For millennia, humans have been fascinated by the mysteries of the cosmos. From the Babylonians, to the Greeks, to the Egyptians and modern astronomers, the allure of the sky has inspired countless inquiries to uncover the secrets of the universe. Although cosmological models have existed for centuries, cosmology, which studies the evolution and structure of the universe, is relatively new. An innovative map of dark matter lays the groundwork for innovative models.
This science emerged in the early 20th century with Einstein‘s theory of general relativity, which serves as the basis for the standard model of cosmology. A series of papers submitted to the prestigious Astrophysical Journal by researchers at the Atacama Cosmology Telescope (ACT) have revealed a new image. This shows the map of dark matter distributed over a quarter of the entire sky, the most detailed ever created (ref.) (ref.) (ref.).
“We created a new map using the distortions of light left by the Big Bang” says Mathew Madhavacheril, lead author of one of the papers. “Surprisingly, it provides measurements that show both the ‘lumpiness’ of the universe and the rate at which it is growing after 14 billion years of evolution. These parameters are exactly what we expect from the standard model of cosmology based on Einstein’s theory of gravity”.
The quality of the lumpiness of the cosmos depends on the non-uniform distribution of dark matter. Its growth has remained consistent with previous predictions. Despite representing 85% of the universe and influencing its evolution, dark matter is difficult to detect because it does not interact with light or other forms of electromagnetic radiation. As far as we know, dark matter only interacts with gravity.
The light captured by the ACT has been used to produce a map of the cosmic microwave background radiation. This determines a new visualization of the distribution of dark matter in our sky.
The extraordinary ACT
The ACT was built by Penn and Princeton University. In 2007, it began observations to track dark matter. The over 160 collaborators who collected data observe the radiation emitted by the Big Bang. Cosmologists often refer to this diffuse radiation that fills our entire universe as the “baby picture of the cosmos”. Formally known as the Cosmic Microwave Background (CMB) radiation.
The team tracks how the gravitational attraction of large objects, including dark matter, distorts the CMB in its 14 billion year journey to us. It is like observing light being bent as it passes through a magnifying glass. “When we proposed this experiment in 2003, we had no idea of the scope of the information that could be extracted from our telescope” says Mark Devlin. “This was made possible by the intelligence of theorists, who built new tools to make our telescope more sensitive and by the new analysis techniques that our team devised”.
Penn researchers Gary Bernstein and Bhuvnesh Jain led the research on mapping dark matter using visible light emitted by nearby galaxies relative to the CMB light. “It is interesting to note that we found that matter is a bit less clumpy than the simplest theory predicts” says Jain. “However, the beautiful work of Mark and Mathew on the CMB perfectly agrees with theory. The extraordinary maps of dark matter from ACT narrow the search and reduce theoretical errors” says Bernstein.