This phenomenon has been identified as the longest known tail trailing a galaxy group
Astronomers are observing a cluster of galaxies, identified as NGC 4839, plunging headlong into the Coma galaxy cluster, producing an extraordinary, superheated gas tail in its wake. This phenomenon has been identified as the longest known tail trailing a galaxy group, providing unique insights into the growth and development of galaxy clusters among the universe’s largest structures.
The Intricate Universe: Clusters and Groups of Galaxies
NGC 4839 is a galaxy group—a gravitational congregation of around 50 galaxies or less. By contrast, galaxy clusters are significantly larger, potentially comprising hundreds or thousands of individual galaxies, enveloped by vast expanses of scorching gas that can be best studied using X-ray technology.
NGC 4839: A Spectacular Entry into the Coma Cluster
Located near the Coma galaxy cluster’s edge, NGC 4839 is making a grand entry into one of the universe’s most extensive known clusters, roughly 340 million light-years away. This motion creates a spectacular tail behind the galaxy group, formed as the hot gas within NGC 4839 is stripped off due to its collision with the cluster’s gas.
The Remarkable Coma Cluster: A Spectacular X-ray View
ESA’s XMM-Newton X-ray observatory and the Sloan Digital Sky Survey have combined to provide an intriguing image of the Coma galaxy cluster, with the NGC 4839 group situated in the lower right. The head of NGC 4839’s tail, visible in the Chandra image, houses the group’s brightest galaxy and densest gas.
Stretching an incredible 1.5 million light-years, hundreds of thousands of times the distance from the Sun to the nearest star, NGC 4839’s tail is the longest ever observed behind a galaxy group. This dazzling spectacle offers astronomers a unique opportunity to study the tail’s physics before it merges with the Coma Cluster’s hot gas.
Supersonic Speed: The Sonic Boom of the Universe
Analysis of the Chandra data has led researchers to discover a shock wave, akin to a sonic boom from a supersonic jet. The discovery indicates NGC 4839’s speed of about 3 million miles per hour as it traverses through the galaxy cluster.
The researchers also analyzed the turbulence in the tail’s gas, finding only a mild degree, which suggests low heat conduction in NGC 4839. Additionally, potential evidence of Kelvin-Helmholtz instabilities, caused by varying speeds of adjacent moving gas or fluid layers, suggests a weak magnetic field or low viscosity in the tail’s gas.
A New Milestone: The Tail Length Record Holder
Earlier observations had estimated NGC 4839’s tail to stretch at least one million light-years. However, new Chandra data reveal its staggering length of 1.5 million light-years—a new record.
The groundbreaking research, led by Stephen Walker of the University of Alabama at Huntsville, was presented at the 242nd meeting of the American Astronomical Society. A detailed paper has also been published online, further outlining these fascinating findings.
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