The Comet Galaxy is a spiral galaxy located approximately 3.3 billion light-years away in the southern constellation Sculptor. It is a member of the galaxy cluster Abell 2667. The late-type spiral galaxy is catalogued as EQ J235144-260358. It was discovered with the Hubble Space Telescope (HST) in 2007.
The Comet Galaxy is a jellyfish galaxy. Like the prototypical Jellyfish Galaxy (ESO 137-001) in the constellation Triangulum Australe, it has extended trails of bright blue knots stretching from its optical disk, with fainter long, blue wisps and filaments and diffuse ionized gas appearing along the same trail. This indicates that the galaxy’s unusual structure is the result of ram pressure stripping as the galaxy falls towards the centre of the dense cluster Abell 2667. Astronomers have estimated a dynamical age of 50 – 150 million years for the trails.
EQ J235144-260358 has been nicknamed the Comet Galaxy because it speeds through the cluster Abell 2667 at a velocity of 1,000 km/s. Like a comet, it has a tail, one that extends for 600,000 light-years.
Comet Galaxy by the Hubble Space Telescope (HST), cropped from original. Image credit: NASA, ESA, Jean-Paul Kneib (Laboratoire d’Astrophysique de Marseille) (PD)
The processes that produce tails in comets and stripped galaxies are similar. The tail of the Comet Galaxy is the result of charged particles stripping the galaxy’s gas. The tails of comets in the solar system are produced by the solar wind of charged particles pushing ionized gas from the comets to produce gas tails.
Ram pressure stripping is a process that occurs in dense environments, where the drag force of the surrounding hot gas strips away the interstellar gas in a galaxy as the galaxy moves through the harsh environment of the cluster. The process can ultimately severely affect a galaxy’s ability to form new stars and transform a spiral galaxy into a gas-poor elliptical galaxy with an old population of red stars. The whole process takes about a billion years. As the galaxy’s gas is stripped away, it forms a trail that traces the galaxy’s trajectory through the dense intracluster medium.
Ram pressure has only affected the outer regions of the Comet Galaxy, but not the galaxy’s central region where the starburst is taking place. It has stripped stars and ionized gas from the galaxy’s disk and produced the stellar wisps and blue knots visible in the Hubble image of the galaxy. The blue knots have a physical size comparable to that of ultra compact dwarf galaxies.
The Comet Galaxy is larger than the Milky Way and Andromeda galaxies. Based on an apparent size of 10.8 arcseconds and a distance of 3.3 billion light-years, the galaxy has a diameter of 170,000 light-years (52.2 kpc). In comparison, the Andromeda Galaxy has an isophotal diameter of 152,000 light-years and our Milky Way is 87,400 light-years across.
Abell 2667, the home of the Comet Galaxy, is one of the most luminous clusters of galaxies in the X-ray band. The cluster is a well-known gravitational lens. A giant arc that appears 14 arcseconds from the brightest cluster galaxy is in fact a distant background galaxy multiplied into three images, two of which are merged. Astronomers have identified the source galaxy as a normal disk galaxy with a bright central bulge and tightly wrapped spiral arms. While it appears in the same field of view as the members of Abell 2667, the lensed galaxy lies at a much greater distance. Without the gravitational lensing, it would likely not be detectable by Hubble.
While looking at the galaxy cluster Abell 2667, astronomers found an odd-looking spiral galaxy (shown here in the upper left hand corner of the image) that ploughs through the cluster after being accelerated to at least 3.5 million km/h by the enormous combined gravity of the cluster’s dark matter, hot gas and hundreds of galaxies. Credit: NASA, ESA, and J. Kneib (Laboratorie d’Astrophysique de Marseille) (PD)
Facts
The Comet Galaxy was discovered by an international team of astronomers led by Luca Cortese of the School of Physics and Astronomy, Cardiff University, UK, in 2007. The team reported the discovery in a study published in the Monthly Notices of the Royal Astronomical Society in March 2007. They noted that the Comet Galaxy was one of the brightest members of Abell 2667, both in the optical and near-infrared band.
Cortese et al. found the galaxy by combining optical, near and mid-infrared and radio observations with the Wide Field Planetary Camera 2 (WFPC2) on the Hubble Space Telescope (HST), the Infrared Spectrometer and Array Camera (ISAAC) on the Very Large Telescope (VLT), the Multiband Imaging Photometer (MIPS) on the Spitzer Space Telescope, combined with data obtained during the National Radio Astronomy Observatory (NRAO) VLA Sky Survey (NVSS) and with the Advanced CCD Imaging Spectrometer (ACIS) on the Chandra X-ray Observatory.
The team reported that the galaxy had a disturbed morphology, with strong evidence of stripping in its optical disk and a strong burst of star formation in the centre. The astronomers noted that the galaxy was a rare example of a luminous infrared galaxy (LIRG) located in a dense galaxy cluster. The high rate of star formation was triggered by tidal interaction with other cluster members.
This infrared image was taken by NASA’s Spitzer Space Telescope and shows a part of the galaxy cluster Abell 2667. The “Comet Galaxy” is the bright red object seen to the left of the cluster center. Also seen in the image is a rare giant infrared arc. The banana-shaped arc corresponds to the magnified and distorted image of a distant galaxy that lies behind the cluster’s core. Image credit: NASA/JPL-Caltech (PD)
Location
The Comet Galaxy and the cluster Abell 2667 lie in the faint southern constellation of Sculptor. They appear south of the midpoint of the imaginary line connecting Diphda in the constellation Cetus and Fomalhaut in Piscis Austrinus. Diphda and Fomalhaut can be found using the bright stars of the Great Square of Pegasus in the constellations Pegasus and Andromeda.
At declination -26°, the Comet Galaxy never rises above the horizon from locations north of the latitude 64° N. The galaxy is too faint and small to be observed in amateur telescopes.
Comet Galaxy location, image: Stellarium
Comet Galaxy – EQ J235144-260358
| Constellation | Sculptor |
| Object type | Irregular spiral galaxy |
| Morphological type | dIrr |
| Right ascension | 23h 51m 44.03s |
| Declination | −26° 03′ 59.6″ |
| Apparent magnitude (B) | 18.642 |
| Apparent magnitude (R) | 18.551 |
| Apparent size | 0.18′ × 0.15′ |
| Distance (comoving) | 3,250 ± 227.7 million light years (996.6 ± 69.8 megaparsecs) h−10.6774 |
| Distance (light-travel) | 2.777 gigalight-years (0.8514 gigaparsecs) h−10.6774 |
| Redshift | 0.2265 |
| Heliocentric radial velocity | 67,753 ± 89 km/s |
| Galactocentric velocity | 67,778 ± 89 km/s |
| Size | 170,000 light-years × 142,000 light-years (52.2 × 43.5 kiloparsecs) |
| Mass (stellar) | 3.8 × 108 M☉ |
| Names and designations | Comet Galaxy, LEDA 3234374, PGC 3234374, EQ J235144-260358, WISEA J235144.05-260357.9, 2dFGRS TGS132Z144 |