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Interferometry: Sizing Up the Stars

Video transcript
The video is 6 minutes and 30 seconds long.
Produced by the American Museum of Natural History, September 2006.

Video begins here.

Visual: The Sun shines on Earth in space.

Speaker: Theo ten Brummelaar, Associate Director, Center for High Angular Resolution Astronomy

It’s very difficult to wonder about life, our lives, life on this planet, and life on other planets, without first wondering about stars.

Visual: Theo ten Brummelaar in office

Stars are the substance, the engines that build everything in our known universe. And without understanding stars, we will never understand where planets come from and where we came from.

Visual: The sun rises over a hilltop.  Clouds race by.

Speaker: Gerard van Belle, Research Scientist, Michelson Science Center

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.

Visual: Montage of footage of the solar flares and prominences, a starfield.

You can actually take pictures of it and be able to see sunspots and see solar explosions. And the Sun is the only star that we’ve been able to look at in this sort of detail.

Visual: Gerard van Belle in office.

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.

Visual: An domed observatory on a wooded mountaintop.  Mist swirls by.  
Title: Interferometry: Sizing Up the Stars

Visual: Scientists sit among complex technical apparatus. 

Speaker: Harold McAlister, Director, Center for High Angular Resolution Astronomy

Visual: Harold McAlister in his office CHARA stands for Center for High Angular Resolution Astronomy, which basically is the theme of what we do.

Visual: The camera zooms in on Harold McAlister, creating a heavily pixilated image.

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.

Visual: An domed telescope tower rotates in the night.

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.

Visual: Montage of telescope images of star cluster NGC 4755 in the constellation Crux, star cluster M37 in the constellation Auriga.

Visual: Harold McAlister in his office.

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.

Visual: The CHARA array of telescopes on the hilltop, surrounded by white mist and clouds.

So we get around this problem by synthesizing a single giant telescope with arrays of smaller telescopes.

Visual: Montage of the various telescopes comprising CHARA.  Optical devices in the telescope move into place. 

Visual: Aerial photograph of the entire CHARA array on the mountaintop.  Blue circles highlight the position of each of the six telescopes.

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.

Visual: Long metal pipes housing relay optics, running among the trees, connect each of the telescopes.

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.

Visual: Optical apparatus comprised of mirrors and long, sliding metal tracks.

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.

Visual:  Theo ten Brummelaar uses laptop beside optical apparatus.  Lasers hit a variety of mirrors.

Speaker: Theo ten Brummelaar

This is part of the daily alignment check. Essentially we send a laser beam backwards through the system and check that it hits all the points that it needs to hit. One of the targets is right here.

Visual: A red laser light appears in the center of a target.

Spot on.

Visual: Montage of the CHARA telescopes at night, optical apparatus, and Theo ten Brummelaar at a set of computer monitors.

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.

Visual: Montage of the CHARA telescopes in the woods.

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.

So we have to continuously adjust these paths within the instrument using a thing called a delay line.

Visual: Theo ten Brummelaar standing among tracks of sliding optical apparatus.

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. 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. And that’s what this long tunnel is for. These carts are optical trombones. 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.

Visual: Theo ten Brummelaar at array of computer monitors.  Montage of CHARA telescopes on the mountain.

Speaker: Gerard van Belle

The ability to make images with interferometry is dependent upon how many telescopes you can put into the mix. 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.

Visual: Gerard van Belle in his office.

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.

Visual:  Theo ten Brummelaar examines graphed data on computer monitor.

But if you do enough of it, you can actually get data that you can’t get anywhere else.

Visual: Harold McAlister in office.

Speaker: Harold McAlister

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.

Visual: Computer depiction of star SS 43, image of Regulus based on CHARA data, depiction of Algol binary RY Per, animation of the rapid rotating star Altair

And so we produce images that are based on theoretical models that incorporate the observations, the measurements that we make. 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. And these stars are spinning so rapidly that the centripetal acceleration makes them bloat out at their equator and flatten in at the poles.

Visual: Harold McAlister in his office

All of these stars that we look at would just be points of light without interferometry.

Visual: Image of Delphinus, Sagitta, and Altair, Wolf-Rayet star WR 98A

Speaker: Theo ten Brummelaar

We are able to see detail that no one has been able to see before. Throughout history people have been building new telescopes and discovering things they weren’t expecting to find.

Visual: Theo ten Brummelaar in his office.

The kind of measurements that we can do will, for the first time, really test the models that we have of stars.

Visual: Dusty Nebula around the supergiant V838 Monocerotis

How stars work, how they are born, how they live, and how they die. How planetary systems might or might not form.

Visual: Cepheus A (East) cloud, Galaxy UGC 3294, Galaxy M51, Star-birth field with Taurus

And ultimately about whether life will form upon these systems. And since our understanding at the moment is that we came from the stars, well, that’s where we have to go to find out about things.


Video ends here.