The Space Infrared Telescope for Cosmology and Astrophysics (SPICA) is an international space observatory project mounted with the collaboration of researchers across the world to elucidate ďspace historyĀEfrom the Big Bang to the generation of life. By launching a large-scale telescope of 3.2m aperture and cooling it to cryogenic temperature of -267 deg. C, we will attempt to attain a level of extremely high-sensitivity observation never before realized. It is expected that SPICA observation will influence a wide range of fields from solar-system research to cosmology. R&D is underway toward the launch in FY2022.
Exploring the evolution of the universe with infrared observation
Infrared observation is indispensable to explore the evolution of the universe.
The primary role of infrared observation is to research the birth of stars and galaxies. It is believed that stars soon after birth (i.e. protostar) shine mainly in infrared. Fig. 1 shows a comparison of Orion observed in visible light and that observed in infrared by AKARI. The images indicate that the brilliantly shining areas are quite different when seen in invisible light and infrared. It is thought that the areas shining in infrared are just where stars are born.
Another role of infrared observation is to explore the younger universe. Our universe started with the Big Bang about 13.7 billion years ago and, after that, has continually expanded. Because of the effect of the expansion, when we see far-distant celestial bodies (i.e. bodies that existed in an earlier universe), their wavelengths become longer than original. In other words, while galaxies existing in the earlier universe originally shone in visible light, most of their energy observed by us has shifted to the infrared region. Thus, infrared observation is the most effective tool to explore the younger universe.
From AKARI to SPICA
Launched in 2006, AKARI has played an important role in infrared observation. One important result was its whole-sky survey observation by six wavelengths from 9 to 160 micro meters. Based on the observation, an infrared catalog recording 1.3 million celestial bodies was compiled. The majority of the bodies in the catalog are still unidentified, mysterious ones, however. In other words, they are a gold mine for future research.
When examining the nature of individual bodies, however, there is a limit in AKARIís capability. This is because the aperture of the telescope onboard AKARI is a mere 70 cm.
An important mission of SPICA is to advance our understanding of the evolution of the universe based on AKARIís results. To achieve this, SPICA needs ďhigh-spatial resolutionĀEand ďexcellent sensitivityĀEto exceed AKARI. Thus, we proposed installing a large-aperture telescope of 3.2m on SPICA, approximately five times the size of AKARIís. This should provide a large improvement in performance as shown in Fig. 2. With the map created by AKARI in one hand, we wish to set out on a treasure hunt.