The Porpoise Galaxy (NGC 2936) is an irregular galaxy located in the constellation Hydra. It is also known as the Penguin Galaxy. The interacting galaxy lies at a distance of 352 million light years from the Sun and has an apparent magnitude of 12.85. It was imaged by the James Webb Space Telescope (JWST) in 2024.
Located in the region of the sky between the bright Regulus in Leo and Alphard in Hydra, NGC 2936 is currently in the process of interacting with the elliptical galaxy NGC 2937. As a result of the interaction, the larger galaxy’s shape has been severely distorted into one that resembles a porpoise or a penguin.
The interacting pair is sometimes called the Penguin and the Egg. The two galaxies are in an early stage of a merger.
This image shows the two galaxies interacting. NGC 2936, once a standard spiral galaxy, and NGC 2937, a smaller elliptical, bear a striking resemblance to a penguin guarding its egg. This image is a combination of visible and infrared light, created from data gathered by the NASA/ESA Hubble Space Telescope Wide Field Planetary Camera 3 (WFC3). Image: NASA, ESA and the Hubble Heritage Team (STScI/AURA) (CC BY 3.0)
Due to the tidal interaction with the neighbouring galaxy, the dust and gas are being drawn out from the centre of NGC 2936. As they become compressed, they trigger the formation of new stars. The Simbad database lists over 20 HII regions in the galaxy. Astronomers believe that the Penguin produces 100 – 200 stars per year (compared to the Milky Way’s 6-7 stars per year).
The star-forming regions of NGC 2936 appear as bluish knots in the heavily distorted spiral arms that stretch in the direction of the smaller elliptical galaxy. The strong emission lines from the spiral arm indicate the presence of massive young stars that are ionizing the surrounding gas.
The reddish dust that used to be in the galaxy’s centre has mostly been expelled during the encounter, and what was once the galactic bulge now marks the eye of the porpoise.
Only a few hundred million years ago, NGC 2936 was likely a regular spiral galaxy with a flat spiral disk. In another billion years, the galaxy and its companion will merge into a single larger galaxy. A study published in 2019 suggests that the first pericenter passage between the galaxies occurred only about 50 ± 25 million years ago.
The neighbour, NGC 2937, contains very little dust and gas and its stars are mostly old. While the orbits of its stars may be affected by the encounter with NGC 2936, the effect of the interaction is not apparent.
Even though NGC 2937 appears much smaller than the Porpoise Galaxy, the elliptical galaxy has a similar mass to its larger neighbour. If it were much less massive, the pair would have likely already merged and the smaller Egg would have been absorbed into the larger Penguin.
Facts
NGC 2936 and NGC 2937 were discovered by the German astronomer Albert Marth on March 3, 1864.
The interacting pair is catalogued as Arp 142 in Halton Arp’s Atlas of Peculiar Galaxies. Arp 142 is listed as a “galaxy triplet” and includes the blue galaxy appearing next to NGC 2936, catalogued as UGC 5130 or PGC 1237172.
UGC 5130 is either an edge-on spiral or an irregular galaxy located 230 million light-years away. It appears in the same line of sight as the Penguin and the Egg, but is more than 100 million light-years closer to the Sun. It is not physically related to the colliding pair.
The Penguin Galaxy was imaged by the Hubble Space Telescope (HST) on June 20, 2013. Captured by the Wide Field Camera 3, the image showed the effects of the interaction between the galaxy and its smaller neighbour.
In 2024, NGC 2936 and NGC 2937 were captured by the James Webb Space Telescope (JWST). The images taken by Webb’s NIRCam and MIRI instruments marked the space telescope’s second year of science. They revealed new details of the galactic merger in infrared light and showed many more distant galaxies that lie in the background. Webb’s infrared instruments peeked through the dust in the galaxy to show new star forming regions that are invisible in optical wavelengths.
The distorted spiral galaxy at the centre, the Penguin, and the compact elliptical galaxy at the left, the Egg, are locked in an active embrace. A new near- and mid-infrared image from the James Webb Space Telescope
shows that their interaction is marked by a faint upside-down U-shaped blue glow. This gravitational shimmy also remade the Penguin’s appearance. Its coiled spiral arms unwound, and gas and dust were pulled in an array of directions, like it was releasing confetti. It is rare for individual stars to collide when galaxies interact (space is vast), but the galaxies’ mingling disrupts their stars’ orbits.Today, the Penguin’s galactic centre looks like an eye set within a head, and the galaxy has prominent star trails that take the shape of a beak, backbone, and fanned-out tail. A faint, but prominent dust lane extends from its beak down to its tail. The oval Egg is filled with old stars, and little gas and dust, which is why it isn’t sending out ‘streamers’ or tidal tails of its own and instead has maintained a compact oval shape. Image credit: NASA, ESA, CSA, STScI (CC BY 4.0)
The brightest star in the Porpoise Galaxy is catalogued as USNOA2 0900-06460021.
Location
NGC 2936 lies in the faint constellation Hydra. The galaxy appears west of the imaginary line connecting Regulus, the brightest star in Leo, and Alphard, the luminary of Hydra.
At declination +02° 45’, the celestial Penguin is visible from any location on Earth for at least part of the year. The best time to observe the galaxy and other deep sky objects in Hydra is during the month of April, when the constellation rises higher above the horizon in the early evening.
The location of the Porpoise Galaxy (NGC 2936), image: Stellarium
Porpoise Galaxy (Penguin Galaxy) – NGC 2936
| Constellation | Hydra |
| Object type | Interacting galaxy |
| Type | Irregular (Irr) |
| Right ascension | 09h 37m 44.1399551712s |
| Declination | +02° 45′ 39.173273352″ |
| Apparent magnitude | 12.85 |
| Angular size | 1.280 x 0.563 arcminutes |
| Absolute magnitude | -22.4 |
| Distance | 352 million light-years (108 megaparsecs) |
| Redshift | 0.02331 ± 0.00013 |
| Heliocentric radial velocity | 6989 ± 38 km/s |
| Galactocentric velocity | 6844 ± 39 km/s |
| Size | 164.839 kilolight-years (50.54 kiloparsecs) |
| Names and designations | Porpoise Galaxy, Penguin Galaxy, Penguin and the Egg, NGC 2936, UGC 5130, VV 316a, SDSS J093744.14+024538.9, MCG+01-25-006, IRAS 09351+0259, 2MASX J09374413+0245394, ECO 4865, LEDA 27422, PSCz Q09351+0259, QDOT B0935091+025903, RESOLVE rs100, Gaia DR2 3847693975935370112, Gaia DR3 3847693975935370112, UZC J093744.3+024541, Z 35-15, Z 0935.1+0258 |
Images
Webb’s mid-infrared view of interacting galaxies Arp 142 seems to sing in primary colours. The background of space is like a yawning darkness speckled with bright, multi-coloured beads.This image was taken by MIRI, the telescope’s Mid-InfraRed Instrument, which astronomers use to study cooler and older objects, dust, and extremely distant galaxies.Here, the Egg appears as an exceptionally small teal oval with gauzy layers. Mid-infrared light predominantly shows the oldest stars in the elliptical galaxy, which has lost or used up most of its gas and dust. Image credit: NASA, ESA, CSA, STScI (CC BY 4.0)
The Porpoise Galaxy imaged by James Webb’s NIRCam instrument. Image credit: NASA, ESA, CSA, STScI (CC BY 4.0)
NGC 2936 and NGC 2937 by NASA’s Hubble Space Telescope, image credit: NASA/ESA/Hubble Team/Kevin M. Gill (CC BY 2.0)