Space and Physics
The Perseus cluster is enormous. It has a mass equivalent to 600 trillion Suns, and it looks like it has not stopped growing. New evidence suggests that it is undergoing a merging process with another cluster, and a bridge of dark matter has been the crucial clue to find this linked, but previously missed, companion.
Dark matter is a hypothetical and invisible substance that permeates the whole cosmos. It is invisible because it does not interact with light (or maybe it does so very weakly), so we can only infer its existence and presence through its gravitational interaction.
Using the Subaru/Hyper Suprime-Cam and archival data from the Sloan Digital Sky Survey, researchers have mapped the subtle alteration that the presence of this invisible matter would cause. It is known as weak gravitational lensing, and while it is a minute effect, it can be seen.
"This is the missing piece we’ve been looking for," Dr James Jee, corresponding author of the study, said in a statement. "All the odd shapes and swirling gas observed in the Perseus cluster now make sense within the context of a major merger."
There is some evidence that there has been a major interaction in this cluster. The fact that the hot gas is not symmetric and a peculiar distribution of galaxies were hints, but there was no certainty that a major collision was happening. However, the weak lensing provided the necessary evidence to work out the presence of a smaller cluster located 1.4 million light-years west of the main Perseus cluster, with a bridge of dark matter connecting the two. The companion has a mass of 200 trillion Suns.
"It took courage to challenge the prevailing consensus, but the simulation results from our collaborators and recent observations from the Euclid and XRISM space telescopes strongly support our findings," added Dr Hyeong Han Kim, the study’s first author.
"This breakthrough was made possible by combining deep imaging data from the Subaru Telescope with advanced gravitational lensing techniques we developed — demonstrating the power of lensing to unveil the hidden dynamics of the Universe’s most massive structures," said Jee.
The Perseus cluster is also well known for hosting a massive central galaxy, whose rotating black hole is responsible for producing the lowest note in the universe.
The study is published in the journal Nature Astronomy.
