A new record for the most distant galaxy cluster has been set using NASA’s Chandra X-ray Observatory and other telescopes. This galaxy cluster may have been caught in a brief, but important stage of evolution never seen before.

The galaxy cluster is called CL J1001+0220 (CL J1001 for short) and is located about 11.1 billion light years from Earth. The discovery of this object pushes the formation time of galaxy clusters – the largest structures in the Universe held together by gravity – back by about 700 million years. 

 “This galaxy cluster isn’t just remarkable for its distance, it’s also going through an amazing growth spurt unlike any we’ve ever seen,” says Tao Wang of The French Alternative Energies and Atomic Energy Commission (CEA) in France, who led the study.  

Nine massive galaxies in a baby boom of stars

The core of CL J1001 contains altogether eleven massive galaxies – nine of which are experiencing an impressive baby boom of stars.

More specifically, stars are forming in the cluster’s core at a rate that is equivalent to over 3,000 Suns forming per year, a remarkably high value for a galaxy cluster, including those that are almost as young and distant as CL J1001.

The diffuse X-ray emission detected by Chandra and ESA’s XMM-Newton Observatory comes from a large amount of hot gas, one of the defining features of a true galaxy cluster. 

“It appears that we have captured this galaxy cluster at a critical stage just as it has shifted from a loose collection of galaxies into a young, but fully formed galaxy cluster,” says co-author David Elbaz, also of CEA. 

Violent outbursts of elliptical galaxies inside a cluster

The results suggest that elliptical galaxies in galaxy clusters like CL J1001 may form their stars during shorter and more violent outbursts than elliptical galaxies that are outside clusters. Also, this discovery indicates that much of the star formation in these galaxies happens after the galaxies fall onto the cluster, not before.

In comparing their results to computer simulations performed by other scientists of the formation of clusters, the team of astronomers reporting now found that CL J1001 has an unexpectedly high amount of mass in stars compared to the cluster’s total mass.

This may show that the build-up of stars is more rapid in distant clusters than simulations imply, or it may show that clusters like CL J1001 are so rare that they are not found in today’s largest cosmological simulations.

“We think we’re going to learn a lot about the formation of clusters and the galaxies they contain by studying this object,” says co-author Alexis Finoguenov, from University of Helsinki, “and we’re going to be searching hard for other examples.”

With Chandra the only limitation is the formation of clusters

Deep X-ray data which were recently accumulated by Chandra, has opened a door to an unprecedented cluster search.

“Our sensitivity allows a detection of such clusters at any redshift, and we are only limited by the formation of clusters. The current example is a very good illustration of this capability," Finoguenov explains.

The result presented now is based on data from a large group of observatories in space and on the ground including Chandra, NASA’s Hubble Space Telescope and Spitzer Space Telescope, XMM-Newton and Herschel Space Observatory, the NSF’s Karl G. Jansky Very Large Array, the ALMA Observatory, the IRAM Plateau de Bure Interferometer and the Very Large Telescope.

The paper describing these results will appear in The Astrophysical Journal and is available online (https://arxiv.org/abs/1604.07404).

NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.

Read more on the future of astronomy exploring new uncharted territory by Professor Alexis Finoguenov from the Department of Physics at the University of Helsinki.

For more: Alexis Finoguenov, alexis.finoguenov@helsinki.fi, tel. 02941 40997