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那些“死去”的小星系是如何恢复到原来的状态并重新形成恒星的呢

  Gas falling into the dwarf galaxy must fight the galaxy’s old stars before making new ones

  落入矮星系的气体必须先与旧恒星斗争,然后才能形成新的恒星

  Unlike most of its tiny peers,little Leo P glitters with freshly minted stars,From left to right,this Hubble image spans just 4,800 light-years,showing how small Leo P is.

  与大多数小星系不同,狮子座P星系(Leo P)闪烁着明亮而散发蓝色光芒的新恒星。从左至右,这张哈勃影像仅跨越4,800光年,显示了狮子座P星系是多么的小。

  Talk about sibling rivalry.Most of the smallest galaxies are“dead,”making no new stars.Now,computer simulations reveal why it is so hard for a tiny galaxy to rejuvenate itself:The galaxy’s existing stars fight the birth of any new ones,even after fresh fuel for star formation falls into the galaxy.

  说说“兄弟姐妹”间的竞争。大多数非常小的星系已经“死亡”,没有产生新的恒星。现在,计算机模拟揭示了为什么一个小星系很难产生新的恒星:星系中现有的恒星会与任何新恒星的诞生作斗争,甚至在恒星形成的“新燃料”落入星系后也是如此。

  These simulations also show that eventually new stars can arise and make the galaxy sparkle again.But it can take many billions of years for a little galaxy to get its star-making mojo back,researchers report April 20 at arXiv.org.

  这些模拟还显示,尽管如此,最终仍会有新的恒星出现,让星系再次“闪耀”。但研究人员4月20日在arXiv.org上报告说,一个小星系要恢复其造星的能力可能需要数十亿年的时间。

  星系从气体中产生了新的恒星,但是这些气体必须是冷的和稠密的才能坍缩成恒星

  Galaxies spawn new stars from gas,but the gas must be cold and dense to collapse into stars.That requirement spelled big trouble for little galaxies soon after the universe’s birth,when ultraviolet radiation from galaxies broke intergalactic hydrogen atoms into protons and electrons(SN:11/7/19).This process,called reionization,let radiation stream through space and heat gas inside galaxies.The smallest galaxies had so little gas to begin with that it all got zapped by the ionizing radiation.As a result,the typical low-mass dwarf galaxy stopped creating stars long ago.

  星系从气体中产生了新的恒星,但是这些气体必须是冷的和稠密的才能坍缩成恒星。这一要求给宇宙诞生后不久的小星系带来了大麻烦,当时来自星系的紫外线辐射将星系间的氢原子分解成质子和电子(SN:11/7/19).这个过程被称为电离,让辐射流穿过空间,加热星系内部的气体。最小的星系一开始几乎没有气体,所以都受到了电离辐射的影响。结果,典型的低质量矮星系很久以前就停止了恒星的产生。
纽约时报中英文网 http://www.qqenglish.com/


  In these tiny galaxies,“reionization killed star formation,”says Martin Rey,an astrophysicist at Lund Observatory in Sweden.All the stars in most low-mass dwarf galaxies today are therefore ancient(SN:4/3/15).

  瑞典隆德天文台的天体物理学家Martin Rey说,在这些微小的星系中,“电离阻止了恒星的形成”。因此,今天大多数低质量矮星系中的所有恒星都是古老的(SN:4/3/15).

  但是狮子座的两个不相关的矮星系,名为狮子座P和狮子座T,从来没有得到过注意

  But two unrelated dwarf galaxies in the constellation Leo,named Leo P and Leo T,never got the memo.Puny even by dwarf standards,both galaxies still eke out new stars.They are the least luminous star-forming galaxies known:Leo P’s stellar mass is only 560,000 solar masses,about 0.001 percent of the Milky Way’s total,and Leo T has even fewer stars(SN:5/9/18).Both galaxies are the Milky Way’s neighbors—Leo P is 5 million light-years and Leo T is just 1.3 million light-years away—so astronomers can see the newborn stars.

  但是狮子座的两个不相关的矮星系,名为狮子座P和狮子座T,从来没有得到过注意。即使以矮星系的标准来衡量,这两个星系仍然可以勉强产生新的恒星。它们是已知的发光度最低的恒星系:Leo P的恒星质量只有560,000个太阳质量,约占银河系总量的0.001%,而Leo T的恒星甚至更少(SN:5/9/18).两个星系都是银河系的邻居,狮子座P距我们500万光年,狮子座T距我们130万光年,所以天文学家可以看到新生的恒星。

  To explain how such small galaxies thrive today,Rey’s team ran computer simulations of the gas,stars and dark matter in low-mass dwarf galaxies.The simulations showed that infalling gas can resuscitate dwarf galaxies and reignite their star formation,a finding supported by earlier work(SN:7/12/18).But“we find that it takes quite a long time,”Rey says.
纽约时报中英文网 http://www.qqenglish.com/


  为了解释今天这些小星系是如何繁衍的,Rey的研究小组对低质量矮星系中的气体、恒星和暗物质进行了计算机模拟。模拟显示,注入气体可以使矮星系“复苏”,重新点燃它们的造星能力,这一发现得到了早期工作的支持(SN:7/12/18).但Rey说,“我们发现这需要相当长的时间。”

  The problem is that old stars in the dwarf galaxy prevent the birth of new stars by stirring up the gas,the researchers found.In particular,exploding white dwarf stars and winds from large red aging stars heat the gas,delaying the new era of star birth.In fact,6 to 8 billion years—about half the age of the universe(SN:7/24/18)—can pass before little dwarf galaxies resume their star-making careers and resemble Leo P and Leo T,the scientists report.

  研究人员发现,问题在于矮星系中的老恒星通过搅动气体来阻止新恒星的诞生。特别是,爆炸的白矮星和来自大型红色老化恒星的风加热了气体,推迟了恒星诞生的新时代。事实上,要经过60至80亿年,这大约是宇宙年龄的一半(SN:7/24/18)——科学家们报告说,矮星系才能恢复其造星能力并类似于狮子座P和狮子座T。

  “Their results are very plausible,”says Kristen McQuinn,an astrophysicist at Rutgers University in Piscataway,N.J.,who has studied Leo P in the past but was not involved with the new work.She says including the negative effects of the galaxy’s own stars makes the simulations unique.

  新泽西州皮斯卡塔韦罗格斯大学的天体物理学家Kristen McQuinn说,他们的研究结果非常可信。McQuinn过去曾研究过Leo P,但没有参与这项新研究。她说,包括星系自身恒星的负面影响在内的模拟结果是独一无二的。

  Rey and his colleagues also found something else.“The kind of surprise and cherry on the cake was the fact that we can predict a new class of galaxies,”Rey says.The simulations show that some low-mass dwarf galaxies have acquired gas but not yet begun to mint new stars.

  Rey和他的同事们还发现了其他一些东西。Rey说,“我们能够预测到一个新的星系类别,这一事实给我们带来了惊喜。”模拟显示,一些低质量矮星系已经获得了气体,但还没有开始产生新的恒星。

  No definite examples of gas-rich dwarf galaxies that lack star formation are known,Rey says,but he predicts future observations will uncover them.New optical telescopes should find the faint old stars in these galaxies,and radio telescopes should detect their hydrogen gas,which may someday spawn new stars.

  Rey说,目前还不知道缺乏恒星形成的但富含气体的矮星系的确切例子,但他预测未来将会发现它们。新的光学望远镜应该能在这些星系中找到微弱的旧恒星,射电望远镜应该能探测到它们的氢气,而这些氢气有一天可能会产生新的恒星。
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