銀河系有多少星星？

When you gaze up into the night sky, there are thousands of stars you can see without any help from a telescope. That might sound like a lot. But those stars are actually just the ones that are brightest and closest to Earth. The Milky Way—the galaxy Earth calls home—is bigger. A whole lot bigger. But just how many stars are there in the galaxy?

當你凝視夜空時，你可以在沒有望遠鏡的情況下看到成千上萬的星星。[HW：我們就別想了]這可能聽起來很多，但那些實際上只是最亮和最接近地球的恒星，銀河系里可是有一大堆星星呢!但是銀河系中究竟有多少顆恒星呢?

Unfortunately, we can’t simply look at all the stars with telescopes and count them up. That’s because our galaxy isn’t only full of stars. There are also clouds of dust and gas that block our view of dim or faraway stars. So astronomers have to answer this question by working backwards.

很抱歉，我們不能用數的。那是因為我們的星系不僅充滿了星星，還有塵埃和氣體阻擋了我們對昏暗或遙遠星星的視線，所以天文學家必須反著來回答這個問題。

The first step is to figure out how much stuff, or mass, there is in the entire galaxy. Astronomers at the University of Arizona recently estimated that the Milky Way weighs about 960 billion times as much as our own sun. It’s made up of things like stars, dust, gas… and dark matter. Dark matter is mysterious and scientists aren’t really sure what it is. However, they can see how gravity from dark matter affects stars as they orbit the center of the galaxy. “Basically the faster your stars are moving, the more dark matter there is,” explains Malanka Riabokin, an instructional specialist in the astronomy department at the University of Arizona in Tucson. Dark matter is believed to make up around 90 percent of the material in the galaxy. Once you subtract the dark matter and dust and gas, you’re left with all the star stuff—the equivalent of about 30 to 50 billion suns.

第一步是弄清楚整個星系中有多少物質或質量。亞利桑那大學的天文學家最近估計，銀河系的質量約為我們太陽的9600億倍。它由星星、塵埃、氣體……和暗物質組成。暗物質是神秘的，科學家們并不確定它是什么。然而，他們可以看到暗物質的重力在繞星系中心運行時如何影響恒星。“基本上恒星移動得越快，暗物質就越多，”圖森市亞利桑那大學天文系教學專家馬蘭卡·里博金解釋說。據信暗物質占星系中約90%的物質。一旦減去暗物質和塵埃和氣體，就會得到所有的星星 - 相當于大約30到500億個太陽。

But the actual number of stars is much higher than that. That’s because stars can be anywhere from 8 percent the mass of our own sun to 20 times as large. When astronomers look at the places where stars are born, they see tiny stars are much more common than massive ones.

但實際的恒星數量遠遠高于此數。因為恒星可以是我們自己太陽質量的8%到20倍之多。當天文學家觀察恒星誕生的地方時，他們看到的小恒星遠多于大恒星。

So we know how much star stuff is floating around the galaxy. And we know roughly how much of that mass should be big stars, and how much should belong to small stars. That means we should know how many stars there are in total, right?

所以我們知道在銀河系周圍漂浮了多少恒星。而且我們大致知道那些質量應該多少大恒星和多少小恒星，這就意味著我們應該知道了總共有多少顆星星了吧?

Well, kind of. There’s a lot of guesswork that goes into each step of counting the stars in the galaxy. This means that there isn’t just one estimate for how many stars are scattered across the Milky Way. Depending on whom you ask, there may be anywhere between 200 billion and 1 trillion stars out there.

差不多吧。計算銀河系恒星的每一步都有很多猜測。這意味著，對于銀河系中有多少顆恒星，只是有一個估計值。根據你問的對象，我們銀河系可能有2千億到1萬億顆恒星。

Any way you slice it, though, that’s a lot of stars.

但是不管如何區(qū)分，這也是很可觀的數字了。

“When you look up at the night sky and realize that there are literally billions upon billions of stars that you cannot see, and just how deep that space must be to accommodate all those stars (and other galaxies, so much farther away!) it starts to give you an appreciation of the scale of the Universe,” Riabokin says.

里博金說：“當你抬頭仰望夜空，意識到那里有數千萬億顆恒星，以及這個空間必須有多廣袤才能容納所有這些恒星(以及其他星系)，這就讓你開始了解宇宙的規(guī)模了。”