Massive Galaxy Cluster: 1000 x Size of Milky Way

European Space Agency’s orbiting X-ray observatory XMM-Newton provided astronomers a glimpse of the largest cluster of galaxies ever seen in the distant, early universe. The discovery of this far-off group, estimated to contain a thousand times the mass of our own galaxy, the Milky Way,offers further proof of the existence of enigmatic dark energy.





“This is the most luminous, and therefore probably the most massive, cluster of galaxies discovered at this epoch,” said Georg Lamer of the Astrophysikalisches Institut Potsdam in Germany, who led the team. “The light we observe started about 7.7 billion years ago. This is about half of the age of the universe, so it is from quite long ago, and quite far away.” 

A team of astronomers discovered the record-breaking cluster as they were performing a systematic analysis of a catalog of 3500 observations performed with XMM-Newton’s European Photon Imaging Camera (EPIC) covering about 1% of the entire sky.  The catalog contains more than 190,000 individual X-ray sources.

The team was looking for extended patches of X-rays that could either be nearby galaxies or distant clusters of galaxies.  

“The very presence of this cluster confirms the existence of a mysterious component of the Universe called dark energy.” J083026+524133, as it’s known, stood out because it was so bright. While checking visual images from the Sloan Digital Sky Survey, the team could not find any obvious nearby galaxy in that location. So they turned to the Large Binocular Telescope in Arizona and took a deep exposure, finding cluster of galaxies. So the team calculated a distance of 7.7 thousand million light-years and the cluster’s mass using the XMM-Newton data. This was not a surprise because XMM-Newton is sensitive enough to routinely find galaxy clusters at this distance.

“Such massive galaxy clusters are thought to be rare objects in the distant Universe. They can be used to test cosmological theories,” says Lamer. Indeed, the very presence of this cluster confirms the existence of a mysterious component of the Universe called dark energy.

No one knows what dark energy is, but it is causing the expansion of the Universe to accelerate. This hampers the growth of massive galaxy clusters in more recent times, indicating that they must have formed earlier in the Universe. “The existence of the cluster can only be explained with dark energy,” says Lamer.

Yet he does not expect to find more of them in the XMM-Newton catalog. “According to the current cosmological theories, we should only expect to find this one cluster in the 1% of sky that we have searched,” says Lamer.

Posted by Casey Kazan.



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