How were astronomers able to map the dark matter in the Bullet Cluster? By seeing the distribution of galaxies in the Bullet Cluster after the collision of two clusters By observing X-rays emitted from the gas cloud in the Bullet Cluster By receiving radio signals from the Bullet Cluster using a radio telescope By seeing the subtle distortion of light from further. away galaxies as it passed through the Bullet Cluster

The correct answer is **By seeing the subtle distortion of light from further-away galaxies as it passed through the Bullet Cluster.**<br /><br />This technique is called gravitational lensing. While dark matter doesn't emit or absorb light, it does have mass, and therefore gravity. This gravity warps the fabric of spacetime around it. When light from distant galaxies passes through this warped spacetime near the Bullet Cluster, its path is slightly bent. By carefully mapping these distortions, astronomers can infer the distribution of mass, including the dark matter, within the cluster.<br /><br />The collision of two galaxy clusters in the Bullet Cluster provided a unique opportunity to study dark matter. The visible matter (mostly hot gas) interacted and slowed down during the collision, detected via X-ray observations. However, the gravitational lensing maps showed that the majority of the mass (the dark matter) passed right through each other without interacting much, just as expected for dark matter. This provided strong evidence for the existence and properties of dark matter.<br />