BULLET THROUGH THE HEART Chandra captured the heat from gas (pink) associated with two galaxy clusters that have crashed together and passed through each other in what's known as the Bullet Cluster (1E 0657-56). The bullet shape of the gas clump at right comes from its passage through the gas clump at left. The mass of the clusters, as measured by the effect of their gravity on distant galaxies in the background, is marked in blue. Galaxies appear in orange and white. The majority of the mass is not associated with the hot gas, as proposed by alternate theories of gravity; most of the mass of these clusters is thus unseen. COLLISION The four artist's illustrations at top demonstrate the collision that created the Bullet Cluster; the final panel mimics the actual data shown in the X-ray image. Hot gas is red and dark matter blue. As the hot gas associated with each of the two clusters collided, a drag force slowed and reshaped it. However, the dark matter passed through unimpeded. sk yand tele scope .o r g * JULY 2024 15 COLLISION CONCEPT: NASA / CXC / M. WEISS; BULLET CLUSTER: X-RAY: NASA / CXC / CFA / M. MARKEVITCH ET AL.; OPTICAL: NASA / STSCI; MAGELLAN / U. ARIZONA / D. CLOWE ET AL.; LENSING MAP: NASA / STSCI / ESO WFI / MAGELLAN / U. ARIZONA / D. CLOWE ET AL.http://skyandtelescope.org