The Universe Revealed by Subaru Telescope Ⅳ

The Realm of the World of Galaxy

A galaxy is a large group of stars and the universe is populated by galaxies. They can be arranged in many diverse shapes and sizes. The question "What creates this diversity?" is one that many scientists are trying to answer. Studying the dynamics of galaxy collisions and mergers is key to understanding the formation of the galaxies we study today.


In order to obtain an overall image of the spiral galaxy NGC2403, a camera with a wide field of view is needed. Subaru Prime Focus Camera captured this image of this galactic neighbor, which lies relatively close to us (about 10 million light-years away). NGC2403 is a Sc-type galaxy, which means that its spiral shape is relatively loose. Its mass is about the half that of the Milky Way, and it contains a lot of neutral hydrogen gas. Areas of interest include a red-colored region of its spiral arms where star creation is actively occurring, a group of young blue stars, and a dark area where starlight is hidden by dust. Such regions indicate that numerous stars are being born within this galaxy.

Massive Gas Cloud Surrounding Active Galaxy

An ionized hydrogen gas cloud 110,000 light years across was discovered surrounding galaxy NGC4388 (60 million light-years away). It appears in this image as a series of purple-red clouds spreading toward the upper left from the galactic center. This active galaxy is harboring a million-solar-mass black hole at its heart. When matter falls into this massive black hole it emits strong radiation, which lights up surrounding clouds. The gas clouds may form as a result of interactions between NGC4388 and high-temperature gas surrounding the galaxy, or by interactions between NGC4388 and smaller galaxies nearby.

Cluster of Galaxies

Galaxies are often found crowded together in groups and clusters. The image above is the central part of a large galaxy cluster as it appears about 7 billion years ago, when the universe was about half as old as it is today. The scale is such that one side of the picture covers about 4.5 million light-years, which is about twice the distance from our Milky Way Galaxy to neighboring Andromeda. Hundreds of galaxies are crowded into this small space. In this image, the reddish galaxies appear to form a chain from the top left to the bottom right, indicating that the galaxies are in the process of evolving into even larger clusters due to the pull of each other's gravity. The blue galaxies exist farther away, so when their light passes by the cluster it is bent and stretched by the gravitational lens created by the galaxy cluster.

Commentary from Dr. Kouji Ohta, Associate Professor at Kyoto University :

Imaging capability for viewing detailed structures in a wide field of view is one of the strong points of the Subaru Telescope. Subaru is also capable of spectroscopic observations of many objects simultaneously. Using this wide field of view, astronomers can image the extended structure of galaxies ranging from those near us to galaxies billions of light years away. Observations in other wavelengths, such as in the millimeter and the sub-millimeter region, using the Atacama Large Millimeter/submillimeter Array (ALMA) will greatly help astronomers understand the evolution of galaxies.

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