Mysterious infrared light from space
A research team using the Atacama Large Millimeter/submillimeter Array (ALMA) has detected the faintest millimeter-wave source ever observed. By accumulating millimeter-waves from faint objects like this throughout the Universe, the team finally determined that such objects are 100% responsible for the enigmatic infrared background light filling the Universe. By comparing these to optical and infrared images, the team found that 60% of them are faint galaxies, whereas the rest have no corresponding objects in optical/infrared wavelengths and their nature is still unknown.
The Universe looks dark in the parts between stars and galaxies. However, astronomers have found that there is faint but uniform light, called the "cosmic background emission," coming from all directions. This background emission consists of three main components; Cosmic Optical Background (COB), Cosmic Microwave Background (CMB), and Cosmic Infrared Background (CIB).
The origins of the first two have already been revealed. The COB comes from a huge number of stars, and the CMB comes from hot gas just after the Big Bang. However, the origin of the CIB was still to be solved. Various research projects, including past ALMA observations, have been conducted, but they could only explain half of the CIB.
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