The Helix Galaxy is a lenticular polar ring galaxy located approximately 48.2 million light-years away in the constellation Ursa Major (the Great Bear). It has an apparent magnitude of 11.3 and an apparent size of 4.6 by 2.5 arcminutes. It is catalogued as NGC 2685 in the New General Catalogue and Arp 336 in Halton Arp’s Atlas of Peculiar Galaxies.
NGC 2685 is a rare galaxy. Like all polar ring galaxies, it has an outer ring of stars and gas that rotates over the galaxy’s poles. The polar rings are believed to have formed because of gravitational interaction between two galaxies.
The rings may be composed of captured debris stripped from a passing galaxy or they may be what is left of a smaller galaxy itself if it collided perpendicularly to the larger galaxy’s plane of rotation. The captured material was pulled out in strands and is strung out in loops. It appears like an encircling ring. The perpendicular rings pass in front of the galactic disk and are visible in long-exposure images of the galaxy.
The very unusual galaxy NGC 2685, also known as the Helix Galaxy, is located about 40 million light-years away in the constellation Ursa Major. This image was captured by the Gemini North telescope, one half of the International Gemini Observatory, operated by NSF NOIRLab, which is funded by the U.S. National Science Foundation. NGC 2685 is a peculiar lenticular galaxy known as a polar ring galaxy. A ring of gas, stars, and dust orbits NGC 2685 perpendicular to the flat plane of the host galaxy. This odd crossing of planes is believed to be evidence of galaxy interactions, mergers, or tidal accretion events. Current research suggests that the present structure of NGC 2685 was formed when it captured material from another galaxy, which was strung out into an encircling ring. This galaxy is one of our closest known polar ring galaxies and is therefore one of the easiest of its kind to study. Image credit: International Gemini Observatory/NOIRLab/NSF/AURA/L. Bassino Image processing: J. Miller (Gemini Observatory/NSF’s NOIRLab), M. Rodriguez (Gemini Observatory/NSF’s NOIRLab), & M. Zamani (NSF’s NOIRLab) (CC BY 4.0)
The Helix Galaxy is around 61,900 light-years across. It was one of the first galaxies to be identified as a polar ring galaxy. Observations have shown that its rotating ring structure is very old and stable.
NGC 2685 is classified as a lenticular galaxy because it contains a large-scale disk and a prominent bulge, but no spiral arms. The added classification of ring galaxy is due to the dust, gas and stars orbiting in rings that are perpendicular to the galaxy’s flat plane.
The Helix Galaxy is classified as a Type II Seyfert galaxy. It has an active galactic nucleus (AGN) and a core that appears bright both at visible and infrared wavelengths.
The northeastern side of the elongated central region is obscured by dark dust lanes and dotted with star-forming regions. These dust lanes and H II regions are absent on the southwestern side. The dust lanes resemble a helical structure, which is why NGC 2685 is popularly known as the Helix Galaxy.
NGC 2685 (Helix Galaxy) imaged by W4SM with 17″ PlaneWave astrograph. Credit: Wikimedia Commons/W4sm astro (CC BY-SA 4.0)
Observations with Hubble’s Wide Field Planetary Camera 2 have allowed astronomers to resolve around 800 stars in the galaxy’s polar rings. Many of these stars are hot blue supergiants in young star clusters. The age of the youngest detected stars in the rings is about 9 million years.
Observations with the Galaxy Evolution Explorer (GALEX) and the Infrared Array Camera (IRAC) on the Spitzer Space Telescope in the 2010s have revealed that the Helix Galaxy has a relatively low star formation rate with respect to the neutral atomic hydrogen (HI) observed.
A 2025 study of the evolutionary path of polar-ring galaxies (PRGs) proposed that the Helix Galaxy represented the intermediate stage in the evolution of these objects. The galaxy has a lower star formation rate than NGC 3718 in Ursa Major, which represents the initial stage of PRG evolution, but a higher rate than NGC 4262 in Coma Berenices, which represents the final stage. The ring and the host in NGC 2685 have a similar age, and star formation is much higher in the ring regions.
NGC 2685 is an interesting polar ring galaxy in the constellation Ursa Major. It is also called the Helix Galaxy or the Pancake Galaxy. It has a set of unusual whorls, or helical filaments, surrounding the central spindle of a relatively normal S0 galaxy. Sometimes classified as SB0(pec), NGC 2685 is odd enough to appear as number 336 in Arp’s Atlas of Peculiar Galaxies. Polar ring galaxies are dynamically peculiar, having a ring of gas, stars and dust orbiting in a plane almost perpendicular to the normal flat plane of the host galaxy, that is, they contain two separate velocity systems whose axes are perpendicular. The most popular view says that such galaxies are the result of an interaction, up to and including a complete merger with another galaxy. NGC 2685 also shows weak emission lines in the optical, and none in the infrared, making it an atypical member of the class of active galaxies called LINERS. The present picture is a color composite of CCD images from the 0.9-meter telescope of the Kitt Peak National Observatory, near Tucson, Arizona, taken in November 1998. Image credit: NOIRLab/AURA/NSF (CC BY 4.0)
Facts
NGC 2685 was discovered by the German astronomer Wilhelm Tempel on August 18, 1882. It is one of the two nearest polar ring galaxies to Earth, along with NGC 660 in the constellation Pisces, which lies 45 million light-years away.
The morphology of NGC 2685 has frequently been a target of studies. In 1961, American astronomer Allan Sandage referred to the galaxy as a “spindle” because of the helical filaments that surround the main body. He noted that the Helix Galaxy was “perhaps the most peculiar galaxy in the Shapley-Ames Catalog.”
In 1978, Paul L. Schlechter and James E. Gunn said that NGC 2685 is flattened when the filaments are ignored and therefore an edge-on lenticular galaxy (S0). They observed the galaxy with the 5-m Hale Telescope at the Palomar Observatory in California. The flattened shape has led to the nickname the Pancake Galaxy.
The Helix Galaxy, credit: Sloan Digital Sky Survey (CC BY 4.0)
NGC 2685 is sometimes also called the Spindle Galaxy. It is not to be confused with the Spindle Galaxy (NGC 3115) in the constellation Sextans and the Spindle Galaxy (NGC 5866, Messier 102) in Draco. The other two Spindle galaxies are both lenticular galaxies, but they are not ring galaxies. Unlike the Helix Galaxy, they can be spotted in a small telescope.
The Helix Galaxy has a popular namesake, the Helix Nebula (NGC 7293), located in the constellation Aquarius. The two objects are completely unrelated. The Helix Nebula is one of the brightest and largest planetary nebulae in the night sky, along with the Dumbbell Nebula (Messier 27) in Vulpecula and the Ring Nebula (Messier 57) in Lyra. It formed when an evolved central star expelled its outer gaseous layers in a late phase of its life, before becoming a white dwarf. The nebula’s name comes from its appearance in earlier images, as well as to the resemblance of its spiral-like structure to that of a DNA helix. The Helix Nebula is visible in binoculars on a clear night.
NGC2685 is an unusual lenticular galaxy of type S0(pec), in the constellation Ursa Major. It shows two axes of symmetry as well as an encircling ring. KPNO 4-meter Mayall telescope, 1975. Credit: NOIRLab/NSF/AURA (CC BY 4.0)
Location
The Helix Galaxy lies in the region of the Great Bear’s head. The nearest relatively bright star is the yellow giant Muscida (Omicron Ursae Majoris, mag. 3.35), which marks the Great Bear’s snout. The galaxy appears along the imaginary line extended from Phecda (Gamma Ursae Majoris) in the Big Dipper through the fainter Upsilon Ursae Majoris.
NGC 2685 is best observed in large telescopes (16-inch and larger) at high magnification. These will reveal an elongated streak of light with a brighter centre.
The location of the Helix Galaxy (NGC 2685), image: Stellarium
The best time of the year to observe the Helix Galaxy and other deep sky objects in Ursa Major is during the month of April, when the constellation appears high above the horizon in the early evening. For observers in the northern hemisphere, the Great Bear is visible throughout the year.
At declination +58° 44 44’, the Helix Galaxy never rises for observers south of the latitude 30-31° S.
Helix Galaxy – NGC 2685
| Constellation | Ursa Major |
| Object type | Lenticular and polar ring galaxy |
| Morphological type | (R)SB0^+ pec |
| Right ascension | 08h 55m 34.7027817011s |
| Declination | +58° 44′ 03.876540090″ |
| Apparent magnitude | 11.3 |
| Apparent size | 4.6’ x 2.5’ |
| Distance | 48.2 ± 3.4 million light-years (14.79 ± 1.05 megaparsecs) |
| Redshift | 0.002945 |
| Size | 61,900 light-years (18,980 parsecs) |
| Names and designations | Helix Galaxy, Pancake Galaxy, NGC 2685, Arp 336, PGC 25065, LEDA 25065, UGC 4666, MCG +10-13-039, CGCG 288-012, IRAS F08516+5855, 2MASX J08553474+5844038, PRC A-3, SDSS J085534.70+584403.8, TC 706, UZC J085534.6+584403, EQ 0851+589, Z 288-12, Z 0851.7+5855, 2XMM J085534.4+584404, Gaia DR2 1037829781374251392, Gaia DR3 1037829781374251392 |