2026年9月28日号

Deep underground, the LZ detector waits for dark matter to bump into a xenon atom. It recently recorded one single, unexplained hit, at 248 kiloelectronvolts. Its significance is intriguing, not a discovery.

The blow was far too strong for ordinary dark matter. Unless it weighs over 74 times a proton — an option already largely ruled out.

One idea: tiny black holes born after the Big Bang, slowly evaporating. They would spray out very fast, light particles. A physicist in India ran the numbers.

Verdict: impossible. Such black holes would also cause many small hits, and LZ saw none. Bonus: at most a millionth of dark matter can be this kind of black hole.

Source: Limits on Primordial Black Hole Evaporation from LUX-ZEPLIN, https://arxiv.org/abs/2609.29462

At the heart of some galaxies, a giant black hole shoots jets of matter across space. Seen by radio telescopes, these are radio galaxies.

An Italian-led team hunted for the most distant ones. Using the VLT in Chile, they confirmed one: TXS 2354+015, at redshift 4.946.

At 500 megahertz, it emits 6.2 × 10²⁹ watts per hertz. That is about twice the previous record. It is now the most powerful radio galaxy known.

It is also the second most distant ever found. Most of these monsters hide behind dust. Many more may be waiting. The team's method, based on how early galaxies vanish in some colours, finds them where the classic radio test fails.

Source: The quest for high-redshift radio galaxies II. Discovery of the most powerful known radio galaxy at z=4.946, https://arxiv.org/abs/2609.28632

The surface of the Sun boils. Cells of hot gas rise, cool and sink again. Simulations predicted tiny whirlpools in between. No telescope could see them. The sharpest earlier views reached about 150 kilometres.

Until DKIST, the 4-metre solar telescope in Hawaii. It filmed a small patch of the Sun for 3.2 minutes, 740 images per second.

Result: 201 whirlpools detected. Their typical width: 38.6 kilometres. More than 99% are under 50. Each turns about once every 37 seconds.

These whirlpools could carry energy upward and help heat the Sun's atmosphere. The team now wants to catch them higher up.

Source: DKIST unveils MHD-predicted sub-50 km photospheric vortices, https://arxiv.org/abs/2609.30051

When a massive star dies, it can leave a black hole. Most of them drift alone through the Galaxy. Almost impossible to see. In our Galaxy, only about two dozen black holes are known, nearly all with a companion star.

A team at Nanjing University built a simulation of the Milky Way's whole history: stars, couples of stars, explosions and orbits.

Result: about 40 million lonely black holes. Around 80,000 lie within 1 kiloparsec of the Sun, roughly 3,300 light-years. So far, only one has been confirmed.

How to find the others? They bend the light of stars behind them. The future Roman space telescope could catch hundreds of such events.

Source: A Census of Stellar-mass Black Holes in the Milky Way with POPKIN. I. Isolated Black Holes, https://arxiv.org/abs/2609.29211

いまやAIが、ボディカメラの映像から警察の報告書を書いている。その誤りは人間が見抜くことになっている。だが、もしその誤りが人間の側を変えてしまうとしたら?

研究者たちはChatGPTとGeminiに、車が歩行者をはねる25秒の動画を要約させた。20件の要約のうち19件で、衝突そのものが抜け落ちていた。

次に328人がその動画を見た。翌日、誤った交通標識が書かれた要約を読むと、正しい標識を覚えていたのは44.8%にとどまった。正しい要約を読んだ場合は83.6%だった。

人間が書いたと信じても何も変わらなかった。AIを信用していなくても同じだった。AIが間違えると知っていても、記憶は守られなかった。著者らは警察活動でのAI要約の利用に疑問を投げかけている。

出典：AI-Enabled Human Memory Manipulation: Misleading AI-Generated Summaries Distort Human Memory, https://arxiv.org/abs/2609.28820

To make green hydrogen, we split water. One key step only works with iridium or ruthenium. These metals are rare, with fragile supply chains.

A US company built a robot lab steered by AI. It tested 2,942 materials made from 26 elements, about 240 per week. Humans only move the samples.

Surprise: the winners are rich in palladium, a family nobody expected. The best one lasted 1,000 hours and kept 96% of its palladium.

Palladium is also precious, but produced more than ten times more than iridium. A chatbot alone did worse than random at this search.

Source: AI-guided high-throughput discovery of iridium- and ruthenium-free palladium-oxide catalysts for durable acidic oxygen evolution, https://arxiv.org/abs/2609.30133

Crease a sheet of paper, and it remembers that fold forever. So one origami usually makes only one shape. Tiny motors at every hinge are one known fix.

A team at Harvard slipped a steel strip, 0.05 mm thick, across each hinge. Squeezed, it bows up or down. Press it, and it flips.

Each flip decides if a fold goes up or down. One sheet folds into a bird or a whale. Another into a box or a boat. A chain spells ORIGAMI.

Some sheets even reprogram themselves when you fold their edges. One unfolds on its own when pulled. Another counts how often it has been squeezed.

Source: Reprogrammable origami through bistable buckled hinges, https://arxiv.org/abs/2609.28790

Quantum sensors use tiny magnets called spins to measure magnetic fields. The more spins you pack in, the more sensitive the sensor. In theory.

In practice, crowded spins disturb each other. Their quantum state collapses too fast. So diamond sensors keep them rare, a few to tens of parts per million.

A Berkeley-led team grew pink crystal needles where one molecule in three is a sensor. That is over 100 times denser than the benchmarks.

At room temperature, the spins stay coherent for about a microsecond. The secret: a neighbour molecule that blocks their energy from hopping around. Next step: turning these needles into real magnetic sensors.

Source: Dense pentacene cocrystal demonstrates room-temperature coherent control, https://arxiv.org/abs/2609.28912

配達ドローンや空飛ぶタクシーが、世界中の都市にやって来ようとしている。その騒音は上から降ってくる。現在の騒音規制は道路と空港を想定して書かれたものだ。しかもドローンは、同じ音量でも交通騒音より人をいらだたせるようだ。

ロンドンの研究者たちが、東京からナイロビまで10都市の上空で同一の飛行をシミュレーションした。同じルート、高度100メートル、同じ交通量である。

交通量の多い通りでは、変化は小さかった。すでに道路の騒音がかき消してしまうからだ。ロンドンとニューヨークの静かな中庭では、騒音が20デシベル以上跳ね上がった。

飛行高度に近い上層階は、下層階よりうるさくなることがある。研究チームは、今後の飛行ルートは3次元で検証する必要があるとしている。

出典：Low-altitude aircraft will reshape noise exposure across global cities, https://arxiv.org/abs/2609.29763

52枚のトランプをよく切る。最初のエースが出るまで1枚ずつ表にしていく。平均で何枚になるだろう? 予想してみてほしい。これはノルウェーの統計雑誌に載ったパズルだ。

答えは10.6枚。あるノルウェーの統計学者が、これをいくつもの方法で証明している。一般の公式は単純で、「カードの枚数+1」を「エースの枚数+1」で割ればよい。

さらに面白いことに、4枚のエースは平均すると山札を5つの等しい部分に分ける。エースとエースの間の間隔は、どれも最初の間隔と同じようにふるまう。

問いを逆にすると、これが役に立つ。1000人がいる部屋で、出会った50人目が5人目の左利きだったなら、左利きはおよそ85人いる。

出典：How many cards, until the first ace: variations, extensions, lachrymae, confidence, Dirichlets, https://arxiv.org/abs/2609.29596