Webb Telescope Reveals New Details of Bullet Cluster
JWST provides unprecedented views of dark matter distribution.
Nearly four billion light-years distant, the Bullet Cluster, a cosmic crash site of two massive galaxy clusters, has been studied in greater detail than ever before thanks to the James Webb Space Telescope. These observations refine the cluster’s mass and dark matter distribution.
Mapping the Invisible: Dark Matter’s Role
By observing the Bullet Cluster with Webb’s infrared capabilities, astronomers are refining measurements of its mass. The cluster is composed of two sub-clusters, with the smaller having collided with the larger one in the distant past. High-resolution images reveal faint galaxies beyond the cluster and map the distribution of hot gas, crucial to understanding dark matter. According to Sangjun Cha, lead author of a paper in The Astrophysical Journal Letters, “With Webb’s observations, we carefully measured the mass of the Bullet Cluster with the largest lensing dataset to date, from the galaxy clusters’ cores all the way out to their outskirts.”
Dark matter’s influence extends to the light from distant galaxies passing through the cluster. Kyle Finner, assistant scientist at IPAC at Caltech, notes, “Webb’s images dramatically improve what we can measure in this scene — including pinpointing the position of invisible particles known as dark matter.”
Cosmic Collision Unveiled
The Bullet Cluster’s name originates from the bow shock created as the smaller cluster plowed through the larger one, heating gas to millions of degrees. Chandra X-ray observations have pinpointed these hot gas clouds.
The separation of hot gas and dark matter during the collision offers critical evidence supporting the existence of dark matter. The hot gas slowed due to ram pressure, while the dark matter passed through unimpeded. Finner explains, “As the galaxy clusters collided, their gas was dragged out and left behind, which the X-rays confirm.”
Data from Webb indicates dark matter aligns with the galaxies, unaffected by the collision. As of 2023, dark matter is estimated to constitute 85% of the universe’s mass (NASA).
Gravitational Lensing: A Cosmic Magnifying Glass
Dark matter bends light around the Bullet Cluster, acting as a gravitational lens. This phenomenon magnifies and distorts light from distant galaxies, allowing astronomers to study objects otherwise too faint to observe. According to James Jee, professor at Yonsei University and research associate at UC Davis, “Gravitational lensing allows us to infer the distribution of dark matter.”
The distortion of these background galaxies maps the distribution of dark matter within the lens.
These observations suggest that dark matter particles interact primarily through gravity, placing tighter constraints on their behavior. The distribution of dark matter in the cluster reveals that its particles act independently, challenging scientists to determine their fundamental nature.
Further Exploration
NASA Webb ‘Pierces’ Bullet Cluster, Refines Its Mass
A High-Caliber View of the Bullet Cluster through JWST Strong and Weak Lensing Analyses
