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arpbot.bsky.social
Arp Bot 🤖
@arpbot.bsky.social
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Posting images of galaxies in Halton Arp's Atlas of Peculiar Galaxies (1966).

Automated account. Image curation, descriptions, typos, and most alt text by astronomer @kellylepo.bsky.social.

See posts for credits and links to the original sources.
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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
Source
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.
November 25, 2025 at 12:31 PM
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Image of Arp 300, also known as UGC 05028 and UGC 05029, from Halton Arp's Atlas of Peculiar Galaxies (1966).

In the original catalog it was in the category: Double and multiple galaxies - Unclassified objects.
Source
A grainy, black and white image of a pair of galaxies. The larger galaxy to the lower left is seen nearly face-on. It has a small core that transitions into clumpy spiral arms that are dotted with bright star clusters. More star clusters appear on the top of the galaxy, the side that faces its companion. The smaller galaxy to the upper right has a bright center that is surrounded by star clusters that only very roughly form spiral arms. Other distant galaxies and stars fill the black background of space.
November 25, 2025 at 12:31 AM
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Image of Arp 78, also known as NGC 772 and NGC 770, from Halton Arp's Atlas of Peculiar Galaxies (1966).

In the original catalog it was in the category: Spiral galaxies - Small, high surface brightness companions.
Source
A grainy, black and white image of a nearly face-on spiral galaxy. Appearing somewhat like an aerial view of a hurricane, the galaxy's spiral arms swirl around a bright center. The curling arms are defined by dark dust lanes. While the arms in the right half of the galaxy are somewhat poorly defined, in the left of the galaxy, one overdeveloped spiral arm curves clockwise from about 6 o'clock to about 11 o'clock. Since this arm flattens out near its end, in contrast to the rounder right half, the overall shape of the galaxy resembles a paisley. To its right, near the center, is its small companion galaxy, seen as a fuzzy oval. The black background of space is filled with many white dots which are stars.
November 24, 2025 at 12:31 PM
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Kitt Peak image of Arp 26, also known as M101 or the Pinwheel Galaxy.

This image was taken in 1975 image with the 4-meter Mayall telescope.

Credit: NOIRLab, NSF, AURA
Source
Black and white image of a face-on spiral galaxy. I has a bright core and several spiral arms, dotted with stars and star clusters, that spiral clockwise around the core. They are crossed by dark dust lanes. The arms are well-defined but asymmetric. One arm curls from about 6 o'clock to 9 o'clock and is mostly separated from the body of the galaxy. Another arm follows more closely to the core, from about 6 o'clock to 12 o'clock. Another other arms cover the area from 12 o'clock to 6 o'clock.
November 24, 2025 at 12:31 AM
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Hubble image of Arp 94, also known as NGC 3226 and NGC 3227.

The large spiral galaxy, NGC 3227 is interacting with its elliptical galaxy companion, NGC 3226. Faint tidal streams of gas and dust link the pair.

Credit: NASA, ESA, and H. Ford, G. Kober
Source
Two interacting galaxies. A large spiral galaxy with reddish brown dust lanes dotted with red star forming regions is in the left of the image. The galaxy's left half is cut off by the edge of the frame. The galaxy is tilted slightly, so that its disk forms an oval rather than a circle. A very faint bridge of material extends beyond the edge of the disk and appears to connect to its companion galaxy. In the center right is a bright elliptical galaxy. It is oval shaped with a bright center that gets gradually fainter and more transparent towards its edges. In the center of the galaxy are very faint brown dust lanes. The black background of space is dotted with foreground stars and tiny background galaxies.
November 23, 2025 at 12:31 PM
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Gran Telescopio Canarias image of Arp 271, also known as NGC 5426 and NGC 5427.

The mutual gravitational interaction of this pair of spiral galaxies distorts their shapes and creates a bridge of gas, dust and young stars that connect the galaxies.

Credit: GTC, IAC
Source
Two spiral galaxies take up most of the frame. At left is a more oblique galaxy that has a bright yellow core and fainter spiral arms dotted with pink star forming regions. At right is a nearly face-on spiral galaxy. It has a smaller yellow core and two well-defined spiral arms dotted with blue star clusters and pink star forming regions. The upper arm forks in two near its end. Near the center of the galaxy, the arms are crossed with brown dust lanes. The spiral arms of the two galaxies appear to form a faint bridge connecting the pair. The black background of space is dotted with stars and small background galaxies.
November 23, 2025 at 12:31 AM
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Dark Energy Camera image of Arp 289, also known as NGC 3981.

The galaxy's irregular arms is likely due to gravitational interactions with a neighboring galaxy.

Credit: Dark Energy Survey, DOE, FNAL, DECam, CTIO, NOIRLab, NSF, AURA, R. Colombari, M. Zamani
Source
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 cross a yellow haze of older stars. The blue arms unfurl from the center, like paint flung out of a spinning canvas. They are dotted with blue star clusters. The arms dip down more at the bottom of the frame. The black background of space is filled with foreground stars and tiny background galaxies.
November 22, 2025 at 12:31 PM
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Hubble and Legacy Survey 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: NASA, ESA, STScI, J. Dalcanton, Judy Schmidt, Legacy Surveys, D. Lang, NERSC
Source
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. Below 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 out of 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.
November 22, 2025 at 12:31 AM
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Sloan Digital Sky Survey image of Arp 8, also known as NGC 497.

NGC 497 is a barred spiral galaxy about 370 million light years away in the constellation Cetus.

Credit: SDSS
Source
A spiral galaxy with a small, bright, circular core. The muted, yellowish-green spiral arms wind clockwise around the yellow core. The galaxy is tilted slightly, so it forms an oval shape, rather than a circle. In the background are scattered red, yellow and green dots, which are stars.
November 21, 2025 at 12:31 PM
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Kitt Peak image of Arp 30, also known as NGC 6365.

Arp thought this was one galaxy with a particularly beefy arm. Later images show this is actually a pair of galaxies, one face-on and one nearly edge-on.

Credit: KPNO, NOIRLab, NSF, AURA, Friends' Central School, A. Block
Source
A tiny pair of spiral galaxies, one seen nearly edge-on and one seen face-on, appear on a larger field of stars. The face-on spiral at bottom has a bright orange central core and two well-defined spiral arms that loop counterclockwise around the galaxy. The inner parts of the spiral arms are yellow-white, while the outer arms fan out into blue stars and star clusters. One spiral arm begins at about 6 o'clock, curls around to the top of the galaxy at 12 o'clock and then ends at the bottom of the galaxy around 6 o'clock. The second arm begins at around 12 o'clock and curls around, ending at around 3 o'clock. The nearly edge-on galaxy overlaps at the top of the face-on galaxy, appearing like a continuation of the face-on galaxy's second spiral arm. It's disk is tilted, so it appears as a long, thin oval rather than a circle. The galaxy also has a yellow-white central core and an outer edge dotted with blue star clusters. In the black background of space are a few other colorful dots, which are foreground stars or background galaxies.
November 21, 2025 at 12:31 AM
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Image of Arp 70, also known as UGC 934, from Halton Arp's Atlas of Peculiar Galaxies (1966).

In the original catalog it was in the category: Spiral galaxies - Small, high surface brightness companions. The large galaxy interacts with its companion.
Source
A grainy, black and white image of a pair of interacting galaxies. The large barred spiral on the right takes up about half of the frame. It has a bright center that transitions into a nearly horizontal bar structure. Two spiral arms begin at the ends of the bar. Together the arms and the bar form an S-shape. A tear-dropped shaped loop surrounds the bar and connects the inner parts of the two spiral arms. The bottom spiral arm extends much farther than the upper spiral arm. Near the bottom of the frame the bottom arm curves back up and points to its companion galaxy. In the center left, above the larger galaxy, is a much smaller galaxy, seen as a featureless oval. The black background of space is filled with dots, which are foreground stars and background galaxies.
November 20, 2025 at 12:31 PM
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Image of Arp 107, also known as UGC 5984, from Halton Arp's Atlas of Peculiar Galaxies (1966).

In the original catalog it was in the category: Elliptical galaxies - Connected to spiral galaxies. Interactions led to the spiral's odd shape.
Source
A grainy, black-and-white image of a pair of merging galaxies. The galaxy on the left has a single, large spiral arm curving out from the core toward 3 o’clock and wrapping counterclockwise, ending in a straighter line pointing toward the bottom of the frame. The right-hand galaxy appears as an oval-shaped white blob. Small stars and galaxies are scattered throughout the black background of space, seen as circular white shapes.
November 20, 2025 at 12:31 AM
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Hubble Space Telescope image of Arp 15, also known as NGC 7393.

NGC 7393 is a barred spiral galaxy in the constellation Aquarius.

Credit: NASA, ESA, STScI, Julianne Dalcanton, Meli thev, Wikimedia Commons
Source
A greyscale image of a spiral galaxy. The faint galaxy has a central bar and two spiral arms that wind clockwise around the galaxy. The arms are crossed by dark dust lanes and dotted with bright star clusters. The image has some detector noise and lines from cosmic rays, which have not been removed.
November 19, 2025 at 12:31 PM
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VLT image of Arp 16, also known as M66.

This glittering image was taken with the MUSE instrument on ESO’s Very Large Telescope.
It highlights the galaxy's warm gas, hydrogen (red), oxygen (blue), and sulfur (orange).

Credit: ESO, PHANGS
Source
A face-on barred spiral galaxy. The image appears to be made out of a series of white and yellow dots, as well as a purple haze. The central region has a bright purple central dot surrounded by a lighter purple bar structure. Two distinct spiral arms start at the end of the bar, rotating clockwise. They appear to be a glittering gold color.
November 19, 2025 at 12:31 AM
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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
Source
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.
November 18, 2025 at 12:31 PM
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Hubble and NuStar image of Arp 299, also known as NGC 3690.

In the NuSTAR image (left panel), a supermassive black hole accretes gas and glows in X-rays. The black hole is in the right galaxy of a pair (see Hubble image, right panel).

Credit: NASA, JPL-Caltech, GSFC
Source
A three panel image. On the left is the NuStar image, in the center is the Hubble image, and in the middle is an image where the two are overlaid. In the left panel is a blurry, abstract image with blobs of white, pink, blue and yellow colors. The brightest area is a white blob to the lower right. In the center panel two merging galaxies form an abstract shape, which looks a little like an upside down rubber duck. Within the "head" and "body" of the duck are crossed brown swirls, which are dust and gas. The outside of the duck is outlined with hazy yellow swirls, which are streams of stars. Near the "neck" of the duck, at the point where the two merging galaxies touch, and slightly to the right is a bright white blob, surrounded by pink blobs. This is X-ray light from NuStar, which shows emission from an active supermassive black hole in the right galaxy. In the right panel is two merging galaxies form an abstract shape, which looks a little like an upside down rubber duck. WIthin the "head" and "body" of the dusk are blue-white dots, which are star clusters, and brown swirls, which are dust and gas. The outside of the duck is outlined with hazy yellow swirls, which are older stars.
November 18, 2025 at 12:31 AM
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Kitt Peak image of Arp 286, also known as NGC 5560, NGC 5566, and NGC 5569.

The galaxies in this triplett are gravitationally interacting. NGC 5566 is at center, NGC 5569 at bottom left, and NGC 5560 at top left.

Credit: NOIRLab, NSF, AURA, T.A. Rector, H. Schweiker
Source
The frame is dominated by three spiral galaxies. The largest is at the center of the frame. The disk of the galaxy is tilted, so that it appears oval-shaped, with the long axis running diagonally from upper right to lower left. It has a bright yellow-white center, surrounded by a ring structure. Emerging from the ring are two spiral arms, defined by faint dust lanes and blue star clusters. The arms trace the outline of the oval. A haze of yellow stars fills in the interior of the oval. At the bottom left is a smaller face-on spiral galaxy. Unlike the other two galaxies in the group, this galaxy does not appear distorted. It has a small bar structure in its center, surrounded by two loose spiral arms that are filled with blue star clusters. At upper left is a distorted spiral galaxy seen nearly edge-on. Its disk is warped, forming a thin, nearly vertical, backward S-shape. At the center of the disk is a faint bulge made out of a haze of stars.
November 17, 2025 at 12:31 PM
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Hubble image of Arp 194, also known as UGC 6945.

This interacting galaxy group includes a pair of merging galaxies with two nuclei and trails of blue super star clusters at top and a single large spiral galaxy at bottom.

Credit: NASA, ESA, and the Hubble Heritage Team
Source
A group of three interacting spiral galaxies which resembles a question mark. At the top of the frame are two spiral galaxies in the process of merging. One of these galaxies has a bright yellow core connected to a short bar and two loose spiral arms. This forms a S-shape. Above this is another circular, yellow galaxy core which overlaps with the top spiral arm of the S-shaped galaxy. On the outer edges of the spiral arms are blue star clusters. Together these form the top curved half of the question mark. To the right of the S-shaped galaxy is a small, relatively normal-looking spiral galaxy, which is likely in the background. At the bottom of the frame is another large spiral galaxy. This galaxy has a bright core and somewhat ill-defined spiral arms which wind counterclockwise around the core. On the bottom half of the galaxy are blue star clusters. This forms the dot of the question mark. Connecting the merging galaxies at the top of the frame and the spiral at the bottom of the frame is a string of blue super star clusters, seen as large blue dots. This forms the straight part of the question mark. On the black background of space are several yellow and red dots, which are background galaxies.
November 17, 2025 at 12:31 AM
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Image of Arp 12, also known as NGC 2608, from Halton Arp's Atlas of Peculiar Galaxies (1966).

In the original catalog it was in the category: Spiral galaxies - Split arms. NGC 2608 is a barred spiral galaxy in the constellation Cancer.
Source
A grainy, black and white image of a barred spiral galaxy. It has a central core and vertical bar structure. The arms are somewhat squished, so the galaxy appears oval-shaped, longer than it is tall. The arm that curves from 6 o'clock to 12 o'clock forks into three near its end. Several white dots, which are stars, are seen on the black background.
November 16, 2025 at 12:31 PM
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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.
Source
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.
November 16, 2025 at 12:31 AM
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Hubble image of Arp 81, also known as NGC 6621 and NGC 6622.

A recent encounter between NGC 6621 (right) and NGC 6622 (left) pulled a long tail out of NGC 6621 that wraps behind the galaxy.

Credit: NASA, ESA, STScI
Source
Two galaxies that are in the process of merging sit side by side. The first, to the left, shows a vertical bar structure, surrounded by a haze of older, yellow stars. The galaxy's core is partially obscured by a swirl of dark brown dust. The galaxy overlaps with its companion to the right, and there is a small area of blue star clusters where the two galaxies meet. The galaxy on the right is a disturbed spiral galaxy. The remnants of two spiral arms form a backward S-shape. The right arm continues into a large fish-hook shaped tidal tail. The tail trails off to the right, then curves over the spiral galaxy and extends all the way to its companion galaxy on the left. The tail is dotted with blue star clusters. The portion of the tail that curves upwards, the bend in the fish hook, is partially obscured with brown clumps of dust.
November 15, 2025 at 12:31 PM
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Hubble Space Telescope image of Arp 25, also known as NGC 2276.

The lopsided galaxy has a core offset to the upper left and a spiral arm separated from the others. It is interacting with a nearby galaxy, just out of frame.

Credit: NASA, ESA, STScI, P. Sell
Source
Against the black background of space, which has distant stars and galaxies scattered across, is a large spiral galaxy filled with streaks of blue and pink. The galaxy has warped spiral arms that wrap clockwise around its bright yellow core. Toward the upper right, one of its arms appears to be breaking away from the rest of the galaxy.
November 15, 2025 at 12:31 AM
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Image of Arp 91, also known as NGC 5953 and NGC 5954, from Halton Arp's Atlas of Peculiar Galaxies (1966).

In the original catalog it was in the category: Spiral galaxies - Large, high surface brightness companions. A tidal tail connects the pair.
Source
A grainy, black and white image of a pair of interacting spiral galaxies. The galaxy in the center has a face-on disk with a brighter center. To the left is its companion galaxy. The disk of this galaxy is seen at an angle, tilted so that it appears to be an oval rather than a circle. The spiral structures in its disk are dotted with star clusters. At the bottom edge of this galaxy, the end of a spiral arm or a tidal tail appears to extend to the right, connecting to the side of its companion.
November 14, 2025 at 12:31 PM
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GALEX and SDSS image of Arp 297, also known as NGC 5755, NGC 5753, NGC 5754 and NGC 5752.

The left image is in ultraviolet light. The right image is in visible light.

The upper and lower galaxy pairs are at different distances.

Credit: Fig. 13 from Smith et al. 2010.
Source
A two-panel image. The left panel is labeled Arp 297 GALEX. A scale bar marks 1 arcminute, which is about 1/8 the width of the frame. The panel shows a low-res image in shades of yellow and blue. There are four small galaxies, arranged in two pairs, on a field of stars. The bottom pair is a large face-on barred spiral galaxy and a smaller edge-on disk galaxy. The spiral has a bright, pale yellow, circular core. Two spiral arms circle around the core. One thinner arm emerges in the outer part of the galaxy at about 9 o'clock and circles counterclockwise to 12 o'clock, intersecting the companion galaxy to the left. The smaller companion galaxy is yellow and oval-shaped. The upper pair is two nearly face-on spiral galaxies. The bottom galaxy of the pair has a yellow core and bar with two faint spiral arms that make an S-shape. The top galaxy of the pair appears as a bluish grey circle. The right panel is labeled Arp 297 SDSS and has a similar 1 arcminute scale bar. It shows the same galaxies at the same scale and is higher resolution. The bottom pair of galaxies appears in shades of pale yellow. The spiral appears similar to the GALEX image, but the center of the galaxy has a prominent bar structure, which was not seen by GALEX. The top pair of galaxies also is similar to the GALEX image, but shows more detail. The bottom galaxy of the pair is in shades of white and pale blue. The top galaxy has a bright core and barely discernible spiral arms and is in shades of yellow.
November 14, 2025 at 12:31 AM
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Image of Arp 302, also known as UGC 9618 or VV 340, 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 pair is beginning to interact.
Source
A grainy, black and white image of a pair of spiral galaxies. The lower galaxy is seen face-on. It has a bright center that transitions into a series of loosely-wound spiral arms, looking something like a cinnamon roll. The arms are dotted with star clusters . The upper galaxy is seen edge on. It has a somewhat puffy disk, seen as a wide, vertical line. Together, the two galaxies look like an exclamation point. In the middle of the frame, where the two galaxies appear to touch, is a bright foreground star seen as a large dot. A few white dots, which are stars, are seen on the black background.
November 13, 2025 at 12:31 AM