A mirror of "KAGRA" which could observe the "Gravity wave" was ready for use

Recently the NHK News On-line reported the following:

「重力波」を観測する「ＫＡＧＲＡ」の鏡が完成

2018年8月21日 15時47分

東京大学などが岐阜県で建設を進める宇宙から伝わる「重力波」を観測する施設、「ＫＡＧＲＡ」の心臓部の１つとなる鏡が完成し、21日披露されました。「ＫＡＧＲＡ」は来年、本格的な観測を開始する計画です。

「ＫＡＧＲＡ」用の鏡は東京大学と日本のメーカーなどが４つ製作し、その１つが21日、東京大学で披露されました。

直径は22センチ、厚さは15センチあり、素材は「サファイア」でできています。

重力波を観測する「ＫＡＧＲＡ」は東京大学などが岐阜県飛騨市の地下に建設を進めている大型の施設で、Ｌ字に組み合わせた長さ３キロメートルある２本のパイプの中を、両端の鏡で反射させたレーザーの光が往復する仕組みです。

宇宙から重力波が伝わってくると３キロのパイプがわずかにひずみ、中を走るレーザー光の往復時間が微妙に変化することから、重力波を検知することができます。

重力波は、水素原子よりも小さい空間の伸び縮みの変化として伝わってくるため、レーザーを反射する鏡には極めて高い精度が求められます。ＫＡＧＲＡでは、氷点下およそ250度に鏡を冷やすことで、誤差やノイズの発生を極限まで抑える世界初の技術を採用したということです。東京大学などでは今後、鏡を取り付けて、来年、本格的な観測を開始する計画です。

東京大学宇宙線研究所の廣瀬榮一特任助教は「鏡がついに完成し、これから重力波を観測するモードに入る。人類が知らない宇宙の謎を追いかけたい」と話しています。

重力波とは超新星爆発や天体どうしの衝突などで、時空に「ゆがみ」が発生してそれが波のように伝わる現象で、アインシュタインが存在を予想し、これまでにアメリカとヨーロッパの施設が観測に成功しています。宇宙の成り立ちの謎の解明にもつながるとされ、今後、ＫＡＧＲＡの成果が期待されます。

Translation

It was announced on the 21^st that a piece of mirror which was the key part of "KAGRA" was completed. “KAGRA” was the facility which could observe the "Gravity wave" transmitted from the universe; its construction was being advanced by the University of Tokyo and others in Gifu-ken. "KAGRA" planned to begin observation in earnest next year.

The University of Tokyo and a Japanese manufacturer made 4 mirrors for "KAGRA", and on the 21st one of them was made public at the University of Tokyo.

It was 22 centimeters in diameter and 15 centimeters in thickness and the material used was "sapphire".

"KAGRA" which could observe gravity wave was a large facility with construction advanced by the University of Tokyo at the underground at Hida-shi, Gifu. It was 3 kilometers in length by combining two pipes arranged in L letter shape. The mechanism inside would reflect laser beam at both ends by lens and making it go back and forth.

When the gravity wave was being transmitted from the universe, inside the 3 kilometers pipe it distorted a little bit, and during the round trip time the laser beam that ran through the inside would change subtly, it was then possible to detect the gravity wave.

Gravity wave was transmitted with expanding and contracting changes within a space of smaller than a hydrogen atom, the mirror which reflected the laser needed very high precision. In KAGRA the mirror was cooled to approximately 250 degrees below freezing point, and it was said that the world's pioneer technology was adopted which suppressed the occurrence of error and noise to the absolute limit. The University of Tokyo would install the mirror from now on, and plan on beginning the observation in earnest next year.

Eiichi Hirose the Associate Professor of the University of Tokyo Institute of Cosmic-Ray Research said that "at last the mirror completes the facility and now it enters the mode to observe the gravity wave. I would like to chase the space mystery that mankind doesn't know."

Time and space “distortion" occurred during a super nova explosion, and also collision between the heavenly bodies, the gravity wave was such a phenomenon which was transmitted like a wave and Einstein expected its existence; so far the United States and European facilities had succeed in its observation. It was said that it would lead to the elucidation of the mystery on the formation of the universe, and from now on some achievement from KAGRA was expected.

          It is nice to know the Japan could also observe the gravity wave on its own.