Scientists Enthralled by Biggest Star Explosion Ever Observed
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April 14, 2020 12:32 PM (source)
Scientists Enthralled by Biggest Star Explosion Ever Observed
史上最大超新星吸引科學家目光
April 14, 2020 12:32 PM
Reuters
WASHINGTON —
Scientists have observed the biggest supernova - stellar explosion - ever detected, the violent death of a huge star up to 100 times more massive than our sun in a faraway galaxy.
The supernova, releasing twice as much energy as any other stellar explosion observed to date, occurred about 4.6 billion light years from Earth in a relatively small galaxy, scientists said. A light year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).
It might represent, they added, a type of supernova that until now has only been theorized.
Astrophysicist Matt Nicholl of the University of Birmingham in England said two very massive stars - each about 50 times the sun's mass - may have merged to make one extremely massive star roughly 1,000 years before the explosion. They had been part of what is called a binary system with two stars gravitationally bound to each other.
The merged star exploded in a supernova, formally named SN2016aps, inside a very dense and hydrogen-rich envelope.
"We found that the supernova was able to become so bright because of a powerful collision between the debris ejected by the explosion and a shell of gas shaken off by the star a few years earlier," said Nicholl, lead author of the study published this week in the journal Nature Astronomy.
Stars die in various different ways depending on their size and other properties. When a massive star - more than eight times the mass of our sun - uses up its fuel, it cools off and its core collapses, triggering shock waves that cause its outer layer to explode so violently that it can outshine entire galaxies.
The researchers, who observed the explosion for two years until it diminished to 1 percent of its maximum brightness, said it may have been an example of an extremely rare "pulsational pair-instability" supernova.
"Pulsational pair-instability is when very massive stars undergo pulsations which eject material away from the star," said study co-author Peter Blanchard, a postdoctoral fellow in astrophysics at Northwestern University in Illinois.
"This discovery shows that there are many exciting and new phenomena left to be uncovered in the universe,” Blanchard added.
Very massive stars like this one were probably more common early in the universe's history, Nicholl said.
"The nature of those first stars is one of the big questions in astronomy," Nicholl added. "In astronomy, seeing things further away means looking back further and further in time. So we might actually be able to see the very first stars if they explode in a similar manner to this one. Now we know what to look for."
科學家觀測到有史以來最大的超新星(supernova)，也就是所謂的恆星爆炸(stellar explosion)。這顆位在遙遠星系(galaxy)的巨大恆星在劇烈死亡(violent death)前的質量重達太陽的 100 倍。
科學家表示，超新星發生在距離地球約 46 億光年的較小星系中，其釋放的能量是迄今觀測到的任何其他恆星爆炸的兩倍。光年是光在一年中傳播的距離，即 5.9 兆英里（9.5 兆公里）。
他們補充說，這結果可能顯示科學家今日才確立一類超新星的理論。
英國伯明罕大學（University of Birmingham）的天體物理學家(astrophysicist，註 1)馬特．尼古爾（Matt Nicholl）提到，宇宙中兩顆非常巨大的恆星，其質量各別約是太陽質量的 50 倍，這兩顆恆星在爆炸發生前的 1000 年左右合併(merge)成極為巨大的恆星；這些恆星曾經是雙(binary)星系統的一部分，受到引力牽引(gravitationally，註 2)，系統中兩顆恆星彼此相連(bound，註 3)。
合併後的恆星最終爆炸，形成超新星，這顆超新星的正式名稱為SN2016aps，且被非常濃密且富含氫氣的外層所包覆。
這項研究結果發表於《自然天文學》（Nature Astronomy）期刊上，主要研究員尼古爾表示：「我們發現：超新星之所以能夠變得這麼明亮，原因在於爆炸所噴射出的碎片與恆星幾年前甩開的氣體殼兩者之間發生了強烈的碰撞」
星體大小和其他特性(property)會使恆星以各種不同的方式死亡：質量超過太陽質量 8 倍的巨大恆星在燃燒殆盡後就會冷卻下來，同時因核心坍塌，觸發(trigger，註 4)了衝擊波(shock wave)，造成外層猛烈爆炸，造成其形成的亮度超過(outshine)了整個星系。
研究人員對恆星爆炸持續觀察了兩年，直到其減少(diminish，註 5)到最大亮度的 1%，他們指出，這個例子可能是極為罕見的「脈動式成對不穩定性」（pulsational pair-instability）超新星。
美國伊利諾州（Illinois）西北大學（Northwestern University）的天體物理學(astrophysics)博士後研究員彼得．布蘭查德（Peter Blanchard）共同參與了這項研究。他進一步解釋：「脈動式成對不穩定性是指非常巨大的恆星經受(undergo，註 6)劇烈震動(pulsation，註 7)，進而將物質從恆星中噴射出來。」
布蘭查德補充說：「這個發現表示宇宙中還有許多令人興奮的新現象(phenomena，註 8)尚待發現(uncover)。」
尼古爾指出，類似這樣巨大的恆星可能在宇宙形成初期更為常見。
「最早出現恆星的特性(nature)是天文學主要探究的問題之一。」尼古爾補充說明：「天文學中，當觀測到的事物距離越遠，意味著時間越加久遠，因此，如果早期恆星以相似的方式爆炸，實際上可能有機會觀測到。現在我們終於知道該尋找什麼了。」
Language Notes
註 1： astrophysicist 為名詞，指「天體物理學家」；本字由字首 "astro-"「星的；星狀的；太空的」與名詞 "physicist"「物理學家」組成；注意重音在第 3 音節；相關名詞為 "astrophysics"「天體物理學」
註 2： gravitationally 由形容詞 "gravitational"「（萬有）引力的；重力的」與副詞字尾 "-ly"「以所述的方式」組成；注意重音在第 3 音節
註 3：bound 於本文為形容詞，意思是「與 . . . . . . 相連的」；本字源於動詞 "bind"「捆綁；捆紮」
註 4： trigger 於本文作動詞，指「引起，引發（壞事）」；本字也可作名詞，常指「（槍的）扳機」或「（引起某種壞事的）一件事（或情況）」
註 5： diminish 為動詞，意指「減少，減小，降低」；本字另可指「削弱 . . . . . . 的權勢；降低 . . . . . . 的聲譽」；注意重音在第 2 音節
註 6： undergo 為動詞，指「 經歷，經受（令人不快的事或變化）」；本字另常見的意思為「接受（治療、檢查等）」；注意重音在第 3 音節
註 7： pulsation 為名詞，意指「劇烈震動；劇烈脈動」；注意重音在第 2 音節；相關形容詞為 "pulsational"「震動的；脈動的」
註 8： phenomena 的意思是「（尤指不尋常的或有趣的）現象」，為名詞 "phenomenon" 的複數形；本字也常指「非凡的人（或事物）；奇才；奇跡」；注意重音在第 2 音節；相關形容詞為 "phenomenal"「非凡的；傑出的」
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Check your comprehension!
Choose the BEST answer to each of the questions below. After you finish, highlight the parentheses to reveal the hidden answers.
1. ( D ) According to the article, why was the supernova able to become so bright?
(A) Because of a shell of gas being dislodged by the galaxy.
(B) Because of shock waves generated by the collapse of the massive star's core.
(C) Because of the explosion within a very dense and hydrogen-rich envelope.
(D) Because of the compelling collision between debris discharged by the explosion.
2. ( B ) According to the article, which of the following statement is INCORRECT?
(A) The supernova occurred in a relatively small galaxy about 4.6 billion light years from Earth.
(B) Very enormous stars can withstand pulsation when materials are dislodged away from the galaxy. (C) The two enormous stars merged to make an extremely massive star about 1000 years before the explosion.
(D) Stars perish in different ways depending on their size and other features.
3. ( A ) The word "nature" in the last paragraph is closest in meaning to:
(A) characteristic
(B) variety
(C) personality
(D) environment
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