XMM-Newton image of a giant cometary cloud in the galaxy cluster Abell 3266. Image: University of Maryland, Baltimore County (UMBC) Astronomers working with the orbiting X-ray observatory XMM-Newton have found a huge hot comet-like ball of gas moving through a cluster of galaxies at 750 km per second.

The gas ball is about three million light years across, or five billion times the size of our Solar System and is by far the largest object of this kind ever seen. Material in the ball is at a temperature of 100 million degrees Celsius (for comparison the surface of the Sun is at 5500 degrees Celsius although material there is far denser than in the gas cloud).

It is distributed between the hundreds of galaxies in the cluster Abell 3266 at a distance of 250 million light years from the Sun. Dark matter, the exact nature of which is still poorly understood, holds both the cluster and the cloud of gas together.

As it moves through space, material is being stripped from the cloud by the gravity of galaxies in the cluster. Scientists estimate that gas equivalent to the mass of the Sun is stripped from the cloud every hour, forming a large tail with colder and denser clumps. Over time, material in the tail may go on to form new stars and galaxies within the cluster.