An interstellar pileup involving four galaxy clusters has
become the most crowded cluster collision ever detected.
Astronomers spotted the galaxy clusters involved in a triple
merger, the first time that such a phenomenon has been recorded. NASA's
Chandra X-Ray Observatory and Hubble Space Telescope joined the Keck
Observatory in Hawaii to safely observe the mess from 5.4 billion light years
away.
The cosmic
collision is taking place in MACSJ0717, a 13 million-light-year-long stream
of galaxies, gas and dark matter known as a filament. That filamentary freeway
continues to pour galaxies and other matter into a region already full of
galaxies.
"In addition to this enormous pileup, MACSJ0717 is also
remarkable because of its temperature," said Cheng-Jiun Ma, an astronomer
at the University of Hawaii. "Since each of these collisions releases
energy in the form of heat, MACS0717 has one of the highest temperatures ever
seen in such a system."
Collisions between galaxies can often result in larger
galaxies. Our Milky Way is slated for a run-in with a colossal
cloud of gas, and eventually will merge with the neighboring
Andromeda galaxy.
Researchers tracked the direction of the four clusters'
motions to figure out that the filament was the main culprit behind the galaxy
cluster collisions. The hottest region in MACSJ0717 is also where the filament
intersects the colliding clusters, which pointed to the high number of impacts.
Computer simulations show that the most massive galaxy
clusters should grow in regions where large-scale filaments of intergalactic
gas, galaxies, and dark matter intersect, and material falls inward along the
filaments.
"It's exciting that the data we get from MACSJ0717 appear to
beautifully match the scenario depicted in the simulations," Ma said.
Optical data
from Hubble and Keck provided information about galactic motion and density
along the telescopes' line of sight, while Chandra's X-ray data allowed the
researchers to fully determine the 3-D motion.
Ma and his team hope to use even deeper X-ray data to
measure the temperature of gas over the full 13 million-light-year extent of
the filament.
The study is fully detailed in the March 10 issue of the journal
Astrophysical Journal Letters.
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