El Gordo: A Galaxy Cluster That Pushes the Limits

ACT-CL J0102-4915 (El Gordo)
Credit: X-ray: NASA/CXC/Rutgers/J. Hughes et al.;
Infrared: NASA/ESA/CSA, J.M. Diego (IFCA), B.Frye (Univ. of Arizona), P.Kamieneski, T.Carleton & R.Windhorst (ASU);

Image processing: X-ray: L. Frattare; J. Major, K.Arcand (SAO).

Infrared: A.Pagan (STScI), J.Summers (ASU), J.C.J.D'Silva (UWA), A.M.Koekemoer (STScI), A.Robotham (UWA), R.Windhorst (ASU)

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When astronomers discovered the galaxy cluster ACT-CL J0102-4915 in 2012 with NASA's Chandra X-ray Observatory and ground-based optical telescopes, they nicknamed it "El Gordo" (Spanish for the "Fat One") because of its gigantic mass. Scientists estimate that El Gordo contains as much as 3 million billion (3,000,000,000,000,000) times the mass of the Sun. Thanks to its heft, El Gordo acts as a natural lens, distorting the light from more distant objects behind it through a process known as gravitational lensing.

A new composite image of El Gordo shows the diffuse, superheated gas in the cluster observed in X-rays from Chandra (blue) that have been combined with a new infrared image from NASA's James Webb Space Telescope (red, green, and blue). Webb's image shows galaxies in El Gordo plus background galaxies located further away from Earth. El Gordo is located about 7.3 billion light-years from Earth and the background galaxies are at a range of different distances including several that are 12.3 billion light-years from Earth. The appearance of some of the background galaxies has been distorted into a variety of unusual and highly elongated shapes because of gravitational lensing by the cluster.

The X-ray image of El Gordo reveals a distinct cometary appearance. Along with optical data, astronomers reported in 2012 that this shape implies El Gordo is, in fact, the site of two galaxy clusters that ran into one another at several million miles per hour. The same study also used Chandra and other observatories to show that El Gordo is the most massive, and produces the most X-rays, of any known galaxy cluster at its distance or beyond.

Four new papers discussing the Webb observations have recently been accepted, including two that discuss Chandra data. Newer Chandra observations obtained after the 2012 study increase the exposure time by a factor of six, providing much more detailed information about the density and temperature of the cluster’s hot gas. Those Chandra-inclusive papers are led by Brenda Frye (University of Arizona) and Jose Diego (Instituto de Fisica de Cantabria, Spain). All four papers are part of the JWST “Prime Extragalactic Areas for Reionization and Lensing Science” (PEARLS) project led by Rogier Windhorst of Arizona State University. Highlights of the results from the papers are described in a press release from Space Telescope Science Institute.

NASA's Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.

Source: NASA’s Chandra X-ray Observatory

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Visual Description:

The primary image in today's release features a field of distant galaxies and stars with a bright blue, cone-shaped cloud at its core. The cloud is superheated gas in the galaxy cluster known as "El Gordo", meaning "Fat One" in Spanish. "El Gordo" is an immensely hefty galaxy cluster, with a mass as much as 3 million billion times the mass of the Sun.

In this composite image, the bright blue cloud has a cometary appearance, meaning it resembles a comet and its tail, with a bright tip that fades as the cone-shape widens. Here, the bright tip is positioned near our lower left, with the fading conical shape widening toward our upper right. In this image, the color blue represents X-ray light observed by Chandra. The properties of the gas cloud suggests a multi-million mile an hour collision of two galaxy clusters. This collision produces more X-rays than any other galaxy cluster observed at its distance or beyond.

Throughout the gas cloud, and in the background, are thousands of distant galaxies and stars, in whites, golden oranges, and blues. From this distance, some resemble simple specks of light. Others are slightly larger and feature refraction spikes, or upon close inspection, discernible spiraling arms. Many of the distant galaxies behind the cluster appear distorted or elongated. This visual distortion is due to El Gordo's great mass, which bends the light of these galaxies and distorts their appearance.

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Fast Facts for ACT J0102-4915 (El Gordo):

Scale: Image is about 2.3 arcmin (6 million light-years) across.
Category: Groups & Clusters of Galaxies
Coordinates (J2000): RA 01h 02m 52.50s | Dec -49° 14´ 58.00"
Constellation: Phoenix
Observation Dates: 3 pointings between 26 Jan 2011 and 21 Feb 2012
Observation Time: 97 hours 30 minutes (4 days 1 hour 30 minutes)
Obs. ID: 12258, 14022, 14023
Instrument: ACIS
Also Known As: ACT-CL J0102-4915

References: Frye, B. et al. 2023, ApJ, 952, 81 (preprint: arXiv:2303.03556); Diego, J. et al. 2023, A&A, 672, 3 (preprint: arXiv:2210.06514)

Color Code: X-ray: blue; Infrared: red, green, blue
Distance Estimate: About 7.3 billion light-years (z=0.87)

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NASA Hubble Team Finds Monster "El Gordo" Galaxy Cluster Bigger Than Thought

This is a Hubble image of the most massive cluster of galaxies ever seen to exist when the universe was just half its current age of 13.8 billion years. The cluster contains several hundred galaxies.  Image Credit: NASA, ESA, and J. Jee (University of California, Davis)

NASA's Hubble Space Telescope has weighed the largest known galaxy cluster in the distant universe, catalogued as ACT-CL J0102-4915, and found it definitely lives up to its nickname -- El Gordo (Spanish for "the fat one").

By measuring how much the cluster's gravity warps images of galaxies in the distant background, a team of astronomers has calculated the cluster's mass to be as much as 3 million billion times the mass of our sun. Hubble data show the galaxy cluster, which is 9.7 billion light-years away from Earth, is roughly 43 percent more massive than earlier estimates.

The team used Hubble to measure how strongly the mass of the cluster warped space. Hubble's high resolution allowed measurements of so-called "weak lensing," where the cluster's immense gravity subtly distorts space like a funhouse mirror and warps images of background galaxies. The greater the warping, the more mass is locked up in the cluster.

"What I did is basically look at the shapes of the background galaxies that are farther away than the cluster itself," explained lead author James Jee of the University of California at Davis. "It's given us an even stronger probability that this is really an amazing system very early in the universe."

A fraction of this mass is locked up in several hundred galaxies that inhabit the cluster and a larger fraction is in hot gas that fills the entire volume of the cluster. The rest is tied up in dark matter, an invisible form of matter that makes up the bulk of the mass of the universe.

Though equally massive galaxy clusters are found in the nearby part of the universe, such as the Bullet cluster, nothing like this has ever been discovered to exist so far back in time, when the universe was roughly half its current estimated age of 13.8 billion years. The team suspects such monster galaxy clusters are rare in the early universe, based on current cosmological models.

The immense size of El Gordo was first reported in January 2012. Astronomers estimated its mass based on observations made by NASA's Chandra X-ray Observatory, and galaxy velocities measured by the European Southern Observatory's Very Large Telescope array in Paranal, Chile. They were able to put together estimates of the cluster's mass based on the motions of the galaxies moving inside the cluster and the temperatures of the hot gas between those galaxies.

The challenge was that El Gordo looked as if it might have been the result of a titanic collision between a pair of galaxy clusters -- an event researchers describe as two cosmic cannonballs hitting each other.

"We wondered what happens when you catch a cluster in the midst of a major merger and how the merger process influences both the X-ray gas and the motion of the galaxies," explained John Hughes of Rutgers University. "So, the bottom line is because of the complicated merger state, it left some questions about the reliability of the mass estimates we were making."

That is where the Hubble data came in, according to Felipe Menanteau of the University of Illinois at Urbana-Champaign.

"We were in dire need for an independent and more robust mass estimate given how extreme this cluster is and how rare its existence is in the current cosmological model. There was all this kinematic energy that was unaccounted for and could potentially suggest that we were actually underestimating the mass," Menanteau said. 

The expectation of "unaccounted energy" comes from the fact the merger of galaxy clusters is occurring tangentially to the observers' line-of-sight. This means they are potentially missing a good fraction of the kinetic energy of the merger because their spectroscopic measurements only track the radial speeds of the galaxies.

The team's next step with Hubble will be to compile an image of the cluster. Because El Gordo does not fit into Hubble's field of view, the team will capture images of sections of the galaxy cluster and piece them together into a mosaic.

Researchers say it is like observing a giant from the side.

"We can tell it's a pretty big El Gordo, but we don't know what kind of legs he has, so we need to have a larger field of view to get the complete picture of the giant," said Menanteau.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Md., manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington.

For images and more information about Hubble, visit:  http://www.nasa.gov/hubble

J.D. Harrington
Headquarters, Washington
202-358-5241
j.d.harrington@nasa.gov

Ray Villard
Space Science Telescope Institute, Baltimore, Md.
410-338-4493 / 410-338-4514
villard@stsci.edu

Source: NASA's Hubble Space Telescope

El Gordo (ACT-CL J0102-4915): NASA's Chandra Finds Largest Galaxy Cluster in Early Universe

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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A composite image shows El Gordo in X-ray light from NASA's Chandra X-ray Observatory in blue, along with optical data from the European Southern Observatory's Very Large Telescope (VLT) in red, green, and blue, and infrared emission from the NASA's Spitzer Space Telescope in red and orange.

X-ray data from Chandra reveal a distinct cometary appearance of El Gordo, including two "tails" extending to the upper right of the image. Along with the VLT's optical data, this shows that El Gordo is, in fact, the site of two galaxy clusters running into one another at several million miles per hour. This and other characteristics make El Gordo akin to the well-known object called the Bullet Cluster, which is located almost 4 billion light years closer to Earth.

As with the Bullet Cluster, there is evidence that normal matter, mainly composed of hot, X-ray bright gas, has been wrenched apart from the dark matter in El Gordo. The hot gas in each cluster was slowed down by the collision, but the dark matter was not.

El Gordo is located over 7 billion light years from Earth, meaning that it is being observed at a young age. According to the scientists involved in this study, this cluster of galaxies is the most massive, the hottest, and gives off the most X-rays of any known cluster at this distance or beyond.

The central galaxy in the middle of El Gordo is unusually bright and has surprisingly blue colors in optical wavelengths. The authors speculate that this extreme galaxy resulted from a collision and merger between the two galaxies at the center of each cluster.

Using Spitzer data and optical imaging it is estimated that about 1% of the total mass of the cluster is in stars, while the rest is found in the hot gas that fills the space between the stars and is detected by Chandra. This ratio of stars to gas is similar with results from other massive clusters.

Fast Facts for El Gordo:

Scale Image is 5.3 arcmin across
Category: Groups & Clusters of Galaxies
Coordinates: (J2000) RA 01h 02m 52.50s | Dec -49° 14' 58.00"
Constellation: Phoenix
Observation Date: 01/26/2011
Observation Time: 16 hours 40 min.
Obs. ID: 12258
Color Code: X-ray (Blue); Optical (Red, Green, Blue); Infrared (Red)
Instrument: ACIS
Also Known As: ACT-CL J0102-4915
References: Menanteau, F. et al, 2011 ApJ (submitted); arXiv:1109.0953
Distance Estimate: 7.166 billion light years