In the latest stunning visual feat by NASA’s James Webb Space Telescope, the American space agency’s premiere space observatory has delivered high-resolution images of what astronomers call the Bullet Cluster, revealing its complex dynamics.
The new images, made possible using Webb’s near-infrared capabilities, reveal a cosmic collision between two galaxy clusters, allowing researchers to map them more completely than previously achieved.
Located within the Carina constellation 3.8 billion light-years from Earth, the Bullet Cluster as seen in the recent Webb imagery is also providing researchers with a new means of exploring one of the most enduring mysteries of the cosmos: the distribution of mysterious dark matter throughout the universe.
A Means of Mapping Dark Matter
Along with the stars and other stellar material that make up galaxies in our universe, astrophysicists also believe they contain dark matter, a mysterious nonluminous material that is theorized to take one of several potential forms.
In the case of the Bullet Cluster, a pair of very massive galactic clusters comprise this massive celestial formation, the two of them bound together by their gravitational influence on each other. A unique aspect of this gravitational concentration is that these clusters function as gravitational lenses, which offer an enhanced view of light emanating from more distant galaxies behind them.
James Jee, a professor at Yonsei University, research associate at UC Davis in California, and co-author of a new research paper on the Bullet Cluster based on Webb’s recent imagery, says that the colliding cluster’s gravitational lensing also helps researchers like him infer the distribution of dark matter in distant regions of space.
Fundamentally, the new Webb observations allowed Lee and his colleagues to measure the mass of the Bullet Cluster using the largest dataset based on gravitational lensing yet collected.
Kyle Finner, a co-author and an assistant scientist at IPAC at Caltech in Pasadena, California, said the images “dramatically improve what we can measure in this scene — including pinpointing the position of invisible particles known as dark matter.”
Thousands of Galaxies Measured
In their study, the team measured thousands of galaxies, which allowed them to obtain precision measurements of both visible and invisible mass contained within the Bullet Cluster, mapping light from nearby intracluster stars which have escaped the bounds of any specific galaxies.
“We confirmed that the intracluster light can be a reliable tracer of dark matter, even in a highly dynamic environment like the Bullet Cluster,” said Sangjun Cha, a PhD student at Yonsei University in Seoul, South Korea, and the new study’s lead author. According to Cha, these instracluster stars may be gravitationally bound to dark matter rather than any galaxies, a finding that could prove to be extremely beneficial for researchers studying our universe’s nonluminous matter and its characteristics.
Since dark matter’s non-luminosity effectively makes it invisible to observations by astronomers, the team was able to discern that it shows no signs of significant self-interaction. This was a crucial finding for the team, since any signs of self-interaction would have likely been revealed in the new Webb imagery as an offset between galaxies and the dark matter they are believed to be associated with.
Finner said that the collisions between these galaxies was validated in part through the detection of X-rays.
“As the galaxy clusters collided, their gas was dragged out and left behind, which the X-rays confirm,” Finner said, which he says shows that dark matter was similarly preserved instead of being dragged away, meaning that it must still align with the current position of the galaxies.
Galaxies in Collision
The new observations provide astronomers with stronger limits on the behavior of dark matter particles than any previous measurements, while lending further verification of the presence of this invisible mass that was collected during past observations.
An additional observation the team made involves unusual clumps and elongated mass they identified, which suggests that the Bullet Cluster may have formed through multiple galaxy cluster collisions billions of years ago.
Going forward, researchers will gain expansive near-infrared imagery from NASA’s Nancy Grace Roman Space Telescope, scheduled for launch by May 2027.
“With Roman, we will have complete mass estimates of the entire Bullet Cluster, which would allow us to recreate the actual collision on computers,” Finner says.
The team’s new research paper, “A High-Caliber View of the Bullet Cluster through JWST Strong and Weak Lensing Analyses,” was published in The Astrophysical Journal Letters on June 30, 2025.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. He can be reached by email at micah@thedebrief.org. Follow his work at micahhanks.com and on X: @MicahHanks.