Scientists from the University of Bonn in Germany have discovered the longest gas tail linked to the gravitational stripping of materials from a galaxy. The bright object is part of the Zwicky 8338 cluster, which is about 860 million light-years from us.
The gas flow resembles a comet, as it shows two components: a hot tail made mostly of hydrogen and helium, and a cool head, made of other elements and thus considered “metal-rich.” It extends for at least 228,000 light-years, although some preliminary indications could hint at a size of almost half a million light-years.
The galaxy associated with the tail, named CGCG254-021, is an old elliptical galaxy. It has a mass comparable to Andromeda’s, and although it’s not forming any new stars, it used to have five times the star formation rate of the Milky Way. The Milky Way tends to produce, on average, a star the mass of our Sun every year.
The structure indicates a more active past for the now-aged galaxy. “We think that the tail is caused by an infalling galaxy into the galaxy cluster,” Gerrit Schellenberger, co-author of the study with Thomas Reiprich, told IFLScience. “If it turns out that the galaxy is part of a small galaxy group, this would be a merger.”
The tail was observed by Chandra, NASA’s X-ray Observatory. The material between galaxies, the so-called intracluster medium (ICM), is superheated into a plasma that reaches temperatures between 10 million to 100 million kelvins. The ICM is heated by the gravitational interactions, which over time pass on to the plasma enough energy to shine brightly in X-rays. Galaxy tails are created when the cool gas from a galaxy interacts with the hot ICM.
This tail is not the first one observed to have such an unusual size. A similar display was detected in 2006 associated with the Norma Cluster, one of the groups of galaxies more closely associated with the Great Attractor. The Norma Cluster shows two tails of similar length to CGCG254-021, but 20 times fainter.
Follow-up studies of these types of objects could hopefully explain how elements other than hydrogen come to be present in the ICM. “We think that the ICM metal enrichment by galaxy gas stripping processes is a valid scenario, but we can neither confirm, nor exclude it with our data, although the idea is supported by simulations,” Schellenberger added. “The exact contribution compared to AGN feedback or supernovae-driven galactic winds needs to be studied in more detail with a deeper observation of this object.”
The research is published in the journal Astronomy & Astrophysics.
