The Universe Revealed by Subaru Telescope Ⅶ
Cosmology is the study of the structure of the universe, its origin and formation. The research of extremely distant celestial objects using the Subaru Telescope makes important and continuing contributions to the observational cosmology.
Gravitational Lensing by Galaxy Clusters
Our view of a quasar that is located about 9.8 billion light years from Earth is being distorted by the gravitational lens effect of a massive cluster of galaxies that is about 300 trillion times more massive than our Sun and is located at some 6.2 billion light-years away. This is the first quasar to be observed through the gravitational lens of a galaxy cluster. Due to the lensing effect, one quasar appears as four different images around the cluster's center. The separation between the images is one of the largest such separations ever measured. This observation proves that a mysterious form of matter, called dark matter, must exist in this cluster of galaxies, and that its gravitational pull contributes to the lensing effect.
The Expansion of the Universe Detected Using Supernovae
The universe has been expanding since the Big Bang occurred about 14 billion years ago. The speed of the expansion is determined by the amount of matter and energy that the universe contains. By measuring the distance to a faraway object and the speed at which that object is receding from us, we can calculate the expansion rate of the universe. A type Ia supernova is a good "beacon" for this type of measurement because its maximum luminosity can be accurately determined. Subaru Telescope already has found more than 40 such supernovae that lie at least 7 billion light-years away. Such observational data will help astronomers verify with greater accuracy the acceleration of the expanding universe.
Distribution of Dark Matter
The distribution of dark matter, revealed by the gravitational lens effect. The length (height) indicates the direction of depth (the unit is redshift), and other indices show the spatial extent.
Throughout the universe, galaxies cluster together to form large-scale structure. In collaboration with the Hubble Space Telescope and others, the Subaru Telescope studied the gravitational lens effect caused by this large-scale structure. The Prime Focus Camera of Subaru Telescope was used to create multi-color images during the observation. The images obtained with Subaru have contributed to making an estimate of the distances to these galaxies. As a result, the distribution of dark matter has been described for the first time.