it was in the category: Amorphous galaxies - Associated rings. The two galaxies colliding likely created the ring. Source

Hubble image of Arp 70, also known as VV 341. In Arp 70, a larger galaxy with two well-defined spiral arms interacts with a small companion. Such interactions have been linked to the production of grand-design spiral arms. Credit: NASA, ESA, STScI, J. Dalcanton, Judy Schmidt Source

Very Large Telescope image of Arp 271, also known as NGC 5426 and NGC 5427. The galaxies are tugging on each other with gravity, which has begun to distort their features and may have also triggered bursts of star formation. Credit: ESO Source

Image of Arp 289, also known as NGC 3981, from Halton Arp's Atlas of Peculiar Galaxies (1966). In the original catalog it was in the category: Double and multiple galaxies - Wind effects. Interactions with another galaxy likely caused its odd arms. Source

Hubble image of Arp 55, also known as UGC 4881. This pair of galaxies is about halfway through a merger. Their cores are separate, but their disks are overlapping. Credit: NASA, ESA, STScI Source

Hubble Space Telescope image of Arp 6, also known as NGC 2537 or the Bear’s Paw Galaxy. It has a nucleus that is rapidly forming stars, surrounded by a horseshoe-shaped structure, also forming new stars. Credit: NASA, ESA, STScI, J. Dalcanton, Judy Schmidt Source

Image of Arp 271, also known as NGC 5426 and NGC 5427, from Halton Arp's Atlas of Peculiar Galaxies (1966). In the original catalog it was in the category: Double and multiple galaxies - Connected arms. The two galaxies are interacting. Source

Hubble and Spitzer image of Arp 148, also known as Mayall's Object. Dusty material in the edge-on galaxy (left) glows brightly in the infrared light seen by Spitzer (red). Starlight dominates the visible light from Hubble (blue and green). Credit: NASA, JPL-Caltech, STScI Source

ARP! ARP! ARP! ☄️🔭 arxiv.org/abs/2509.09011

Hubble and Pan-STARRS image of Arp 6, also known as NGC 2537 or the Bear’s Paw Galaxy. The horseshoe structure may be the result of a shockwave from a nuclear starburst. Credit: NASA, ESA, STScI, J. Dalcanton, Judy Schmidt, PanSTARRS Source

Image of Arp 6, also known as NGC 2537 or the Bear’s Paw Galaxy, from Halton Arp's Atlas of Peculiar Galaxies (1966). In the original catalog it was in the category: Spiral galaxies - Low surface brightness. Source

Image of Arp 202, also known as NGC 2719 and NGC 2719A, from Halton Arp's Atlas of Peculiar Galaxies (1966). In the original catalog it was in the category: Amorphous galaxies - Material ejected from nuclei. Arp 202 is an interacting galaxy pair. Source

Spitzer image of Arp 16, also known as M66. The blue core and bar has a concentration of blue older stars, and the pink bar ends and spiral arms show dust heated by actively forming stars. Credit: NASA/JPL-Caltech/R. Kennicutt (University of Arizona) and the SINGS Team Source

Hubble image of Arp 298, also known as NGC 7469 and IC 5283. NGC 7469, a face-on spiral galaxy, and its companion galaxy IC 5283, seen to the upper right, form an interacting pair. Credit: ESA, NASA, A. Evans, R. Chandar Source

Hubble Space Telescope image of Arp 4. This image contains two galaxies, a larger irregular galaxy, Arp 4, and a small spiral galaxy PGC 6629. Credit: NASA, ESA, STScI, J. Dalcanton, Judy Schmidt, Pan-STARRS Source

Composite image of Arp 298, also known as NGC 7469 and IC 5283. X-rays from Chandra (purple) are overlaid on a Hubble and JWST image of NGC 7469. Credit: NASA, CXC, X. Xu; NASA, ESA, UVA, NRAO, A. S. Evans, Hubble Heritage team; NASA, ESA, CSA, L. Armus, A. S. Evans; J. Major Source

Kitt Peak image of Arp 297, also known as NGC 5755, NGC 5753, NGC 5754 and NGC 5752. This wide view shows two interacting galaxy pairs. The pairs are actually unrelated and are at different distances. Credit: KPNO, NOIRLab, NSF, AURA, B. Lofquist, A. Block Source

Pan-STARRS image of Arp 7. It is a barred spiral galaxy in the constellation Hydra. Credit: Pan-STARRS1 Surveys (PS1) Source

Hubble and Dark Energy Camera image of Arp 122, also known as NGC 6040 and LEDA 59642. This pair of galaxies are in the midst of a collision, warping the top spiral NGC 6040. Credit: ESA, NASA, J. Dalcanton, Dark Energy Survey, DOE, FNAL, DECam, CTIO, NOIRLab, NSF, AURA Source

ALMA image of Arp 16, also known as M66. This image of M66 shows the location of cold clouds of molecular gas. It’s in these cold, dusty clouds that new stars form. Credit: ESO, ALMA (ESO/NAOJ/NRAO), PHANGS Source

Hubble image of Arp 82, also known as NGC 2535 and NGC 2536. The larger galaxy's arms have evenly spaced "beads on a string" star clusters, created by recent gravitational interactions that led to a burst of star formation. Credit: NASA, ESA, STScI, J. Dalcanton, Judy Schmidt Source

Image of Arp 8, also known as NGC 497, from Halton Arp's Atlas of Peculiar Galaxies (1966). In the original catalog it was in the category: Spiral galaxies - Split arms. It is a barred spiral galaxy in the constellation Cetus. Source

Hubble image of Arp 256. A recent close interaction between these two galaxies distored the shapes of thier disks and triggered a burst of star formation, seen in the blue clusters of hot, young stars. Credit: ESA, NASA Source

Hubble Space Telescope image of Arp 5, also known as NGC 3664. NGC 3664 is a barred Magellanic spiral galaxy with a single spiral arm and prominent bar. It is interacting with a dwarf galaxy, out of frame. Credit: NASA, ESA, STScI, Solomon Hendrix Source

CFHT SITELLE image of Arp 82, also known as NGC 2535 and NGC 2536. Simulations suggest the two galaxies are in the early stages of a merger. The pair already experienced one collision and are just about to collide again. Credit: Fig. 1 from Prime et al. 2022 Source

VLT image of Arp 289, also known as NGC 3981. This image was captured as part of the ESO Cosmic Gems Program, which uses the Very Large Telescope to photograph beautiful objects in the southern skies when conditions don’t allow scientific observations to be made. Credit: ESO Source

Image of Arp 94, also known as NGC 3226 and NGC 3227, from Halton Arp's Atlas of Peculiar Galaxies (1966). In the original catalog it was in the category: Spiral galaxies - Elliptical companions. Spiral NGC 3227 interacts with elliptical NGC 3226. Source

Hubble image of Arp 288, also known as NGC 5221. In 2016, a supernova appeared in the galaxy's long tidal tail to the right, about 260 thousand light years from the galactic center. Credit: NASA, ESA, STScI, J. Dalcanton, Judy Schmidt Source

Image of Arp 23, also known as NGC 4618, from Halton Arp's Atlas of Peculiar Galaxies (1966). In the original catalog it was in the category: Spiral galaxies - One-armed. Its unusual shape may come from interactions with its companion. Source

Composite image of Arp 26, also known as M101 or the Pinwheel Galaxy. It combines data from X-ray (Chandra, purple), infrared (Spitzer, red), visible light (Hubble, yellow), and ultraviolet (GALEX, blue) telescopes. Credit: NASA, CXC, SAO;NASA, JPL-Caltech;NASA, STScI Source

Hubble image of Arp 116, also known as M60 and NGC 4647. M60 is a giant elliptical galaxy. The smaller spiral NGC 4647 is about the size of our galaxy, the Milky Way. While it is not obvious, the two galaxies are just beginning to interact. Credit: NASA, ESA, STScI Source

Hubble image of Arp 282, also known as NGC 169 and NGC 169A. Interactions between the two galaxies create delicate streams that visibly link the pair. Credit: ESA/Hubble & NASA, J. Dalcanton, Dark Energy Survey, DOE, FNAL/DECam, CTIO/NOIRLab/NSF/AURA, SDSS, J. Schmidt Source

Image of Arp 200, also known as NGC 1134, from Halton Arp's Atlas of Peculiar Galaxies (1966). In the original catalog it was in the category: Amorphous galaxies - Material ejected from nuclei. It is likely interacting with a small companion. Source

Spitzer image of Arp 107, also known as UGC 5984. The short wavelength left image highlights older stars, while the longer wavelength middle image highlights younger stars. The multi-band picture shows the two stellar age groups. Credit: NASA, JPL-Caltech, B. J. Smith Source

Hubble Space Telescope image of Arp 16, also known as M66. M66 was discovered by Charles Messier on 1 March 1780, object 66 in his catalog of “fuzzy things in the night sky that are not comets." He described it as "very long and very faint." Credit: NASA, ESA, STScI Source

Image of Arp 3, from Halton Arp's Atlas of Peculiar Galaxies (1966). In the original catalog it was in the category: Spiral galaxies - Low surface brightness. Source

Hubble image of Arp 220, also known as IC 4553. The image shows the center of the two merging spiral galaxies that make up Arp 220. The merger set of a burst of star formation, which backlights the large amount of dust in this visible light view. Credit: NASA, ESA, C. Wilson Source

Image of Arp 286, also known as NGC 5560, NGC 5566, and NGC 5569, from Halton Arp's Atlas of Peculiar Galaxies (1966). In the original catalog it was in the category: Double and multiple galaxies - Infall and attraction. Source