The Bullet Cluster is a cosmic collision site where two vast clouds of galaxies, gas, and invisible matter slammed into each other. When light from distant stars passes near such a cluster, gravity bends its path like a lens. Astronomers study these distortions to work out where the mass is hiding. Earlier maps were rough: precise distances to many of the galaxies seen in the distorted images were missing.
Now the James Webb Space Telescope has delivered sharp images and spectra. The team identified 135 reliable images from 27 distant galaxies with accurately measured distances. That allowed them to build a new model of the cluster. It turns out the main mass is elongated with two peaks, plus additional clumps nearby. The position of the brightest galaxy matches the center of mass to within 4,000 light-years — three times better than before.
The new map helps explain how the cluster grew and collided. It also provides a benchmark for testing theories about the nature of dark matter. When we look at such lenses, we are literally seeing the invisible.
The Bullet Cluster got its name from the bullet-shaped cloud of gas left behind after the collision of two clusters.