W4 Part 1 - Catching the Light from the Stars

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En provenance du cours de The University of Edinburgh

AstroTech: The Science and Technology behind Astronomical Discovery

223 notes

The University of Edinburgh

AstroTech: The Science and Technology behind Astronomical Discovery

223 notes

"How do they know that?" Modern astronomy has made some astonishing discoveries - how stars burn and how black holes form; galaxies from the edge of the universe and killer rocks right next door; where the elements come from and how the expanding universe is accelerating. But how do we know all that? The truth is that astronomy would be impossible without technology, and every advance in astronomy is really an advance in technology. But the technology by itself is not enough. We have to apply it critically with a knowledge of physics to unlock the secrets of the Universe. Each week we will cover a different aspect of Astronomical technology, matching each piece of technology to a highlight science result. We will explain how the technology works, how it has allowed us to collect astronomical data, and, with some basic physics, how we interpret the data to make scientific discoveries. The class will consist of video lectures, weekly quizzes, and discussion forums. Each week there will be five videos, totalling approximately 40 minutes. They will be in a regular pattern - a short introduction, an example science story, an explanation of the key technology area, a look at how the technology is used in practice, and finally a look at what the future may hold.

À partir de la leçon

Detectors and the First Galaxies

Detectors, how they work, and how we use them to catch the light from the very first galaxies.

W4 Part 1 - Catching the Light from the Stars5:01

W4 Part 2 - Galaxies since the Dawn of Time4:24

W4 Part 3a - Light, Matter, and CCDs15:01

W4 Part 3b - Infrared Detectors5:36

W4 Part 4 - Galaxies since the Dawn of Time Part II7:03

W4 Part 5 - Another Revolution in Detector Technology? 1:57

Rencontrer les enseignants

Andy Lawrence

Physics and Astronomy
Catherine Heymans

Physics and Astronomy

So, we've built a telescope to catch the light coming down from the sky.

If necessary we've gone above the atmosphere to

catch the kind of light that we want to.

But now what we have to do is to record

the information that we're seeing, using some kind of detector.

Now the detector does four things for us.

Firstly, it makes an objective record of what it is that we're seeing.

The second thing is that it allows us to digitize the information.

Pretty pictures are all very nice, but as scientists, we want numbers.

The third thing is that it allows us to integrate, that is to take long exposures,

to gradually add up more and more light so we can see fainter and fainter objects.

The final thing is perhaps the most

important. With detectors of various kinds, we can

detect kinds of lights that we cannot see

with our eyes, infrared, x-rays, radio, et cetera.

And so, we discover things about the

universe we otherwise would not know existed.

Let me show you some examples.

So, this first example is a giant radio galaxy.

It's the radio galaxy, Hercules A.

So in the image you're looking at the purple color is a map of

the radio emission as measured with the Very Large Array in New Mexico.

It's superimposed on a regular visible light

picture so you can see the parent galaxy.

So what you see in that purple emission is two twin jets of radio plasma,

stretching out an enormous distance into space, and we think these have

been squirted out of a black hole in the very center of that galaxy.

So extraordinarily interesting. To see that radio emission, we need an antenna and

a radio receiver otherwise we would never

have known that such extraordinary things existed.

So this next example is one you've seen before.

This is hot gas from the cluster of galaxies Abell 1689.

So in this image you're looking at the purple color in

this case is x-ray emission measured by the Chandra Space Observatory.

And it's superimposed again, on a regular visible light image taken with the

Hubble Space Telescope, where you can see the galaxies, and the cluster of galaxies.

So what the X-ray emission is showing us is smooth emission from very hot gas.

It has to be tens of millions of

degrees, almost 100 million degrees to radiate those X-rays.

So once again, we need a special kind of detector.

We need some substance that detects x-rays, otherwise

we would not have known that gas was there.

As well as being very fascinating, it's

very important because from the temperature and

the brightness of that x-ray gas, we can weigh the dark matter in that cluster,

and it turns out to be 99% of the mass of that cluster.

So this final example is the Hubble Ultra Deep Field,

a very deep picture taken by the Hubble Space Telescope.

This image shows the importance both of

integration and of observing at different wavelengths.

So the faint tiny smudges that are circled in the image you're looking

at are showing you the locations of some of the most distant galaxies we know of.

Now in order to detect those incredibly faint smudges, the Hubble Space

Telescope stared at the same patch of sky, for four days, nonstop -

a total exposure of 173,000 seconds.

It just kept adding up more and

more and more light to see extremely faint things.

So that's how we can see those very, very distant galaxies.

But also, as you'll be hearing later

this week, those distant galaxies are red shifted.

Their light is mostly emitted in the infrared, rather than as visible light.

So to measure that best, we need

infrared detectors, as well as visible light detectors.

So, there you have some science examples,

the kind of science we can do with detectors of various different kinds.

What we want to do this week is to understand how those detectors work.

How do we actually achieve this?

To do that, we need to look at how light interacts with matter,

and then, how we assemble devices into instruments we can actually use.

So that's our task this week. But before we do that

Catherine is going to tell you more about those extremely distant galaxies.

[BLANK_AUDIO]

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