You are looking at the most precise gravity map ever made of a distant galaxy cluster. Using the map, astronomers have determined that the cluster is roughly 650,000 light-years across and contains enough matter to make 160 trillion suns.
Image: ESA/Hubble, NASA, HST Frontier Fields Acknowledgement: Mathilde Jauzac (Durham University, UK and Astrophysics & Cosmology Research Unit, South Africa) and Jean-Paul Kneib (École Polytechnique Fédérale de Lausanne, Switzerland)
The cluster, known as MCS J0416.1–2403, is located about 4 billion light-years away and consists of hundreds of galaxies all orbiting one another. Newton’s gravitational equations can tell you the mass of two objects orbiting one another, provided you already know the mass of one of them. However, because these galaxies are all so distant, there is no way for scientists to determine any of their individual masses.
But there is another way. Einstein’s theory of general relativity tells us that heavy objects warp the fabric of space-time around them. As light travels through these warped regions it will become distorted, and we see that as smeared out rings and arcs in our telescopes, an effect known as gravitational lensing. Using the Hubble space telescope, astronomers identified smudges in the light seen around MCS J0416.1–2403. These distortions are images of even more distant galaxies sitting behind the cluster; their light has been lensed by its enormous mass. By carefully determining just how much the light is smeared out, researchers can calculate the amount of matter sitting within the galaxy cluster.
The 160 trillion solar masses includes both visible matter and dark matter, which gives off no light but makes up the bulk of the cluster’s mass. By studying the dynamics of all the galaxies within the cluster, astronomers can better understand this mysterious substance. Researchers will also continue mapping the smeared out images to increase the precision of their mass calculations, learning about the cluster’s finer details to figure out its history and evolution.