Galactic Cluster Clash Spotted in Early Universe


Say hello to “El Gordo,” one of the biggest cosmic collisions you will ever witness.

Radiating brightly in X-ray and infrared emissions, El Gordo — meaning “the big one” or “the fat one” in Spanish, a nickname given to the object by astronomers — is two galactic clusters smashing into one another 7 billion light-years away.

However, the term “smashing into one another” isn’t entirely accurate. Indeed, the two clusters of galaxies are going through a head-on collision, and they are ploughing through space at a breakneck speed of several millions of miles per hour, but few (if any) of the stars contained within the galaxies inside the clusters will physically collide.

ANALYSIS: Where is Dark Matter Hiding?

There is a lot of space between the galaxies and stars, so they’ll simply whiz past one another — but the gravitational turmoil caused by these two clusters colliding is fierce and interactions between the shocked gas and dust are dazzlingly beautiful.

“This cluster is the most massive, the hottest, and gives off the most X-rays of any known cluster at this distance or beyond,” said Felipe Menanteau of Rutgers University in New Brunswick, N.J., who led the study.

But there’s also an invisible battle unfolding inside this cosmic Clash of the Titans: vast clouds of dark matter — the stuff that makes up over 80 percent of the entire mass of the universe — are blasting through the colliding clusters resembling a cloud of angry bees swarming around a hive.

NEWS: Vast Web of Dark Matter Mapped

Though the dark matter particles do not interact with normal matter (they cut through all the clouds of gas and dust seen in this image as if they didn’t exist), the gravitational effects of dark matter on normal matter can be studied. And it is huge colliding clusters like El Gordo that are so valuable to astronomers.

“Gigantic galaxy clusters like this are just what we were aiming to find,” said team member Jack Hughes, also from Rutgers University. “We want to see if we can understand how these extreme objects form using the best models of cosmology that are currently available.”

The discovery of this colliding cluster 7 billion light-years away is the furthest known example. As it took 7 billion years for its light to travel to Earth, the collision actually happened when the Universe was only half the age it is now (13.75 billion years old). The famous “Bullet Cluster,” another pair of colliding clusters used by astronomers to study dark matter, is located much closer — at 4 billion light-years distant.

ANALYSIS: Dark Matter Found in Colliding Galaxies

“This is the first time we’ve found a system like the Bullet Cluster at such a large distance,” said Cristobal Sifon of Pontificia Universidad de Catolica de Chile (PUC) in Santiago. “It’s like the expression says: if you want to understand where you’re going, you have to know where you’ve been.”

By combining observations by NASA’s Chandra X-Ray Observatory, the European Southern Observatory’s Very Large Telescope (VLT) in Chile and NASA’s Spitzer Space Telescope, the X-ray, optical and infrared radiation being produced by El Gordo can be seen. The X-ray emissions being observed by Chandra is produced by normal matter being wrenched from the accompanying dark matter during the collision — superheated gases collide and slow down (producing X-rays), whereas dark matter zips straight through the mess.

The extraordinary discovery of El Gordo was presented at the American Astronomical Society meeting at Austin, Texas on Tuesday.

Image credit: X-ray: NASA/CXC/Rutgers/J.Hughes et al, Optical: ESO/VLT/Pontificia Universidad. Catolica de Chile/L.Infante & SOAR (MSU/NOAO/UNC/CNPq-Brazil)/Rutgers/F.Menanteau, IR: NASA/JPL/Rutgers/F.Menanteau

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