罕見的“超級火焰”有一天會威脅到地球 Rare ‘superflares’ could one day threaten Earth

新聞稿11-Jun-2019
罕見的“超級火焰”有一天會威脅到地球

科羅拉多大學博爾德分校

近年來，探測銀河系邊緣的天文學家觀測到銀河系中一些最輝煌的煙火表演：超級火焰。

這些事件發生在恆星由於科學家們仍然不理解的原因而噴射出數百光年以外可以看到的巨大能量爆發時。直到最近，研究人員才認為這種爆炸主要發生在與地球不同的恆星上，這些恆星是年輕而活躍的。

現在，新的研究表明，比以往任何時候都更有信心，超級火焰可以出現在像我們自己這樣的較老的，更安靜的恆星上 – 雖然更少，或者幾乎每隔幾千年一次。

研究的第一作者，CU Boulder的訪問研究員Yuta Notsu表示，這一結果應該是我們星球上生命的警鐘。

他說，如果一個超級火焰從太陽噴發出來，地球很可能會坐在一股高能輻射的道路上。這樣的爆炸可能會擾亂全球各地的電子設備，造成大規模的黑屏並縮短軌道上的通信衛星。

Notsu在聖路易斯舉行的美國天文學會第234次會議的新聞發布會上介紹了他的研究成果。

“我們的研究表明，超級火焰是罕見的事件，”CU博爾德大氣與空間物理實驗室的研究員Notsu說。 “但在未來100年左右，我們有可能會遇到這樣的事件。”

科學家們首先從一個不太可能的來源發現了這種現象：開普勒太空望遠鏡。美國宇航局於2009年發射的太空船尋找繞地球遠離恆星的行星。但它也發現了這些明星本身的奇怪之處。在罕見的事件中，來自遙遠恆星的光似乎突然變得越來越明亮。

研究人員稱這些巨大的能量爆發為“超級火焰”。

Notsu解釋說，正常大小的耀斑在太陽下很常見。但是，開普勒數據顯示的數據似乎要大得多，比地球上現代儀器記錄的最大火炬強大幾百到幾千倍。

這提出了一個顯而易見的問題：在我們自己的太陽上是否還會發生超級火焰？

“當我們的太陽很年輕時，它非常活躍，因為它旋轉速度非常快，可能產生更強大的耀斑，”Notsu說，他也是博爾德國家太陽天文台。 “但我們不知道現代太陽上是否會出現如此大的耀斑，頻率非常低。”

為了找到答案，Notsu和一個國際研究團隊轉向了來自歐洲航天局蓋亞宇宙飛船和新墨西哥州Apache Point天文台的數據。在一系列研究中，該小組利用這些工具縮小了一組來自43顆類似於我們太陽的恆星。然後，研究人員對這些罕見事件進行了嚴格的統計分析。

底線：年齡問題。根據團隊的計算，年輕的明星往往會產生最多的超級明星。但像我們的太陽這樣的老星，現在已經有了46億年的歷史，並沒有擺脫困境。

“年輕的明星每週都有一次超級明星，”Notsu說。 “對於太陽來說，它平均每隔幾千年一次。”

該小組於5月在“天體物理學雜誌”上發表了最新的研究結果。

Notsu無法確定下一次大型太陽能燈展會是否會襲擊地球。但他說這是時間問題，而不是問題。儘管如此，這仍然可以讓人們有時間準備，保護地面和軌道上的電子設備免受太空輻射的影響。

“如果一個超級火焰發生在1000年前，那可能不是什麼大問題。人們可能已經看到了一個巨大的極光，”Notsu說。 “現在，由於我們的電子產品，這是一個更大的問題。”

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最近研究的共同作者包括來自京都大學，日本國家天文台，兵庫大學，華盛頓大學和萊頓大學的研究人員。

News Release 11-Jun-2019
Rare ‘superflares’ could one day threaten Earth

University of Colorado at Boulder

Astronomers probing the edges of the Milky Way have in recent years observed some of the most brilliant pyrotechnic displays in the galaxy: superflares.

These events occur when stars, for reasons that scientists still don’t understand, eject huge bursts of energy that can be seen from hundreds of light years away. Until recently, researchers assumed that such explosions occurred mostly on stars that, unlike Earth’s, were young and active.

Now, new research shows with more confidence than ever before that superflares can occur on older, quieter stars like our own–albeit more rarely, or about once every few thousand years.

The results should be a wake-up call for life on our planet, said Yuta Notsu, the lead author of the study and a visiting researcher at CU Boulder.

If a superflare erupted from the sun, he said, Earth would likely sit in the path of a wave of high-energy radiation. Such a blast could disrupt electronics across the globe, causing widespread black outs and shorting out communication satellites in orbit.

Notsu presented his research at a press briefing at the 234th meeting of the American Astronomical Society in St. Louis.

“Our study shows that superflares are rare events,” said Notsu, a researcher in CU Boulder’s Laboratory for Atmospheric and Space Physics. “But there is some possibility that we could experience such an event in the next 100 years or so.”

Scientists first discovered this phenomenon from an unlikely source: the Kepler Space Telescope. The NASA spacecraft, launched in 2009, seeks out planets circling stars far from Earth. But it also found something odd about those stars themselves. In rare events, the light from distant stars seemed to get suddenly, and momentarily, brighter.

Researchers dubbed those humungous bursts of energy “superflares.”

Notsu explained that normal-sized flares are common on the sun. But what the Kepler data was showing seemed to be much bigger, on the order of hundreds to thousands of times more powerful than the largest flare ever recorded with modern instruments on Earth.

And that raised an obvious question: Could a superflare also occur on our own sun?

“When our sun was young, it was very active because it rotated very fast and probably generated more powerful flares,” said Notsu, also of the National Solar Observatory in Boulder. “But we didn’t know if such large flares occur on the modern sun with very low frequency.”

To find out, Notsu and an international team of researchers turned to data from the European Space Agency’s Gaia spacecraft and from the Apache Point Observatory in New Mexico. Over a series of studies, the group used those instruments to narrow down a list of superflares that had come from 43 stars that resembled our sun. The researchers then subjected those rare events to a rigorous statistical analysis.

The bottom line: age matters. Based on the team’s calculations, younger stars tend to produce the most superflares. But older stars like our sun, now a respectable 4.6 billion years old, aren’t off the hook.

“Young stars have superflares once every week or so,” Notsu said. “For the sun, it’s once every few thousand years on average.”

The group published its latest results in May in The Astrophysical Journal.

Notsu can’t be sure when the next big solar light show is due to hit Earth. But he said that it’s a matter of when, not if. Still, that could give humans time to prepare, protecting electronics on the ground and in orbit from radiation in space.

“If a superflare occurred 1,000 years ago, it was probably no big problem. People may have seen a large aurora,” Notsu said. “Now, it’s a much bigger problem because of our electronics.”

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Co-authors on the recent study include researchers from Kyoto University, the National Astronomical Observatory of Japan, University of Hyogo, University of Washington and Leiden University.

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