A face-on spiral galaxy in shades of muted yellow and cream has a bright central core, surrounded by an oval-shaped bright ring. The core is offset from the center of the ring to the bottom left. It looks a little like a fried egg. Outside of the ring are wispy spiral arms that are not well defined. The arms spiral clockwise from the edge of the ring. The background is dotted with yellow and orange stars and tiny background galaxies.

Legacy Surveys image of Arp 10, also known as UGC 1775.

A galaxy likely collided with Arp 10 near its center. A density wave rippled outwards, creating a ring of new stars in the freshly compacted gas.

Credit: Legacy Surveys, D. Lang, NERSC, Meli thev, Wikimedia Commons
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A slightly inclined spiral galaxy. In the center is a bright yellow core. The galaxy's stars and gas form a loose two-armed barred spiral, forming an S-shape. Dark, filamentary dust lanes and pink regions of star formation are seen throughout the spiral arms. At the bottom edge of the galaxy, in line with the bar, is what looks like a third spiral arm.

Kitt Peak National Observatory image of Arp 18, also known as NGC 4088.

NGC 4088 is an asymmetric spiral galaxy, located about 40 million light years away.

Credit: KPNO, NOIRLab, NSF, AURA, Bonnie Fisher, Mike Shade, Adam Block
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A face-on barred spiral galaxy anchored by its central region. It has a bright white circular area surrounded by a lighter pinkish diagonal bar structure made of a haze of stars, which forms an angled oval toward the top. Two distinct spiral arms made of stars, gas, and reddish brown filamentary dust lanes start at the center and extend outward, rotating clockwise. The outer spiral arms are made of many yellow clusters of stars. The background of space beyond the galaxy appears black. There are some large blue and red points of light surrounding the galaxy. A white box outlines the center part of the galaxy. An insert shows the X-ray only light from the area covered by the box. In the insert are blue points of light and a blue haze on a black background. The blue haze roughly corresponds to the location of the galaxy’s bar in images taken at other wavelengths. A series of bright blue points are at the center of the hazy structure.

Composite image of Arp 16, also known as M66.

Chandra (X-ray, blue), Spitzer (infrared, red), Hubble and VLT (visible light, yellow). Insert shows hot gas near the supermassive black hole.

Credit: NASA, STScI, JPL-Caltech, ESO, WFI, CXC, Ohio State Univ., C.Grier et al
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An abstract, blobby, purple area of hot X-ray gas. In the center is a somewhat extended bright point. Areas of fainter gas extend roughly horizontally to the left and right. Below the extended central point is a smaller bright point, likely a smaller black hole or neutron star in the galaxy, or a background supermassive black hole.

Chandra image of Arp 220, also known as IC 4553.

This X-ray image shows the hottest gas in two merging spiral galaxies. The central bright point contains their remnant cores, which are about 1,200 light-years apart.

Credit: NASA, CXC, SAO, L. Frattare, J. Major
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The yellow core of a disrupted spiral galaxy is surrounded by irregular, translucent spiral arms. The inner part of the galaxy is seen at an angle, so that it appears oval-shaped rather than circular. Dark brown dust lanes and pink star forming regions cross a yellow haze of older stars. The faint blue arms unfurl from the center, like paint flung out of a spinning canvas. They are dotted with blue star clusters. The arms stretch out to the right of the frame. The black background of space is filled with foreground stars and tiny background galaxies.

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
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A pair of interacting galaxies. The galaxy on the left is likely an edge-on disk galaxy, appearing as a slightly warped, fuzzy, white horizontal line with dust filaments at its center. It is surrounded by a red glow on the left part of the galaxy and a green glow at its right edge. The galaxy on the right is a ring galaxy, appearing as a blue circular ring, dotted with blue star clusters, that also has its center partially filled in with blue star clusters. The two galaxies overlap so that the right end of the edge-on galaxy intersects with the ring galaxy's center. It looks a bit like a big blue hand holding the Enterprise in a classic episode of Star Trek.

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
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A face-on barred spiral galaxy anchored by its central region. It has a bright yellow circular area surrounded by a lighter yellow diagonal bar structure made of a haze of stars, which forms an angled oval toward the top. The central core and bar fill about a third of the image. Two distinct spiral arms made of stars, gas, and brown filamentary dust lanes start at the center and extend to the edges, rotating clockwise. The farther the arms are from the central region the easier it is to see bright blue clusters of stars, which appear as pinpricks. The darkest areas of the arms are two large dusty arcs that start at the central region. One to lower left extends toward the top and the second starts at the top-right and extends to the bottom. The background of space beyond the galaxy appears dark gray. There are some fine red points of light toward the bottom half and top right. A triangular area at center-right is black, reflecting where there isn't any data.

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
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A greyscale image of three disk galaxies arranged in a triangle. To the left is the largest galaxy, likely a lenticular galaxy, which has a bright center and a series of shells, which appear as arc-like glowing features with sharp outer edges. A few dark dust lanes appear in this outer part of the disk. The large galaxy overlaps with the galaxy to the right, which is also probably a lenticular galaxy. It has a bright center surrounded by a hazy disk. A faint curving feature, either a spiral arm or a tidal tail, emerges at about 6 o'clock and curves counterclockwise around the galaxy. The third galaxy, the smallest of the three, is below the other two. It's center is just below the center of the left galaxy. It has a bright center, a central bar structure, and two clearly defined spiral arms. A bright foreground star is above the right galaxy, and has large diffraction spikes which overlap with the galaxies. The image has a noticeable amount of detector noise which has not been removed. The black background of space is dotted with stars and small background galaxies.

Hubble image of Arp 221.

Arp 221 is an interacting trio of disk galaxies. To the right is what is probably a large lenticular galaxy, with a series of shells that are caused by the gravitational interactions or a past merger.

Credit: NASA, ESA, STScI, J. Dalcanton, Judy Schmidt
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A grainy, black and white image of a nearly face-on barred spiral galaxy. It has a bright core. Two spiral arms start at the center and extend outward, rotating clockwise. They are crossed by dark dust lanes. Several white dots, which are stars, are seen on the black background.

Image of Arp 16, also known as M66, from Halton Arp's Atlas of Peculiar Galaxies (1966).

In the original catalog it was in the category: Spiral galaxies - Detached segments. M66 has loose arms full of young star clusters.
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A greyscale image of a galaxy with a line-like nucleus and a horseshoe-shaped arc above it. The horseshoe points down, and the nucleus is in the center of the arc. It looks like an upside down power symbol, ⏻. The nucleus and horseshoe are dotted with bright star clusters and dark dust lanes.

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
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A grainy, black and white image of a distorted spiral galaxy. It is seen at a skewed angle, so it appears as an oval rather than a circle. A thick, stormy disc of material surrounds a bright center, with swirling strands of dark dust and bright star clusters strewn through the disk. A large spiral arm extends from about 12 o'clock to about 6 o'clock. Some foreground stars are visible atop the galaxy. Many white dots, which are stars, are seen on the black background.

Image of Arp 184, also known as NGC 1961, from Halton Arp's Atlas of Peculiar Galaxies (1966).

In the original catalog it was in the category: Amorphous galaxies - Narrow filament. NGC 1961 is an extremely massive spiral galaxy with irregular arms.
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A face-on spiral galaxy. In the center is a small yellow bar structure. A single large blue spiral arm begins at the top and curves counter-clockwise from about the 12 o'clock to 11 o'clock positions. This gives the galaxy a teardrop-shape with a curved end, so that it resembles a paisley. Brown dust lanes, blue star clusters, and pink star forming regions are scattered throughout the galaxy.

NTT image of Arp 22, also known as NGC 4027.

NGC 4027 is a barred spiral galaxy with a single spiral arm. It is interacting with a smaller companion galaxy, NGC 4027A, which is just out of frame.

Credit: ESO
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A grainy, black and white image of a galaxy. The galaxy's stars and gas form a patchy, loose, two-armed spiral with a central bar. A few white dots, which are stars, are seen on the black background.

Image of Arp 2, also known as UGC 10310, from Halton Arp's Atlas of Peculiar Galaxies (1966).

In the original catalog it was in the category: Spiral galaxies - Low surface brightness. It is a barred Magellanic spiral galaxy.
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A somewhat low-res image of a one-armed barred spiral galaxy. The bar, seen as a bright white line of stars and star clusters anchors the galaxy. Beginning at about the 3 o'clock position, a spiral arm wraps clockwise around the galaxy, ending at around 12 o'clock. The arm is formed from a haze of yellow-green stars and are dotted with bright blue-green star clusters. To its upper right is a smaller galaxy. It has a bright yellow center and a more diffuse disk or halo of stars. Dotted across the black background of space are small background galaxies and foreground stars.

Sloan Digital Sky Survey image of Arp 291, also known as UGC 5832.

This one-armed barred spiral galaxy may be interacting with the small galaxy above it and to the right.

Credit: SDSS
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On a black, starry background are three bright objects in a horizontal row at the center. On the left is a bright star with four diffraction spikes. To its lower right is a large spiral galaxy filled with streaks of blue and pink. Its right-side arm appears to be breaking away from the rest of the galaxy, being pulled toward the third object on the far right, another galaxy. This galaxy is yellow and smoothly increases in brightness toward its center.

Ground-based image of Arp 25, also known as NGC 2276.

NGC 2276 (left) is being pulled by the neighboring galaxy NGC 2300 (right). NGC 2276 is rich in new star formation along its spiral arms.

Credit: NASA, ESA, STScI, Adam Block (Steward Observatory)
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Two small galaxies appear on a sparse field of stars. At center left is NGC 2523, a face-on barred spiral. It has a bright yellow central core with a horizontal bar-shaped structure that connects to a thin ring. The area between the ring, core, and bar is dark. This central part looks like a steering wheel. The spiral arms originate at the ring and spiral outward counterclockwise. The arms are dotted by blue star clusters and shrouded in a haze of stars. At right center is NGC 2523B, an edge-on spiral. It has a yellow central bulge and a blue disk, which is crossed by a central brown dust lane.

Kitt Peak National Observatory image of Arp 9, also known as NGC 2523.

NGC 2523 is the bright barred spiral galaxy on the left side of the frame. The edge-on spiral galaxy to the right, NGC 2523 B, is in the same galaxy group.

Credit: KPNO, NOIRLab, NSF, AURA, Adam Block
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Two merging galaxies form an orange and blue abstract butterfly shape. Within the shape are bright blue areas, which are clusters of young, hot stars. These are found in the center, the upper right "wing", and the bottom left "wing".

Hubble image of Arp 299, also known as NGC 3690.

This image was taken in 2000 with Hubble WFPC2 instrument to study the merging galaxies' hottest and brightest stars in ultraviolet light.

Credit: NASA, R. Windhorst, and the Hubble mid-UV team
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Two ring-like galaxies. On the left is a galaxy with a bright core surrounded by a yellow ring. There is a gap between the core and ring where the black background of space shows through. The galaxy is tilted so that the circular ring appears oval-shaped. On the right is a another circular galaxy, made mostly of a ring of bright blue dots, which are star clusters. A series of large pink blobs dot the ring from about 6 o'clock to 1 o'clock. On the bottom left part of the ring is a haze of white stars and orangish dust. The center of the ring is empty and the black background of space shows through. This galaxy looks a little like the writing of the aliens from the movie Arrival.

Hubble and Chandra image of Arp 147, also known as IC 298.

The pink dots are Chandra data. The points in the ring are so bright that they must be black holes with masses about 10 times the Sun, pulling matter from companions.

Credit: NASA, STScI, CXC, MIT, S.Rappaport et al.
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Two interacting galaxies appear on a field of stars. A black and white image of the galaxies taken in visible light is overlaid with radio (blue) and infrared (pink) images. The bottom galaxy is a large spiral. It is tilted slightly, so that its disk forms an oval rather than a circle. The top galaxy is a bright elliptical galaxy. It is oval shaped with a bright center that gets gradually fainter and more transparent towards its edges. A plume of gas and stars surrounds and appears to rise from the galaxies, like smoke from a campfire. The blue radio light snakes around the outside of the spiral galaxy, through the elliptical galaxy and into the plume, forming a teardrop shape. The pink infrared light highlights the centers of the spiral and elliptical galaxies.

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
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A large spiral galaxy is seen in the center of the frame. It's tilted at an angle, so that it's disk appears as an oval rather than a circle. Dramatic dust lanes cross in front of the center of the galaxy and are backlit by a haze of yellow-white stars. Above the spiral is a smaller disk galaxy seen in shades of blue white. It appears to be at almost a right angle to the large spiral, falling into the larger galaxy. The two galaxies are connected by a bridge of dusty tendrils, which are also backlit by the main galaxy. This galaxy pair looks a lot more 3D than most interacting galaxies because of their angles and the backlighting effect.

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
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A pair of interacting spiral galaxies. In the center of the frame is the larger galaxy, a spiral galaxy seen face-on. It has a bright center. A ring of pale pink stars and star clusters circles the center, giving the inner part of the galaxy a shape that resembles an eye. Two long spiral arms emerge from the ring, dotted with pale blue star clusters. The upper arm trails off in a faint arc to the right. The bottom arm appears to connect to its companion galaxy in the lower part of the frame. This galaxy is smaller and less well defined, but is still clearly a two-armed spiral with a bright center and wider, hazy arms. The black background of space is dotted with foreground stars and tiny background galaxies. A few particularly bright stars with diffraction spikes are seen to the right of the center galaxy.

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
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A distorted galaxy with looping tidal tails. In the center of the frame is a galaxy with a bright yellow center. A dark brown dust lane divides the bright center of the galaxy in two. It's hard to tell if this dust is blocking a continuous bright area or if there are two distinct nuclei. The disk of the galaxy surrounds the center, probably seen nearly edge-on, made of a haze of older yellow stars. At the left and right edges of the disk are blue clusters of younger stars. One stream of gas and stars, a tidal tail, starts at the left edge of the disk, loops under the galaxy, and connects with the bottom right edge of the disk. A second stream of gas begins at the top right edge of the disk, loops over the galaxy, and then connects to the top left edge of the disk. Together, these two tidal tails form a rough ring shape. Another fainter tidal tail starts at the apex of the top arc and continues diagonally up and to the left. A smaller galaxy, an almost edge-on spiral, is below and to the left of the central galaxy.

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
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A lower-res black and white image of three widely separated galaxies on the black background of space. The bright parts of the galaxy are overexposed, so you do not see very many interior details of the galaxies. The galaxy at the upper left is an edge-on spiral, seen as a wide, bright line with a dark dust lane going through the middle. The galaxy at lower left is a spiral galaxy, seen as a bright oval. The galaxy at lower right is a nearly face-on spiral, seen as a bright oval.

Image of Arp 317, also known as the Leo Triplet, from Halton Arp's Atlas of Peculiar Galaxies (1966).

In the original catalog it was in the category: Double and multiple galaxies - Groups. NGC 3628 (bottom), M66 (upper right), M65 (upper left.)
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A greyscale image of a one-armed barred spiral galaxy fills most of the frame. The bar, seen as a bright line of stars and star clusters anchors the galaxy. Beginning at about the 3 o'clock position, a spiral arm wraps clockwise around the galaxy, ending at around 12 o'clock. The arm is formed from a haze of stars and are dotted with bright star clusters. In the upper part of the frame, partially cut off at the right edge, is a smaller galaxy. It has a bright center and a more diffuse disk or halo of stars. Dotted across the black background of space are small background galaxies and foreground stars. The image has a noticeable amount of detector noise which has not been removed.

Hubble image of Arp 291, also known as UGC 5832.

This one-armed barred spiral galaxy may be interacting with the small galaxy in the upper right corner of the frame.

Credit: NASA, ESA, STScI, Julianne Dalcanton, Meli thev, Wikimedia Commons
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A galaxy merger remnant has a face-on pinwheel-shaped disk in its center. The pinwheel has a white inner core that transitions to a blue area covered in spiraling brown dust lanes. The brown dust lanes continue outward partially into a hazy white area. This large, roughly circular area has a series of concentric shells outside of the pinwheel. The shells which appear as arc-like glowing features with sharp outer edges. Within the shells are a series of faint lines that jut out radially, they are tidal tails that extend beyond the frame of the image. The black background of space is dotted with stars and small background galaxies, including a few small, adorable spirals.

Hubble image of Arp 226, also known as NGC 7252 or the Atoms for Peace Galaxy.

It's peaceful nickname is somewhat ironic — its tidal tails, shells, and ripples reveal a violent merger between two gas-rich spiral galaxies in its past.

Credit: NASA ESA, J. Schmidt
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A grainy, black and white image of a galaxy. In the upper left corner is a spiral galaxy with a bright central core encircled by two wispy arms that form a loose spiral. The view is somewhat oblique, giving the galaxy an oval appearance. A long, thin, diffuse stream extends from the lower right side of the galaxy down to the lower right corner of the image. In the background there are a few circular dots, which are stars, and smudgy objects, which may be background galaxies.

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.
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A grainy, black and white image of two galaxies. The lower galaxy is large and faint. It has a central bar and a loose, patchy ring of star clusters. The top galaxy is smaller and brighter. It has two spiral arms, which spiral clockwise from a bright central point. The galaxy looks overexposed, so it is hard to see many details. Many white dots, which are stars, are seen on the black background.

Image of Arp 4, from Halton Arp's Atlas of Peculiar Galaxies (1966).

In the original catalog it was in the category: Spiral galaxies - Low surface brightness. The larger irregular galaxy is Arp 4, and the smaller spiral galaxy is PGC 6629.
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A grainy, black and white image of a group of interacting galaxies which resembles a question mark. At the top of the frame, a somewhat messy spiral shape formed by a pair of merging galaxies forms the top part of the question mark. At the bottom of the frame is another galaxy, which forms the dot of the question mark. A string of star clusters, seen as large dots, connects the galaxies, forming the straight part of the question mark. A few white dots, which are stars, are seen on the black background.

Image of Arp 194, also known as UGC 6945, from Halton Arp's Atlas of Peculiar Galaxies (1966).

In the original catalog it was in the category: Amorphous galaxies - Material ejected from nuclei. This interacting group has several spiral galaxies.
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A pair of spiral galaxies. The upper galaxy is seen face-on. It has a bright center and short bar structure that transitions into a series of loosely-wound spiral arms, looking something like a cinnamon roll. The arms are dotted with blue star clusters and crossed by darker dust filaments. The lower galaxy is seen edge on. It has a somewhat puffy disk, seen as a wide, almost vertical, yellow line. Running down the middle is a dark dust lane with a few blue star clusters peaking out. In the middle of the frame, where the two galaxies appear to touch, is a bright foreground star with four diffraction spikes. Other distant galaxies and stars fill the black background of space.

Hubble image of Arp 302, also known as UGC 9618 or VV 340.

This image of a pair of very gas-rich spiral galaxies is one of 59 images of merging galaxies taken by the Hubble Space Telescope and released for its 18th anniversary in April 2008.

Credit: NASA, ESA, STScI, A. Evans
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A black, deep-space background is punctuated with more than a hundred randomly spaced red, white and orange galaxies in this astronomical image. These galaxies are various shapes and apparent sizes. Dominating the foreground is an object that at first appears to be a brilliant, 6-pointed, orange star surrounded by wisps of orange gas and bluish purple nebulosity. In reality, what seems to be a star is actually two colliding galaxies with merging cores. The brilliant light from the star-formation surrounding these cores creates diffraction spikes — the prominent starburst feature. Several tiny, whitish yellow regions appear almost dead center on this feature. On the outskirts of the merger are faint, grainy, nearly transparent areas that look like bluish purple clouds. Reddish orange streams and filaments appear across the foreground object.

JWST image of Arp 220, also known as IC 4553.

Arp 220 is two spiral galaxies in the process of merging. The merger sparked a burst of star formation in their cores. Those small, bright areas created the six large diffraction spikes.

Credit: NASA, ESA, CSA, STScI, A. Pagan
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