内容来源：https://www.quantamagazine.org/a-new-map-of-empty-space-challenges-a-tranquil-picture-of-the-galaxy-20261030/

内容总结：

最新研究发现，星际介质远比此前认为的复杂多变，这一结果对教科书中的经典理论模型构成了直接挑战，并可能为恒星形成效率长期偏低这一难题提供解释。

长期以来，天文学家普遍将星际介质——即恒星之间由氢、氦及其他中性原子组成的稀薄气体——视为宇宙中静止不变的背景。2020年，美国宇航局“新视野”号探测器在飞越冥王星轨道后测算发现，银河系星际介质中每升空间约含130个氢原子。由于星际介质极为稀薄、变化缓慢，过去半个世纪以来，天文学家大多忽略其细节。

然而，近年来天体物理学家利用跨越数千光年的新型三维地图，发现星际介质的大部分处于不稳定的中间状态，而非理论预测的冷、暖两种稳定状态之一。1969年，科学家提出星际介质存在冷态（约100开尔文）和暖态（约8000开尔文）两种稳定状态，并认为原子几乎瞬间完成状态转换，不会留下不稳定的中间介质。1977年，另有学者补充了超新星激波前沿的高温等离子体相，但仍假设激波区之外的原子气体处于平稳的压强平衡状态。

由于冷原子氢不发射可见光，测量难度极大。天文学家70多年来依靠探测21厘米波长的微弱射电信号进行观测，但从地球单一视线方向只能收到多层云气信号叠加的混杂结果，难以拆分。2013年发射的“盖亚”望远镜通过视差法测量了近20亿颗恒星的距离，并结合星光穿越星际介质时的变暗和变红情况，帮助科学家构建了太阳周围4000多光年范围内星际尘埃密度的三维地图。2024年，研究团队进一步将尘埃密度图与紫外辐射强度图结合，在三维网格上逐点比对，以判断星际介质的冷热分布。

结果显示，在银河系邻近区域，27%的星际介质为冷态，32%为暖态，其余41%处于理论上的“禁区”——不稳定的中间状态。研究人员表示，这些不稳定介质形成了包裹冷云的大型连贯结构。同行评价认为，这表明有某种机制在不断搅动本应处于稳定状态的物质，使星际介质始终处于能量流动与状态转换之中。

针对上述发现，有学者提出谨慎态度，认为模型可能因冷暖区域过于接近而高估不稳定介质的比例，或所用“系综平均”方法在计算中平滑了密度骤变，从而人为放大了不稳定成分。研究团队承认分辨率和地图平滑存在局限，但表示在分辨率更低的另一份尘埃地图上测试时，不稳定比例仅变化约5%，数学模糊不足以解释大部分不稳定介质。

该发现还可能解释星系将气体和尘埃转化为恒星效率极低这一长期难题。天文学家指出，星际介质反复加热与冷却的循环过程会抑制恒星形成，经典模型假设星际介质处于平静平衡态，因而与现实不符——模型提供的是“有物理依据的快照”，但快照之间仍有大量动态过程发生。目前，相关论文正在接受同行评审。

中文翻译：

“空无一物”空间的新地图挑战银河系的宁静图景

引言

你或许以为太空是空无一物的。但那看似虚无的空间中，弥漫着一层几乎无法察觉的氢和其他中性原子构成的薄雾。2020年，美国宇航局的新视野号探测器在飞越冥王星轨道后，测量了周围氢含量的一个替代指标。在我们银河系恒星之间的区域——即“星际介质”（ISM）——新视野号发现每升空间约有130个氢原子。

这些氢，连同一些氦和其他分子，大部分是宇宙大爆炸的遗留物，并且不断由各种宇宙现象补充，例如恒星在诞生时喷射气体和尘埃喷流，以及在死亡时脱落外层。

由于星际介质如此稀薄、变化如此缓慢，在过去半个世纪里，天文学家基本上忽略了它的细节，将其视为宇宙中更耀眼事件的静止背景。

但大部分空无一物的空间并不像看起来那么简单。

在过去几年里，天体物理学家改变了我们对星际介质的理解。利用新绘制的跨越银河系数千光年的地图，他们发现星际介质并非研究人员所认为的那样安静、稳定的背景。相反，星际介质的很大一部分似乎是不稳定的——这一发现直接与教科书上教授的主流理论模型相矛盾。这一意外发现可能有助于解决一个长期悬而未决的问题：恒星形成的速度究竟有多快。

热与冷

1969年，研究人员乔治·菲尔德、唐纳德·戈德史密斯和哈姆·哈宾提出了一个关于星际介质行为的模型。他们预测星际介质存在于两种稳定状态：冷态和暖态。

当气体和尘埃漂浮在太空中时，它们通过引力将更多的气体和尘埃聚集在一起，最终形成云团。这些云团倾向于冷却，因为快速运动的分子会与其他分子碰撞并损失能量。它们的温度保持在刺骨的100开尔文，即约零下173摄氏度。

但有时气体和尘埃太热，无法坍缩成冷云；相反，它们形成弥散云。弥散云更容易暴露在附近恒星的影响下，恒星以紫外线辐射的形式传递新能量。这一过程使云团保持在接近8000开尔文的稳定温度。

科学家认为，星际介质中的原子几乎会立即转变为冷态或暖态，基本上不会留下不稳定的中间态星际介质。

1977年，克里斯·麦基和杰里迈亚·奥斯特里克在图中增加了第三个阶段：在超新星激波锋面处，气体可以变得更热，转变为温度达50万开尔文的炽热等离子体。然而，即使在这个扩展框架中，爆炸区域之外的原子气体也被假定处于平静的、压力平衡的存在状态。

但这很难验证该理论。冷原子氢不发射可见光。测量它的最简单方法是寻找一种罕见的原子跃迁：氢原子内的电子和质子有时会在两种可能的状态之间切换。这种跃迁会发射波长为21厘米的微弱无线电波。

70多年来，天文学家一直将射电望远镜对准天空来探测这些气体的低语，但从地球沿单一视线方向观测，他们只能收集到来自重叠云团的杂乱信号堆。梳理这些结果就像透过一叠半透明的彩色塑料片观察；它们的颜色混在一起，难以辨认任何单独的层。

直到近年来，随着新太空望远镜的发射，天文学家才能够以足够的细节探测恒星之间的空间，将这些层分离开来。

盖亚的馈赠

盖亚望远镜于2013年发射，为科学家提供了太阳周围恒星的三维地图，从而为理解星际介质创造了新机会。

你可以通过把拇指举在面前，先闭上左眼，再闭上右眼，来了解它绘制这张地图所用的一种方法。如果你来回切换，你会注意到拇指相对于其背后的物体似乎在移动。拇指离脸越近，你看到的位移就越大。这种现象叫做视差。

盖亚在地球一年一度的轨道运行中从太阳一侧移动到另一侧时，从不同角度观测了近20亿颗恒星。研究视差效应使研究人员能够确定恒星与地球的距离。

科学家随后研究了这些恒星的光在穿过星际介质到达盖亚的过程中如何变暗和变红。通过从多个角度收集这些数据，并利用通过视差收集的距离信息，科学家们得以更好地理解恒星之间尘埃的密度。

但将这些信息转化为星际介质的三维地图并不简单。中国杭州西湖大学的天文学家格雷戈里·格林表示，许多可能的星际介质构型都能满足同样的数据。更多数据为天文学家提供了更好的约束条件，但也使他们的计算更加复杂。格林说，挑战在于当底层数学“变得不可能”时，挑选出最符合物理实际的结构。

在过去十年中，格林和其他研究人员建立了先进的统计框架来应对这一计算。2024年，另一个团队利用这些工具创建了一张连续的三维地图，描绘了太阳周围直径超过4000光年的球体范围内星际介质尘埃的密度。

尘埃地图向研究人员展示了星际尘埃集中的位置，揭示了散布在恒星之间空间中的致密云团。但它无法告诉他们这些尘埃有多热或多冷。要了解星际介质温度的全貌，研究人员需要第二张地图来揭示它是如何被加热的。这张地图将来自一个意想不到的来源。

流动的状态

以色列海法理工学院的本科生乔纳森·谢莱斯特记得2024年的一次天体物理学研究研讨会，他的教授什穆埃尔·比亚利向学生们展示了聚集在恒星之间虚空中的气体和尘埃形成的翻涌结构图像，例如创生之柱。“我喜欢想象万物的几何形态，”谢莱斯特说。“自然而然地就会开始想象所有的动态、所有的结构、所有的美丽和丰富。”

讲座结束后，谢莱斯特立刻给比亚利发了邮件，请求加入他的研究小组。仿佛是命运的安排，比亚利最近一直在寻找一名学生通过三维测绘来探索星际介质，于是一段研究合作关系就此诞生。

谢莱斯特已经拥有了星际介质尘埃的地图。计划是将这张地图与一幅加热星际介质的紫外线辐射地图结合起来。

碰巧的是，比亚利在一次会议上与斯坦福大学的天体物理学家特洛伊·波特攀谈，从而找到了这样一张地图——波特已经制作了一张地图，但尚未发表。

于是，谢莱斯特、比亚利及其同事着手将两张地图中总计200吉字节的数据结合起来。在空间中的每一个点上，他们比较尘埃密度与辐射强度，以了解星际介质在哪里热、在哪里冷。最终，他们能够在一个三维网格上整合尘埃和辐射信息。

谢莱斯特随后着手研究这张地图能告诉他什么。最大的惊喜出现在他调查星际介质的整体温度时：谢莱斯特发现，在我们银河系邻域中，27%的星际介质是冷态的，32%是暖态的，其余41%恰好处于禁区内，属于不稳定介质。“我以为我搞错了，”谢莱斯特说。“你怎么去跟你的导师说，你得到了这么多不稳定介质？”

但地图似乎并没有出错。谢莱斯特在三维网格中没有看到伪影或随机统计噪声的迹象。相反，不稳定的星际介质形成了巨大的、连贯的覆盖层，将冷云完全包裹起来。

佛罗里达大学的天文学家亚当·金斯伯格表示，所有这些既不热也不冷的中间态介质意味着旧理论是不完整的。“有什么东西正在把按照静态理论应该处于另外两种状态之一的物质搅动起来，迫使它改变状态。”

佛罗里达大学的天体物理学家德西卡·纳拉亚南用了一个有机体的比喻。“就像你体内的血液会携带代谢废物或氧气，将不同的物质运送到不同的地方，”他说，“星际介质也在做同样的事情，只不过运送的是能量，而且它始终处于不断变化的状态。”

审慎的方法

2026年7月，该团队发布论文的那天，谢莱斯特的收件箱里充满了兴奋的天文学家发来的信息和合作请求。尽管如此，研究人员呼吁在改写教科书之前保持谨慎。

麦基表示，如果冷态和暖态区域距离太近，模型无法区分它们，那么模型可能高估了不稳定星际介质的数量。另外，斯坦福大学卡夫利粒子天体物理与宇宙学研究所的天体物理学家菲利普·弗兰克表示，团队用于计算气体和尘埃整体分布的方法可能误导了他们。研究人员使用了“集合平均均值”，这种计算方法自然会倾向于抹平急剧的对比。如果冷云突然过渡为暖云，这种方法会人为地将其密度的陡降软化为更平缓的坡度，从而夸大不稳定星际介质的数量。

谢莱斯特和比亚利——他们的分析目前正在接受同行评审——承认有限的分辨率和地图平滑都是问题，但他们认为仅凭数学模糊化无法解释大部分不稳定星际介质。他们说，当作者在一个完全不同的低分辨率尘埃地图上测试他们的模型时，不稳定比例仅变化了约5%。

创世的翻涌

星系在将原材料——气体和尘埃——转化为恒星方面的效率极低。几十年来，模拟一直难以解释其中的原因。新地图提供了一个答案：恒星形成受到星际介质不断翻涌的加热和冷却循环的抑制。

“恒星形成效率非常低的原因是反馈会加热并推动周围的气体，”圣迭戈州立大学的天体物理学家安娜·罗森说。这种翻涌可能解释了为什么假设星际介质处于宁静平衡状态的经典模型似乎与现实不太吻合。罗森说，这些模型给了我们“有物理依据的快照”——热态和冷态星际介质区块的不变图像——“但在这些快照之间，还有很多事情在发生。”

英文来源：

A New Map of ‘Empty’ Space Challenges a Tranquil Picture of the Galaxy
Introduction
You might imagine space to be empty. But the seeming void contains a barely perceptible fog of hydrogen and other neutral atoms. In 2020, NASA’s New Horizons spacecraft, having passed the orbit of Pluto, measured a proxy for the amount of hydrogen around it. In the area between stars in our galaxy — the “interstellar medium,” or ISM — New Horizons found around 130 hydrogen atoms per liter of space.
This hydrogen, along with some helium and other molecules, is mostly left over from the Big Bang, and it’s constantly supplemented by infusions from cosmic phenomena such as stars ejecting jets of gas and dust as they are born and shedding their outer layers as they die.
Because the ISM is so diffuse and changes so slowly, astronomers have largely ignored its details for the last half-century, treating it as a stationary backdrop to the flashier happenings of the universe.
But mostly empty space is less simple than it seems.
Over the past few years, astrophysicists have transformed our understanding of the interstellar medium. Using newly developed maps stretching thousands of light-years across our galaxy, they’ve discovered that it’s not the quiet, steady backdrop that researchers thought. Instead, much of the ISM appears to be unstable — a finding that directly contradicts the leading theoretical models taught in textbooks. The surprise finding could help resolve a long-unanswered question about how quickly stars form.
Hot and Cold
In 1969, the researchers George Field, Donald Goldsmith, and Harm Habing came up with a model of how the ISM behaves. They predicted that it exists in two stable states: cold and warm.
As gas and dust float through space, they pull more gas and dust together through gravity, eventually forming a cloud. These clouds tend to cool down, because fast-moving molecules will collide with other molecules and lose energy. Their temperature stays at a bitter 100 kelvins, or about minus 173 degrees Celsius.
But sometimes the gas and dust are too hot to collapse into a cold cloud; instead, they form a diffuse one. A diffuse cloud is much more exposed to nearby stars, which deliver new energy in the form of ultraviolet radiation. This process keeps the cloud at a steady temperature near 8,000 kelvins.
Scientists thought that atoms in the interstellar medium would transition to either the cold or warm state almost instantly, leaving basically no unstable, intermediate ISM behind.
In 1977, Chris McKee and Jeremiah Ostriker added a third phase to the picture: At supernova shock fronts, gas could get even hotter, transforming into a scorching plasma at a temperature of half a million kelvins. Yet even in this expanded framework, the atomic gas outside blast zones was assumed to achieve a calm, pressure-balanced existence.
But it was hard to test the theory. Cold atomic hydrogen emits no visible light. The easiest way to measure it is to look for a rare atomic shift: The electron and proton inside a hydrogen atom will sometimes switch between two possible states. This transition emits a faint radio wave at a wavelength of 21 centimeters.
For more than 70 years, astronomers have pointed radio dishes at the sky to detect these whispers of gas, but looking out along a single line of sight from Earth, they can only collect a tangled pile of signals from overlapping clouds. Sorting through the results is like looking through a stack of semitransparent colored plastic sheets; their colors blend together, making it difficult to identify any individual layer.
Only in recent years, with the launch of new space telescopes, have astronomers been able to probe the space between stars in enough detail to pull these layers apart.
The Gift of Gaia
The Gaia telescope, launched in 2013, created new opportunities to understand the ISM by giving scientists access to a 3D map of the stars around our sun.
You can see one method it used to make this map by holding your thumb in front of your face and closing your left eye, then your right. If you switch back and forth, you’ll notice that your thumb seems to move relative to whatever is behind it. The closer your thumb is to your face, the more your view of it will change. This phenomenon is called parallax.
Gaia observed almost 2 billion stars from different angles as the Earth moved from one side of the sun to the other during its yearly orbit. Studying the effects of parallax allowed researchers to determine the stars’ distances from Earth.
Scientists then studied how the light from those stars dimmed and reddened as it traveled through the ISM on its way to Gaia. By collecting this data from a variety of angles, and by using the distance information they’d gathered through parallax, scientists were able to build up a better understanding of the density of the dust between stars.
But turning that information into a 3D map of the ISM was not straightforward. Many possible configurations of the ISM could satisfy the same data, said Gregory Green, an astronomer at Westlake University in Hangzhou, China. More data offered the astronomers better constraints, but it also complicated their calculations. The challenge, Green said, is picking out the most physically plausible arrangement when the underlying math “becomes impossible.”
Over the last decade, Green and other researchers built advanced statistical frameworks to tackle the calculation. In 2024, a separate team used these tools to create a continuous three-dimensional map of the density of the ISM’s dust inside a sphere more than 4,000 light-years wide around our sun.
The dust map showed researchers where interstellar dust was concentrated, revealing the dense clouds scattered through the space between stars. But it couldn’t tell them how hot or cold that dust was. To understand the full range of ISM temperatures, researchers would need a second map to reveal how it gets heated. That map would come from an unlikely source.
State of Flux
Jonathan Shelest, an undergraduate at the Technion in Haifa, Israel, remembers an astrophysics research seminar in 2024, when Shmuel Bialy, his professor, showed the students images of the gas and dust that gather into billowing structures such as the Pillars of Creation in the voids between stars. “I like to imagine the geometry of everything,” Shelest said. “It was only natural to start imagining all the dynamics, all the structure, all the beauty, and the richness.”
Right after the lecture, Shelest emailed Bialy, asking to join his research group. In an act of kismet, Bialy had recently been looking for a student to explore the ISM through three-dimensional mapping, and so a research partnership was born.
Shelest already had the map of the ISM’s dust. The plan was to combine that map with a map of the ultraviolet radiation that heats the ISM up.
By chance, Bialy located just such a map by striking up a conversation at a conference with the astrophysicist Troy Porter of Stanford University, who had made a map but had yet to publish it.
So Shelest, Bialy, and their colleagues set out to combine the 200 gigabytes of data in the two maps. At every point in space, they compared the density of the dust with the intensity of the radiation to understand where the ISM was hot and where it was cool. Eventually, they were able to combine the dust and radiation information on a three-dimensional grid.
Shelest then set out to see what the map could tell him. The biggest surprise came when he investigated the ISM’s overall temperature: Shelest found that 27% of the ISM in our galactic neighborhood was cold, 32% was warm, and the remaining 41% sat squarely in the forbidden zone as unstable medium. “I thought I was wrong,” Shelest said. “How do you go to your science adviser and tell him that you get so much unstable media?”
But the map didn’t appear to be broken. Shelest saw no evidence of artifacts or random statistical noise in the 3D grid. Instead, the unstable ISM formed massive, coherent blankets that wrapped around the cold clouds completely.
All that midrange medium, neither hot nor cold, implies that the older theory is incomplete, said Adam Ginsburg, an astronomer at the University of Florida. “Something is taking material that should, by the static theory, be sitting in one of these other two states, and it’s stirring it up so that it’s being forced to change states.”
Desika Narayanan, an astrophysicist at the University of Florida, uses an organic metaphor. “Just like your blood in your body is going to have metabolic waste or oxygen in it, and it’s moving different things to different places,” he said, “the ISM is doing the same thing, but with energy, and it’s constantly in a state of flux.”
A Measured Approach
On the July day in 2026 that the group posted the paper, Shelest’s inbox filled with messages from excited astronomers and requests to collaborate. Still, researchers urge caution before we rewrite the textbooks.
The model could have overestimated the amount of unstable ISM if cold and warm sections were too close together for the model to tell them apart, McKee said. Alternatively, the method the team used to calculate the overall distribution of gas and dust could have led them astray, said Philipp Frank, an astrophysicist at the Kavli Institute for Particle Astrophysics and Cosmology at Stanford. The researchers used an “ensemble-averaged mean,” a calculation that naturally tends to smooth over sharp contrasts. If a cold cloud transitioned abruptly to a warm one, this method would artificially soften its steep drop in density into a more gradual slope, which would inflate the amount of unstable ISM.
Shelest and Bialy — whose analysis is currently undergoing peer review — acknowledge that limited resolution and map smoothing are both issues, but they argue that mathematical blurring alone cannot account for the majority of the unstable ISM. When the authors tested their modeling on an entirely different dust map with lower resolution, the unstable fraction shifted by only about 5%, they said.
The Churn of Creation
Galaxies are remarkably inefficient at taking raw material — gas and dust — and turning it into stars. For decades, simulations have struggled to explain why. The new map suggests an answer: Star formation is suppressed by the constant cycle of heating and cooling that churns the ISM.
“The reason why star formation is very inefficient is that feedback heats up and pushes on the surrounding gas,” said Anna Rosen, an astrophysicist at San Diego State University. That churning could explain why classic models, which assume that the ISM is in a tranquil equilibrium, don’t quite seem to match reality. Rosen said the models give us “physically grounded snapshots” — unchanging images of patches of hot and cold ISM — “but in between those snapshots, there’s still a lot going on.”