當(dāng)你凝視夜空時(shí),你可以在沒(méi)有望遠(yuǎn)鏡的情況下看到成千上萬(wàn)的星星。[HW:我們就別想了]這可能聽(tīng)起來(lái)很多,但那些實(shí)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(shù)的。那是因?yàn)槲覀兊男窍挡粌H充滿(mǎn)了星星,還有塵埃和氣體阻擋了我們對(duì)昏暗或遙遠(yuǎn)星星的視線(xiàn),所以天文學(xué)家必須反著來(lái)回答這個(gè)問(wèn)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(gè)星系中有多少物質(zhì)或質(zhì)量。亞利桑那大學(xué)的天文學(xué)家最近估計(jì),銀河系的質(zhì)量約為我們太陽(yáng)的9600億倍。它由星星、塵埃、氣體……和暗物質(zhì)組成。暗物質(zhì)是神秘的,科學(xué)家們并不確定它是什么。然而,他們可以看到暗物質(zhì)的重力在繞星系中心運(yùn)行時(shí)如何影響恒星。“基本上恒星移動(dòng)得越快,暗物質(zhì)就越多,”圖森市亞利桑那大學(xué)天文系教學(xué)專(zhuān)家馬蘭卡·里博金解釋說(shuō)。據(jù)信暗物質(zhì)占星系中約90%的物質(zhì)。一旦減去暗物質(zhì)和塵埃和氣體,就會(huì)得到所有的星星 - 相當(dāng)于大約30到500億個(gè)太陽(yáng)。
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(shí)際的恒星數(shù)量遠(yuǎn)遠(yuǎn)高于此數(shù)。因?yàn)楹阈强梢允俏覀冏约禾?yáng)質(zhì)量的8%到20倍之多。當(dāng)天文學(xué)家觀(guān)察恒星誕生的地方時(shí),他們看到的小恒星遠(yuǎn)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?chē)×硕嗌俸阈?。而且我們大致知道那些質(zhì)量應(yīng)該多少大恒星和多少小恒星,這就意味著我們應(yīng)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(jì)算銀河系恒星的每一步都有很多猜測(cè)。這意味著,對(duì)于銀河系中有多少顆恒星,只是有一個(gè)估計(jì)值。根據(jù)你問(wèn)的對(duì)象,我們銀河系可能有2千億到1萬(wàn)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(guān)的數(shù)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(shuō):“當(dāng)你抬頭仰望夜空,意識(shí)到那里有數(shù)千萬(wàn)億顆恒星,以及這個(gè)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(kāi)始了解宇宙的規(guī)模了。”