ウェッブ望遠鏡、最古の銀河確認 ビッグバン後２億９０００万年のもの

【ワシントンＡＦＰ＝時事】米航空宇宙局（ＮＡＳＡ）は３０日、ジェームズ・ウェッブ宇宙望遠鏡が、これまで確認されている中で最も古い銀河を発見したと発表した。発見された銀河は、１３８億年前に宇宙が誕生したビッグバンから２億９０００万年後のものとされる。（写真は、ジェームズ・ウェッブ宇宙望遠鏡が撮影した、これまで確認されている中で最古の銀河。搭載する近赤外線カメラＮＩＲＣａｍで撮影）
　２０２２年に稼働を開始したウェッブ宇宙望遠鏡による新たな発見について研究者らは、いわゆる「宇宙の夜明け」を理解する上で「重大な意味」を持つと指摘している。
　ＮＡＳＡによると、今回発見されたのは「ＪＡＤＥＳ－ＧＳ－ｚ１４－０」と呼ばれる銀河で、２０２３年前半には確認されていたが、その年代を確定するためにさらなる観測を要した。
　「ＪＡＤＥＳ－ＧＳ－ｚ１４－０」は、地球からの距離のわりに明るかったため、研究者らを驚かせた。
　遠くの銀河から出た光は、地球に到達する時点で宇宙の膨張によって引き伸ばされるため、スペクトルの赤外線領域で観測する必要がある。ウェッブ宇宙望遠鏡には赤外線カメラが搭載されている。
　研究チームは昨年１０月と今年１月に行った観測で、「ＪＡＤＥＳ－ＧＳ－ｚ１４－０」がこれまで最も遠い銀河とされた「ＪＡＤＥＳ－ＧＳ－ｚ１３－０」よりも古いことを確認した。「ＪＡＤＥＳ－ＧＳ－ｚ１３－０」は、ビッグバンから３億２０００万年後のもの。
　また観測データから「ＪＡＤＥＳ－ＧＳ－ｚ１４－０」は、１６００光年の大きさがあることが分かった。研究者らは「この光から、銀河の質量が太陽の数億倍あることが推測される」としている。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2024/05/31-18:14）

The James Webb Space Telescope has discovered what appears to be a new record-holder for the most distant known galaxy, a remarkably bright star system that existed just 290 million years after the Big Bang, NASA said Thursday.
Since coming online in 2022, the Webb telescope has ushered in a new era of scientific breakthroughs, peering farther than ever before into the universe's distant reaches -- which also means it is looking back in time.
And the latest finding has profound implications for our understanding of the so-called Cosmic Dawn, researchers said.
An international team of astronomers first spotted the galaxy called JADES-GS-z14-0 in early 2023, but they needed further observations to be sure it really was a record-breaker rather than a confounding oddball, they said in a joint statement.
The source was surprisingly bright, which we wouldn't expect for such a distant galaxy, and it was very close to another galaxy such that the two appeared to be part of one larger object, said Stefano Carniani from Scuola Normale Superiore in Italy and Kevin Hainline from the University of Arizona.
By the time light from the most distant galaxies reaches Earth, it has been stretched by the expansion of the universe and shifted to the infrared region of the light spectrum, which Webb is equipped to detect with unprecedented clarity.
The team carried out confirmatory observations in October and then January -- first with Webb's primary imager called NIRCam, and second with its NIRSpec that analyzes the spectrum of light from an object to determine its physical properties -- to be more certain of their hypothesis.
JADES-GS-z14-0 comfortably beats the previous record for oldest known galaxy, which was held by JADES-GS-z13-0 that was present 320 million years after the Big Bang.
Once its age was confirmed in January, I had to stand up away from my computer, it just felt so ridiculous to see this, Hainline said in a video posted to YouTube.
If the universe were a two-hour movie, this galaxy is from the first two and a half minutes, he added.
- Predictions upended -
The most important aspect of JADES-GS-z14-0 was that at this distance, we know that this galaxy must be intrinsically very luminous, said Carniani and Hainline.
From the images, the galaxy was determined to be 1,600 light years across, suggesting that the light is coming from mostly young stars and not from emission near a growing supermassive black hole.
This starlight implies that the galaxy is several hundreds of millions of times the mass of the Sun! said the researchers. This raises the question: How can nature make such a bright, massive, and large galaxy in less than 300 million years?
Further analysis of the light emissions indicates the presence of oxygen, another surprising finding that points to multiple generations of very massive stars had already lived their lives before we observed the galaxy.
Taken together, the observations of JADES-GS-z14-0 upend astronomical predictions of what the earliest galaxies may have looked like following the Big Bang 13.8 billion years ago.
Given the relatively small portion of the night sky they looked at, it's highly likely more luminous galaxies at possibly even earlier times will be found in the coming years, said the researchers, who will now look to publish their findings in a peer-reviewed journal.