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In the letter: MIT astronomers have discovered previously unidentified galaxy clusters that had been overlooked by previous studies. Their results, which were recently published in The Astrophysical Journal, suggest that up to one percent of galaxy clusters could be mistakenly identified as a single bright galaxy.
Clusters of galaxies containing hundreds or even thousands of individual galaxies are held together by gravity. As MIT points out, they travel through a sea of hot gases called an intracluster medium, and emit x-rays that we can see using space telescopes.
This radiation creates a “hazy halo” around clusters of galaxies, making them easier to identify from an object with a single x-ray source, such as a star or a quasar.
As MIT Associate Professor Michael McDonald discovered in 2012, however, not all clusters adhere to this general principle. The cluster he discovered, dubbed the Phoenix cluster, contains a black hole that emits x-rays bright enough to drown out radiation from the intracluster medium. So, it looked like a single x-ray source and was misclassified for decades.
Armed with this new possibility, the Clusters Hiding in Plain Sight (CHiPS) survey was born. During its six-year period, the investigation identified three new galaxy clusters, one of which is similar to the Phoenix cluster. This is remarkable considering that astronomers are only familiar with a few Phoenix-style bands.
McDonald’s hopes the results of the CHiPS survey will help others, such as those who work with the eROSITA X-ray instrument, to better understand how to search for clusters.
“The people who are building the cluster research for this new x-ray telescope need to be aware of this work,” McDonald said. “If you miss one percent of the clusters, there is a fundamental limit to your understanding of the universe.”
Courtesy meeting images
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