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Giant “ball of fire” hurtling through space

June 12, 2006
Courtesy European Space Agency
and World Science staff

Astronomers say they have found a comet-like “ball of fire,” over a billion times weightier than our Sun, plowing into a distant galaxy cluster.

By far the largest object of its kind ever identified, scientists say, it’s estimated to be moving at over 2.7 million kilometres (1.7 million miles) per hour. 

This X-ray image shows what astronomers say is a comet-like blob of gas about 5 million light-years long hurling through a distant galaxy cluster. The orange-red region represents the "comet." The head is at the lower left. The tail fans outward because there is less pressure to confine it. The red refers to regions of lower "entropy," a measure of disorder. The orange regions have higher entropy. This entropy map, different from brightness or temperature, helps scientists separate the cold and dense gas of the "comet" from the hotter and more rarefied gas of the cluster. The data show gas being stripped from the comet's core (entropy goes up) and forming a large tail containing lumps of colder and denser gas, astronomers say. The "comet" itself is a low-entropy gas; the ambient medium is a high entropy gas; the core of the comet has even lower entropy. The researchers estimate that a sun's worth of mass is lost every hour. (Credit: University of Maryland, Baltimore County)

The object is in a cluster of galaxies called Abell 3266, millions of light years from Earth, thus posing no danger to us, the researchers said. The cluster, one of the most massive such agglomerations in the southern sky, contains hundreds of galaxies and hot gas.

It’s also part of a “supercluster”—or cluster of galaxy clusters—called Horologium-Reticulum. 

Both cluster and supercluster are still growing, said Mark Henriksen, also of the University of Maryland, a member of the research team. The supercluster will become one of the largest mass concentrations in the nearby universe, he added; the fireball is a sign of that growth. 

“This is likely a massive building block being delivered to one of the largest assemblies of galaxies we know,” said Finoguenov.

The object appears from Earth as a circular glow of X-ray light with a comet-like tail nearly half the size of the moon, the astronomers said.

The gas ball is 46 million degrees C (83 million degrees F), Finoguenov added; the surrounding gas is even hotter, but emits fewer X-rays because it is sparser.

“What interests astronomers is not just the size of the gas ball but the role it plays in the formation and evolution of structure in the universe,” said Francesco Miniati of the Swiss Federal Institute of Technology in Zurich, Switzerland, another of the scientists. 

The group produced an “entropy map” of the gas ball, a technique that allows for separation of comet gas from the cluster gas based on temperature and density.

The map shows gas being stripped from the gas ball’s core and forming a large tail containing lumps of colder and denser gas, they said. This results in a comet-like formation. They added that about a sun’s worth of mass falls away each hour, not unlike the way dust sloughs off a comet’s tail. 

The fireball wouldn’t actually related to comets in any way, other than in its general form. Comets are balls of dust and ices that are tiny compared to the reported fireball.

With the fireball, “We are seeing structure formation in action,” said Henriksen. The cluster’s hot gas is “stripping off and dispersing gas that perhaps one day will seed star and galaxy growth within the cluster.”

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