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By NASA
X-ray: NASA/CXC/CfA/Stroe, A. et al.; Optical: PanSTARRS; Radio: ASTRON/LOFAR; Image Processing: NASA/CXC/SAO/N. Wolk New observations from NASA’s Chandra X-ray Observatory and other telescopes have captured a rare cosmic event: two galaxy clusters have collided and are now poised to head back for another swipe at each other.
Galaxy clusters are some of the largest structures in the Universe. Held together by gravity, they are monster-sized collections of hundreds or thousands of individual galaxies, massive amounts of superheated gas, and invisible dark matter.
The galaxy cluster PSZ2 G181.06+48.47 (PSZ2 G181 for short) is about 2.8 billion light-years from Earth. Previously, radio observations from the LOw Frequency ARray (LOFAR), an antenna network in the Netherlands, spotted parentheses-shaped structures on the outside of the system. In this new composite image, X-rays from Chandra (purple) and ESA’s XMM-Newton (blue) have been combined with LOFAR data (red) and an optical image from Pan-STARRs of the stars in the field of view.
These structures are probably shock fronts — similar to those created by jets that have broken the sound barrier — likely caused by disruption of gas from the initial collision about a billion years ago. Since the collision they have continued traveling outwards and are currently separated by about 11 million light-years, the largest separation of these kinds of structures that astronomers have ever seen.
Colliding galaxy clusters PSZ2 G181.06+48.47 (Labeled).X-ray: NASA/CXC/CfA/Stroe, A. et al.; Optical: PanSTARRS; Radio: ASTRON/LOFAR; Image Processing: NASA/CXC/SAO/N. Wolk Now, data from NASA’s Chandra and ESA’s XMM-Newton is providing evidence that PSZ2 G181 is poised for another collision. Having a first pass at ramming each other, the two clusters have slowed down and begun heading back toward a second crash.
Astronomers made a detailed study of the X-ray observations of this collision site and found three shock fronts. These are aligned with the axis of the collision, and the researchers think they are early signs of the second, oncoming crash.
The researchers are still trying to determine how much mass each of the colliding clusters contains. Regardless, the total mass of the system is less than others where galaxy clusters have collided. This makes PSZ2 G181 an unusual case of a lower-mass system involved in the rare event of colliding galaxy clusters.
A paper describing these results appears in a recent issue of The Astrophysical Journal (ApJ) and is led by Andra Stroe from the Center for Astrophysics | Harvard & Smithsonian (CfA) and collaborators. It is part of a series of three papers in ApJ. The second paper is led by Kamlesh Rajpurohit, also of CfA, and the third paper is led by Eunmo Ahn, from Yonsei University in the Republic of Korea.
NASA’s Marshall Space Flight Center in Huntsville, Alabama, 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.
Read more from NASA’s Chandra X-ray Observatory Learn more about the Chandra X-ray Observatory and its mission here:
https://www.nasa.gov/chandra
https://chandra.si.edu
Visual Description
In this release, a composite image illustrates a dramatic cosmic story unfolding 2.8 billion light years from Earth. Presented both with and without labels, the image details the fallout when two galaxy clusters collide.
At the center of the image are the colliding galaxy clusters, which together are known as PSZ2 G181. This combined cluster somewhat resembles an irregular violet peanut shell, with bulbous ends linked by a tapered middle. Inside each bulbous end are several glowing dots; some of the galaxies within the clusters. The violet peanut shape is tilted at a slight angle, surrounded by a blue haze of X-ray gas.
Far from the bulbous ends, at our upper left and lower right, are two blotchy, thick red lines. These are probably shock fronts, similar to those created by jets that have broken the sound barrier. Bracketing the combined galaxy cluster, these shock fronts were caused by the initial collision about a billion years ago. They are currently separated by 11 million light-years.
New data from the Chandra and XMM-Newton observatories suggests that PSZ2 G181 is poised for another powerful cosmic event. Having already taken one swipe at each other, the two clusters within are once again on a collision course.
News Media Contact
Megan Watzke
Chandra X-ray Center
Cambridge, Mass.
617-496-7998
mwatzke@cfa.harvard.edu
Lane Figueroa
Marshall Space Flight Center, Huntsville, Alabama
256-544-0034
lane.e.figueroa@nasa.gov
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Last Updated Jun 04, 2025 Related Terms
Chandra X-Ray Observatory Galaxies Galaxy clusters Marshall Astrophysics Marshall Space Flight Center The Universe
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X-ray: NASA/CXC/ICRAR, Curtin Univ./Z. Wang et al.; Infrared: NASA/JPL/CalTech/IPAC; Radio: SARAO/MeerKAT; Image processing: NASA/CXC/SAO/N. Wolk Scientists have discovered a star behaving like no other seen before, giving fresh clues about the origin of a new class of mysterious objects.
As described in our press release, a team of astronomers combined data from NASA’s Chandra X-ray Observatory and the SKA [Square Kilometer Array] Pathfinder (ASKAP) radio telescope on Wajarri Country in Australia to study the antics of the discovered object, known as ASKAP J1832−0911 (ASKAP J1832 for short).
ASKAP J1832 belongs to a class of objects called “long period radio transients” discovered in 2022 that vary in radio wave intensity in a regular way over tens of minutes. This is thousands of times longer than the length of the repeated variations seen in pulsars, which are rapidly spinning neutron stars that have repeated variations multiple times a second. ASKAP J1832 cycles in radio wave intensity every 44 minutes, placing it into this category of long period radio transients.
Using Chandra, the team discovered that ASKAP J1832 is also regularly varying in X-rays every 44 minutes. This is the first time that such an X-ray signal has been found in a long period radio transient.
In this composite image, X-rays from Chandra (blue) have been combined with infrared data from NASA’s Spitzer Space Telescope (cyan, light blue, teal and orange), and radio from LOFAR (red). An inset shows a more detailed view of the immediate area around this unusual object in X-ray and radio light.
A wide field image of ASKAP J1832 in X-ray, radio, and infrared light.X-ray: NASA/CXC/ICRAR, Curtin Univ./Z. Wang et al.; Infrared: NASA/JPL/CalTech/IPAC; Radio: SARAO/MeerKAT; Image processing: NASA/CXC/SAO/N. Wolk Using Chandra and the SKA Pathfinder, a team of astronomers found that ASKAP J1832 also dropped off in X-rays and radio waves dramatically over the course of six months. This combination of the 44-minute cycle in X-rays and radio waves in addition to the months-long changes is unlike anything astronomers have seen in the Milky Way galaxy.
A close-up image of ASKAP J1832 in X-ray and radio light.X-ray: NASA/CXC/ICRAR, Curtin Univ./Z. Wang et al.; Radio: SARAO/MeerKAT; Image processing: NASA/CXC/SAO/N. Wolk The research team argues that ASKAP J1832 is unlikely to be a pulsar or a neutron star pulling material from a companion star because its properties do not match the typical intensities of radio and X-ray signals of those objects. Some of ASKAP J1832’s properties could be explained by a neutron star with an extremely strong magnetic field, called a magnetar, with an age of more than half a million years. However, other features of ASKAP J1832 — such as its bright and variable radio emission — are difficult to explain for such a relatively old magnetar.
On the sky, ASKAP J1832 appears to lie within a supernova remnant, the remains of an exploded star, which often contain a neutron star formed by the supernova. However, the research team determined that the proximity is probably a coincidence and two are not associated with each other, encouraging them to consider the possibility that ASKAP J1832 does not contain a neutron star. They concluded that an isolated white dwarf does not explain the data but that a white dwarf star with a companion star might. However, it would require the strongest magnetic field ever known for a white dwarf in our galaxy.
A paper by Ziteng Wang (Curtin University in Australia) and collaborators describing these results appears in the journal Nature. Another team led by Di Li from Tsinghua University in China independently discovered this source using the DAocheng Radio Telescope and submitted their paper to the arXiv on the same day as the team led by Dr Wang. They did not report the X-ray behavior described here.
NASA’s Marshall Space Flight Center in Huntsville, Alabama, 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.
Read more from NASA’s Chandra X-ray Observatory Learn more about the Chandra X-ray Observatory and its mission here:
https://www.nasa.gov/chandra
https://chandra.si.edu
Visual Description:
This release features two composite images of a mysterious object, possibly an unusual neutron star or white dwarf, residing near the edge of a supernova remnant. The object, known as ASKAP J1832, has been intriguing astronomers from the Chandra X-ray Observatory and Square Kilometre Array Pathfinder radio telescope with its antics and bizarre behavior.
Astronomers have discovered that ASKAP J1832 cycles in radio wave intensity every 44 minutes. This is thousands of times longer than pulsars, which are rapidly spinning neutron stars that have repeated variations multiple times a second. Using Chandra, the team discovered that the object is also regularly varying in X-rays every 44 minutes. This is the first time such an X-ray signal has been found in a long period radio transient like ASKAP J1832.
In the primary composite image of this release, the curious object is shown in the context of the supernova remnant and nearby gas clouds. Radio data is red and and X-ray sources seen with Chandra are in dark blue. The supernova remnant is the large, wispy, red oval ring occupying the lower right of the image. The curious object sits inside this ring, to our right of center; a tiny purple speck in a sea of colorful specks. The gas cloud shows infrared data from NASA’s Spitzer Space Telescope and resembles a mottled green, teal blue, and golden orange cloud occupying our upper left half of the square image.
The second, close-up image shows a view of the immediate area around ASKAP J1832. In this composite image, infrared data from Spitzer has been removed, eliminating the mottled cloud and most of the colorful background specks. Here, near the inside edge of the hazy red ring, the curious object resembles a bright white dot with a hot pink outer edge, set against the blackness of space. Upon close inspection, the hot pink outer edge is revealed to have three faint spikes emanating from the surface.
The primary and close-up images are presented both unadorned, and with labels, including fine white circles identifying ASKAP J1832.
News Media Contact
Megan Watzke
Chandra X-ray Center
Cambridge, Mass.
617-496-7998
mwatzke@cfa.harvard.edu
Lane Figueroa
Marshall Space Flight Center, Huntsville, Alabama
256-544-0034
lane.e.figueroa@nasa.gov
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Last Updated May 28, 2025 EditorLee Mohon Related Terms
Chandra X-Ray Observatory Marshall Astrophysics Marshall Space Flight Center Neutron Stars Pulsars Stars The Universe
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