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The Forefront of Space Science

The Night Sky Is Bright!? - About the Mysteries of the Near-infrared Background Radiation -
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The Key to Deciphering the History of Universe: Cosmic Background Radiation

As we all know, the night sky is dark. However, the astronomer Olbers in the 19th century had questions on this fact. Why is the night sky dark? If the universe is infinite and static, we must see stellar surface everywhere in the sky, so the night sky should be completely bright like the surface of the sun. This is the well-known “Olbers' paradoxE As you know, this paradox is solved, since the universe is finite.

It is true that the night sky is dark. In fact, however, it is not totally dark. There are weak radiations shining across the sky called the “Cosmic Background RadiationE What is the Cosmic Background Radiation shining in the sky? Actually, the Cosmic Background Radiation is the aggregation of the history of universe from the beginning to now. To say it in another word, with the researches on the Cosmic Background Radiation, we can decipher the history of universe.

The Cosmic Microwave Background Radiation, which is one of the traces of the Big Bang, is especially famous (For details, please check the article by Dr. Tomotake Matsumura in the ISAS News August 2015 Issue (No.413)). However, the universe is filled not only with the microwaves, but also with radio waves, infrared lights, visible lights, X-rays and gamma rays. If we can reveal the origin of the Cosmic Background Radiation, we will be able to understand the entire history of the universe. For example, we can look back at the history of the stars and the galaxies, which are the basic components of the universe, from the visible and infrared lights, as well as the formation history of black holes from the X-rays.

In the ISAS News February 2005 Issue (No.287), Prof. Toshio Matsumoto (professor emeritus of JAXA, now works at the Academia Sinica, Taiwan) wrote an article called “The Night Sky is Bright!? - Exploring the First Light in the Universe -E In this article, focusing on the near infrared (0.75~1.4μm) near the visible lights which we can see every day, we will introduce the progress and discussions, together with our researches, on the Cosmic Near-infrared Background during the 10 years after Prof. Matsumoto’s article. You will be interested in the progress of science if you read this article together with Prof. Matsumoto’s article. (*1)

(*1):So far, there have been many articles on the Cosmic Background Radiation in ISAS News. Such as the article on the microwave field by Dr. Tomotake Matsumura, the article on the far infrared ray field by Prof. Shuji Matsuura and the article on the X-ray field by Prof. Yoshihiro Ueda. Although there has not been any article on the gamma ray field, I wrote an article in the Butsuri (Journal of the Physical Society of Japan) and I hope you can read it. It is a fact worthy of special mention that Japan’s space science researches have made great contributions to the researches on the Cosmic Background Radiation.

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