Astronomy Notes

NASA finds direct proof of dark matter by observing this cosmic collision.

The pink clumps (hot gas) are detected by Chandra X-rays and contains most of the normal and baryonic matter in the two clusters.The bullet-shaped clump on the right is the hot gas from one cluster, which passed through the hot gas from the other larger cluster during the collision. The galaxies are shown in orange and white in optical image. What are the blue clumps? What has caused this scene?

This animation helps you to understand more about the collision. Download it here. (2.92MB)

Explanation by Chandra X-ray Observatory:

The blue areas in this image show where astronomers find most of the mass in the clusters. The concentration of mass is determined using the effect of so-called gravitational lensing, where light from the distant objects is distorted by intervening matter. Most of the matter in the clusters (blue) is clearly separated from the normal matter (pink), giving direct evidence that nearly all of the matter in the clusters is dark.

The hot gas in each cluster was slowed by a drag force, similar to air resistance, during the collision. In contrast, the dark matter was not slowed by the impact because it does not interact directly with itself or the gas except through gravity. Therefore, during the collision the dark matter clumps from the two clusters moved ahead of the hot gas, producing the separation of the dark and normal matter seen in the image. If hot gas was the most massive component in the clusters, as proposed by alternative theories of gravity, such an effect would not be seen. Instead, this result shows that dark matter is required.