A Tail of Galactic Proportions
Astronomers using NASA’s Chandra X-ray Observatory have spotted a galaxy with a ribbon of hot gas trailing along behind it as it plows through a cloud of intergalactic gas. In this composite image, which shows X-ray data in blue and visible light from the Isaac Newton Group of Telescopes in yellow, the subject galaxy is at right center, with its blue tail above. That tail is extraordinary in size, stretching along for at least 250,000 light-years behind the galaxy, which is in motion towards the bottom of the frame.
This drama is unfolding about 700 million light-years away in the galaxy cluster Zwicky 8338, located in the direction of the constellation Hercules. The image is about 700 light-years across, and shows many of the cluster’s galaxies. The galaxy sporting the tail is known as CGCG254-021, and may itself even be a group of galaxies dominated by this large spiral. It lies slightly more than one million light-years from the center of Zwicky 8338.
The tail contains gas that was stripped from the home galaxy by the pressure exerted from its rapid motion through the galaxy cluster. Containing gas at temperatures of about 10 million degrees, the tail is considerably cooler than its 30 million degree surroundings. The “head” of the tail, the bright spot just above the galaxy itself, appears to be cooler and richer in elements heavier than helium compared to the rest of the tail. There is also a distinct separation between the galaxy and its tail, possibly indicating that the galaxy has been completely stripped of all of its gas. Infrared observations seem to bolster this argument, as there is no indication of new star formation in CGCG254-021. The same infrared data shows that this galaxy has the highest mass in the entire cluster, and had by far the highest rate of new star formation in the cluster in the recent past.
“This tail is a vivid example of how dynamic galaxy clusters are, as we may be seeing the transformation of a galaxy as it moves through the cluster,” said Gerrit Schellenberger of the University of Bonn in Germany, who led the study. “Also, the material in the tail includes not only hydrogen but heavier elements, and could spawn a new generation of stars trailing behind the galaxy.”
Image credit: X-ray: NASA/CXC/University of Bonn/G. Schellenberger et al; Optical: INT