Science Bulletins: Interferometry—Sizing Up the Stars발음듣기
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Science Bulletins: Interferometry—Sizing Up the Stars
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출처 : 칸아카데미
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It’s very difficult to wonder about life, our lives, life on this planet, and life on other planets, without first wondering about stars.발음듣기
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And without understanding stars, we will never understand where planets come from and where we came from.발음듣기
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We have one star that we’ve been able to study in exquisite detail, and that’s the Sun and that’s because it’s so close by.발음듣기
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And this is where you need special techniques to look at other stars and see them in the sort of detail that has been previously only done for the Sun.발음듣기
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CHARA stands for Center for High Angular Resolution Astronomy, which basically is the theme of what we do.발음듣기
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Resolution is the ability to see fine detail in distant objects, and unfortunately, distances are so great in astronomy that resolution has always been something that has been unattainable for most of the objects we look at.발음듣기
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Stars, for example, are so far away that even with the biggest telescopes that we've ever built most of them appear just as points of light.발음듣기
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But the kind of problems that we have to solve involving measuring sizes of stars requires us to build telescopes that are not just tens of meters across, but hundreds of meters across, and those are completely unfeasible for the indefinite future.발음듣기
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So we get around this problem by synthesizing a single giant telescope with arrays of smaller telescopes.발음듣기
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The CHARA array is a collection of six telescopes that are arranged on the ground in an area that more or less kind of covers the area that a single large telescope mirror would have.발음듣기
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And what we then have to do is to have relay optics— many, many mirrors along the way to effectively move the beams as if the telescopes were all placed lying on this optical mirror that we’re trying to synthesize.발음듣기
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And that’s been the real problem with interferometry, being able to precisely control the beams of light to attain that synthesis of a single mirror.발음듣기
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Essentially we send a laser beam backwards through the system and check that it hits all the points that it needs to hit.발음듣기
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It's very important that from the star all the way to the point inside the instrument where we bring the light beams together that the light travel time is exactly the same.발음듣기
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Now because the telescopes are at different elevations and different parts of the mountain and the Earth is constantly rotating, these paths are forever changing.발음듣기
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So we have to continuously adjust these paths within the instrument using a thing called a delay line.발음듣기
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In interferometry, timing is everything and that means that we have to get the light from all six telescopes around the mountain into this room at the same time.발음듣기
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While we can’t control the speed of light or the time it travels, what we can do is change the path length over which it travels.발음듣기
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Such that we can add and subtract path-length and make the light from each of the six telescopes arrive at the same time at the back end so that we collect the data to make our pictures.발음듣기
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The ability to make images with interferometry is dependent upon how many telescopes you can put into the mix.발음듣기
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As you add more and more telescopes, you get to fill in more and more pieces of this image that you're trying to synthesize as if you had a big telescope.발음듣기
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So, in the end, you're never going to get all the way there, because you're never going to be able to put a telescope on every piece of the landscape that is pretending to be your overall telescope.발음듣기
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The bread and butter work, if you will, of the array is measuring these fundamental parameters for stars—their sizes, their shapes, masses, distances, luminosities, and things like that.발음듣기
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And so we produce images that are based on theoretical models that incorporate the observations, the measurements that we make.발음듣기
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For example, we have been looking at stars that are rapidly rotating, spinning on their axes, in a matter of hours, rather than, in the case of the Sun, about a month.발음듣기
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And these stars are spinning so rapidly that the centripetal acceleration makes them bloat out at their equator and flatten in at the poles.발음듣기
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Throughout history people have been building new telescopes and discovering things they weren’t expecting to find.발음듣기
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The kind of measurements that we can do will, for the first time, really test the models that we have of stars.발음듣기
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