１３５億年前の銀河か　ウェッブ宇宙望遠鏡

【ワシントンＡＦＰ＝時事】ジェームズ・ウェッブ宇宙望遠鏡が捉えた画像に写っている銀河は、１３５億年前のものかもしれない──。米航空宇宙局（ＮＡＳＡ）が一連の画像を公開して１週間後の１９日、データを分析した研究者がＡＦＰに明らかにした。（写真はジェームズ・ウェッブ宇宙望遠鏡が観測した、最も遠いところにある銀河「ＧＬＡＳＳ－ｚ１３」とみられる画像）
　ハーバード大学天体物理学センターのローハン・ナイドゥ氏はＡＦＰに、「ＧＬＡＳＳ－ｚ１３と呼ばれる銀河は、ビッグバンから３億年後のもので、これまでに確認されている銀河よりおよそ１億年古いとみられる」と話した。
　「私たちが目にしているのは、人類が見た中で最も遠いところから届いた星々の光である可能性がある」
　ＧＬＡＳＳ－ｚ１３は宇宙誕生の初期に存在したが、正確なことは分かっていない。１３８億年前のビッグバンの後、３億年ほどの間に形成された可能性があるとされる。現在観測できる最も初期の宇宙は、ビッグバンから約３億３０００万年後のもの。
　ＧＬＡＳＳ－ｚ１３は、ウェッブ宇宙望遠鏡に搭載されている赤外線観測機能「ＮＩＲｃａｍ」で観測された。赤外線を可視スペクトルに変換すると、「ディープフィールド」と呼ばれる深宇宙領域を捉えた画像の一部に赤い固まりがあり、中央部分が白く写っていた。
　ナイドゥ氏が加わっている世界中の天文学者２５人から成る研究チームは、今回の調査結果を査読前論文として科学雑誌に投稿。すでに世界中の天文学界で話題になっている。
　ナイドゥ氏は、別の天文学者チームも同じデータから同様の結論に至っているとして、「今回の発見に自信を持っている」と話した。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2022/07/21-14:33）

Just a week after its first images were shown to the world, the James Webb Space Telescope may have found a galaxy that existed 13.5 billion years ago, a scientist who analyzed the data said Wednesday.
Known as GLASS-z13, the galaxy dates back to 300 million years after the Big Bang, about 100 million years earlier than anything previously identified, Rohan Naidu of the Harvard Center for Astrophysics told AFP.
We're potentially looking at the most distant starlight that anyone has ever seen, he said.
The more distant objects are from us, the longer it takes for their light to reach us, and so to gaze back into the distant universe is to see into the deep past.
Though GLASS-z13 existed in the earliest era of the universe, its exact age remains unknown as it could have formed anytime within the first 300 million years.
GLASS-z13 was spotted in so-called early release data from the orbiting observatory's main infrared imager, called NIRcam -- but the discovery was not revealed in the first image set published by NASA last week.
When translated from infrared into the visible spectrum, the galaxy appears as a blob of red with white in its center, as part of a wider image of the distant cosmos called a deep field.
Naidu and colleagues -- a team totaling 25 astronomers from across the world -- have submitted their findings to a scientific journal.
For now, the research is posted on a preprint server, so it comes with the caveat that it has yet to be peer-reviewed -- but it has already set the global astronomy community abuzz.
Astronomy records are crumbling already, and more are shaky, tweeted NASA's chief scientist Thomas Zurbuchen.
Yes, I tend to only cheer once science results clear peer review. But, this looks very promising, he added.
Naidu said another team of astronomers led by Marco Castellano that worked on the same data has achieved similar conclusions, so that gives us confidence.
- 'Work to be done' -
One of the great promises of Webb is its ability to find the earliest galaxies that formed after the Big Bang, 13.8 billion years ago.
Because these are so distant from Earth, by the time their light reaches us, 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.
Naidu and colleagues combed through this infrared data of the distant universe, searching for a telltale signature of extremely distant galaxies.
Below a particular threshold of infrared wavelength, all photons -- packets of energy -- are absorbed by the neutral hydrogen of the universe that lies between the object and the observer.
By using data collected through different infrared filters pointed at the same region of space, they were able to detect where these drop-offs in photons occurred, from which they inferred the presence of these most distant galaxies.
We searched all the early data for galaxies with this very striking signature, and these were the two systems that had by far the most compelling signature, said Naidu.
One of these is GLASS-z13, while the other, not as ancient, is GLASS-z11.
There's strong evidence, but there's still work to be done, said Naidu.
In particular, the team wants to ask Webb's managers for telescope time to carry out spectroscopy -- an analysis of light that reveals detailed properties -- to measure its precise distance.
Right now, our guess for the distance is based on what we don't see -- it would be great to have an answer for what we do see, said Naidu.
Already, however, the team have detected surprising properties.
For instance, the galaxy is the mass of a billion Suns, which is potentially very surprising, and that is something we don't really understand given how soon after the Big Bang it formed, Naidu said.
Launched last December and fully operational since last week, Webb is the most powerful space telescope ever built, with astronomers confident it will herald a new era of discovery.