NASA: “Massive Overdense Object” Observed at the Edge of the Known Universe” (Today’s Most Popular)




How did galaxy clusters evolve over time? What did they look like billions of years ago? To answer these questions, astronomers look back in time to our youthful universe. Because light takes time to reach us, we can see very distant objects as they were in the past. For example, we are seeing the newfound galaxy cluster — called Massive Overdense Object (MOO) J1142+1527 — as it existed 8.5 billion years ago, long before Earth formed.

This past November, astronomers discovered a giant gathering of galaxies in a very remote part of the universe, thanks to NASA's Spitzer Space Telescope and Wide-field Infrared Survey Explorer (WISE). The galaxy cluster, located 8.5 billion light-years away, is the most massive structure yet found at such great distances.


Galaxy clusters are gravitationally bound groups of thousands of galaxies, which themselves each contain hundreds of billions of stars. The clusters grow bigger and bigger over time as they acquire new members. As light from remote galaxies makes its way to us, it becomes stretched to longer, infrared wavelengths by the expansion of space.

For infrared space telescopes, picking out distant galaxies is like plucking ripe cherries from a cherry tree. In the infrared images produced by Spitzer, these distant galaxies stand out as red dots, while closer galaxies look white. Astronomers first combed through the WISE catalog to find candidates for clusters of distant galaxies. WISE catalogued hundreds of millions of objects in images taken over the entire sky from 2010 to 2011.

They then used Spitzer to narrow in on 200 of the most interesting objects, in a project named the "Massive and Distant Clusters of WISE Survey," or MaDCoWS. Spitzer doesn't observe the whole sky like WISE, but can see more detail.

"It's the combination of Spitzer and WISE that lets us go from a quarter billion objects down to the most massive galaxy clusters in the sky," said Anthony Gonzalez of the University of Florida in Gainesville, lead author of a new study published in the Oct. 20 issue of the Astrophysical Journal Letters.

From these observations, MOO J1142+1527 jumped out as one of the most extreme. The W.M. Keck Observatories and Gemini Observatory on Mauna Kea in Hawaii were used to measure the distance to the cluster at 8.5 billion light-years. Using data from the Combined Array for Research in Millimeter-wave Astronomy (CARMA) telescopes near Owens Valley in California, the scientists were then able to determine that the cluster's mass is a quadrillion times that of our sun — making it the most massive known cluster that far back in space and time.

MOO J1142+1527 may be one of only a handful of clusters of this heft in the early universe, according to the scientists' estimates.

"Based on our understanding of how galaxy clusters grow from the very beginning of our universe, this cluster should be one of the five most massive in existence at that time," said co-author Peter Eisenhardt, the project scientist for WISE at NASA's Jet Propulsion Laboratory in Pasadena, California.

In the coming year, the team plans to sift through more than 1,700 additional galaxy cluster candidates with Spitzer, looking for biggest of the bunch.

"Once we find the most massive clusters, we can start to investigate how galaxies evolved in these extreme environments," said Gonzalez.



An earlier discovery of a massive galaxy cluster took place in 2014 with the Chandra X-Ray Observatory. The Chandra study shows that the galaxy cluster, seen above at the comparatively young age of about 800 million years, is the most massive known cluster with that age or younger. As the largest gravitationally bound structures known, galaxy clusters can act as crucial gauges for how the universe itself has evolved over time.

The galaxy cluster was originally discovered using ESA’s XMM-Newton observatory and is located about 9.6 billion light-years from Earth. Astronomers used X-ray data from Chandra that, when combined with scientific models, provides an accurate weight of the cluster, which comes in at a whopping 400 trillion times the mass of the Sun. Scientists believe the cluster formed about 3.3 billion years after the Big Bang.

The cluster is officially named XDCP J0044.0-2033, but the researchers have nicknamed it “Gioiello,” which is Italian for “jewel.” They chose this name because an image of the cluster contains many sparkling colors from the hot, X-ray emitting gas and various star-forming galaxies within the cluster. Also, the research team met to discuss the Chandra data for the first time at Villa il Gioiello, a 15th century villa near the Observatory of Arcetri, which was the last residence of prominent Italian astronomer Galileo Galilei.

“Finding this enormous galaxy cluster at this early epoch means that there could be more out there,” said Paolo Tozzi of the National Institute for Astrophysics (INAF) in Florence, Italy. “This kind of information could have an impact on our understanding of how the large scale structure of the universe formed and evolved.”

Previously, astronomers had found an enormous galaxy cluster, known as “El Gordo,” at a distance of 7 billion light-years away and a few other large distant clusters. According to the best current model for how the universe evolved, there is a low chance of finding clusters as massive as the Gioiello Cluster and El Gordo. The new findings suggest that there might be problems with the theory, and are enticing astronomers to look for other distant and massive clusters.

“The hint that there might be problems with the standard model of cosmology is interesting,” said James Jee of the University of California in Davis, “but we need bigger and deeper samples of clusters before we can tell if there’s a real problem.”

The Chandra observation of the Gioiello Cluster lasted over four days and is the deepest X-ray observation yet made on a cluster beyond a distance of about 8 billion light-years.

“Unlike the galaxy clusters that are close to us, this cluster still has lots of stars forming within its galaxies,” said Joana Santos, also from INAF. “This gives us a unique window into what galaxy clusters are like when they are very young.”

In the past, astronomers have reported finding several galaxy cluster candidates that are located more than 9.5 billion light-years away. However, some of these objects turned out to be protoclusters, that is, precursors to fully developed galaxy clusters. Until, that is, the discovery of MOO J1142+1527.

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Image credits: NASA and NASA/CXC/INAF/P.Tozzi, et al; Optical: NAOJ/Subaru and ESO/VLT; Infrared: ESA/Herschel

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