ESO 137-001

Lore & Background

ESO 137-001 was discovered by Ming Sun in 2005. As the galaxy moves toward the center of the galaxy cluster Abell 3627 at 1900 km/s, it is stripped by hot intergalactic gas at 100 million Kelvin, a process called ram pressure stripping (RPS). This stripping creates a 260,000 light-year long tail where star formation occurs. The galaxy has a low amount of HI regions, with a total mass of 3.5 × 10^8 solar masses, only 10% of which is located in the main disk of ESO 137-001.

Reader's Guide

The stripping of gas is thought to have a significant effect on the galaxy's development. It removes cold gas from the galaxy, shutting down the formation of new stars in the galaxy, and changing the appearance of inner spiral arms and bulges because of the effects of star formation. This makes ESO 137-001 a key example of how ram pressure stripping can transform a spiral galaxy in a dense cluster environment, providing insight into the fate of galaxies that fall into cluster centers.

Did You Know?

• ESO 137-001 is also called the Jellyfish Galaxy.
• It moves toward the center of Abell 3627 at 1900 km/s.
• Its tail extends 260,000 light-years and hosts star formation.
• Only 10% of its total HI mass is in the main disk.

A Single Thread in an Enormous Tapestry

ESO 137-001 exists as one entry among an almost incomprehensible population of galaxies. Current estimates place the number of galaxies in the observable universe at well over two trillion, a figure so vast that any individual object becomes a statistical grain. Within that ocean, structure organizes itself into nested groupings: the Local Group contains roughly fifty-one galaxies, while the broader Local Supercluster swells to around one hundred thousand. ESO 137-001, like the vast majority of its peers, does not enjoy the distinction of being a naked-eye object visible to keen observers on a dark, high-altitude night under stable skies. It is, instead, a member of the larger census—identified by its systematic designation rather than a popular name, and catalogued alongside millions of others in the ongoing effort to map what lies beyond the Milky Way's immediate neighbourhood.

The Slow Art of Cataloguing the Sky

Systematic attempts to enumerate galaxies only gained real momentum in the 1960s. The Catalogue of Galaxies and Clusters of Galaxies recorded twenty-nine thousand four hundred and eighteen objects, while the Morphological Catalogue of Galaxies, aiming for completeness above photographic magnitude fifteen, listed thirty thousand six hundred and forty-two. By the 1980s, the Lyons Groups of Galaxies had organized four hundred and eighty-five groups containing nearly four thousand member galaxies. The twenty-first century brought a different scale: Galaxy Zoo, launched in July 2007, has since classified more than one million galaxy images drawn from the Sloan Digital Sky Survey, the Hubble Space Telescope, and the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey. ESO 137-001 sits within this layered heritage of ever-expanding inventories, a single data point in a project that has never truly finished.

Beyond the Poetic Name

Astronomers distinguish between galaxies that carry a memorable common name and those known only through a catalogue entry, a set of coordinates, or a systematic designation. The well-known named galaxies—those recognized by something other than a list entry—form a small, celebrated subset. ESO 137-001 belongs to the far larger group: an object whose identity is carried by its designation in a survey catalogue rather than by a title that has entered popular astronomy. This is not a mark of lesser importance; it simply reflects the reality that the overwhelming majority of the two-trillion-plus galaxies in the observable universe will never acquire a nickname. Their significance lies in the data they provide, their position within the Local Supercluster's hundred-thousand-galaxy structure, and their contribution to the statistical picture of how galaxies distribute themselves across space.

The Burden of Confirmation

The history of galaxy discovery is littered with objects whose claimed redshifts were later disputed, unreplicated, or based on misidentified spectral lines. MACS0647-JD, UDFy-38135539, A1689-zD1, and numerous others have been excluded from definitive lists because spectroscopic confirmation never materialized. In 1999, STIS 123627+621755 was misassigned a redshift due to an oxygen line being mistaken for hydrogen. Even in 1975, 3C 123 was incorrectly placed at a redshift far from its true value. These episodes underscore the rigorous standard that separates a verified entry in a catalogue from a tentative detection. ESO 137-001, like any galaxy whose properties are recorded in systematic surveys, represents an object that has passed through the necessary observational checks to earn its place in the record rather than remaining a disputed footnote in a timeline of firsts.