Ep. 132: Infrared Astronomy

Transcript: Infrared Astronomy

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Fraser Cain: Today we continue our unofficial tour through the electromagnetic spectrum stopping at the infrared. We feel it as heat. This section of the spectrum gives us our only clear view through dusty materials to see the newly forming planetary systems and shrouded super massive black holes.

Infrared lets us look out at the most distant regions of the observable universe when the first building blocks of galaxies came together. Pamela, let’s once again sort of follow our path along the electromagnetic spectrum. We did radio, and then we did the submillimeter, stopping at infrared. What is our range of infrared?

Dr. Pamela Gay: Once we start getting infrared we deal with everything that is 750 nanometers on the blue edge which is admittedly as red as you can ever possibly see. Then exactly where it ends depends on exactly who you’re talking to.

We have near, mid, far infrared but in general we start getting to light. As scientists you can start to measure, we’re starting to deal with things that are as long as 350 microns which is starting to get to be the size of a piece of hair basically.

Fraser: Then which is which? Which is near and which is far?

Pamela: Near infrared is the stuff that is closest in wavelength to what we can see with our eyes. In fact there are some snakes – pit vipers, rattlesnakes – that are actually able to perceive things in the near infrared.

Fraser: When I look at one of those infrared video cameras, is that it?

Pamela: That’s all in the infrared.

Fraser: That’s near infrared.

Pamela: Yes.

Fraser: That’s sort of showing the heat coming off the body. So, near is what is closest to the red end of the spectrum and far I guess is the furthest, the longer wavelength is far.

Pamela: As we start talking about near, mid, far infrared we’re actually also talking about the temperatures that we’re looking at. So as we look at things that are near infrared we’re looking at things that are hot but not too hot. Things that are cooler than about 4900 degrees.

Fraser: You’re calling that not too hot? [Laughter] 4900 degrees, 4900 degrees Kelvin, right?

Pamela: Well, it is 5200 degrees Kelvin and about 4900 degrees Celsius rounding liberally. On the scale of stars which is the type of stuff that we deal with in astronomy, yeah, these are in terms of stars fairly cool objects.

When you get to far infrared you’re dealing with just plain really, really cold. To use Kelvin we’re looking at things as cold as ten to twenty degrees Kelvin which we’re looking at way in the negative numbers of Celsius.

Fraser: Right, that’s just a few degrees above absolute zero. That’s quite a temperature range.

Pamela: It is a fairly large wavelength range as well. Visual is a very small wavelength range. Most of the other wavelength ranges we define by where are the holes in the atmosphere.

Infrared is one of those places where it is pretty much defined as on one side you have where does visual light end. But then on the other side we’re starting to look at what are the holes in the atmosphere that allow us to see the infrared.

We have a whole set of holes that fall into those wavelength bands and then once we start getting the microwave it is solid. You can’t see through the atmosphere. That’s how we start looking at defining the infrared is where are the holes in the atmosphere.

Fraser: What does a piece of equipment that is used to detect the infrared look like?

Pamela: It looks like the detector inside your digital cameral actually. This is one of the cool things about infrared as opposed to submillimeter and radio. For near infrared in particular you can detect it with the same detectors that you use for normal optical light.

In fact your standard Canon Rebel, your fancy smansy digital camera actually have infrared blocking filters in them because otherwise all the infrared light gets in and makes people look a kind of funny color. It lets you take light into the twilight a little bit further.

So, if you want to take a lot of low-light photos and you don’t care if the color is a little bit strange you can actually tear apart your camera – and there is instructions online on how to do this – and very carefully remove that IR blocking filter and then your camera will happily detect this light.

Fraser: What about focusing? What kind of apparatus is required to actually focus the infrared?

Pamela: It all works exactly like visible light. You’re talking about normal telescope lenses, normal telescope mirrors. Where it starts to get tricky though is you have to worry about temperature. Just like trying to take a visible light picture in a room with way too many floodlights on leads to a completely washed out picture without a lot of details.

In the case of infrared trying to take a picture where you’re looking at the far infrared where you’re very sensitive to temperature you have to cool down all of your equipment or you’re going to be getting blinded by the fact that your telescope tube is hot.

You have to be aware of what is going on in your system, how can you make sure everything is cold. How can you, not essentially turn the floodlights on by letting your room get warm.

Fraser: I guess for near infrared it is not as big of a problem but the far infrared is a huge problem. With near infrared my room is not going to be 3000 Kelvin [Laughter]

Pamela: No this is where you can buy off the shelf near infrared cameras and use them to take weird pictures of your friends. They get used a lot for things like night pictures of random animals for health science reasons where you can look for circulatory disorders using infrared cameras.

When you start getting into the far infrared you have to start cooling your detector with not just liquid nitrogen but often with things like liquid helium as well to get it extremely cold so the warmth of your detector doesn’t distort your images.

Fraser: I think we understand where it sits on the spectrum. We’ve got a pretty good idea of what the apparatus is. It is very familiar. It is something we can all wrap our heads around nice big telescope with a CCD array attached to it. It is very similar to what you see with a regular visible light telescope. So then, what is it for?

Pamela: You can look through dust and that’s just cool.

Fraser: Why can’t we look through dust?

Pamela: In general dust, fog, small particles, well light doesn’t light doesn’t exactly pass through them so well. You have light from a distant object that is trying to pass through a cloud of dust grains, gas, or molecules. Depending on the wavelength of light you have a different probability that a particular photon is going to end up hitting something and getting scattered off at a random angle.

The probability of a random photon of light getting redirected through a scattering process is directly related to what color it is. Really blue light gets scattered very easily. This is where you get blue reflection nebula. Whereas red light is able to pass through clouds and gas readily.

Infrared light passes through even better. If you have a thick enough cloud it will first deflect all the blue light. Then as you grow your cloud it will deflect progressively redder light until finally all the visible light is deflected and not able to make it through the cloud. This is where you get things like globules that appear completely black on the sky.

Then if you instead look at it in the infrared, the infrared light at its longer wavelength is able to make it all the way through the gas and dust. This is a way of peering into the center of our galaxy. It is a way of peering into star forming regions, really thick molecular clouds. It is essentially a way of looking through with superman’s x-ray vision to see what is it that is at the center of our galaxy?

It was used by Andrea Getz to image the stars that are orbiting the super massive black hole at the center of the Milky Way. She actually, using infrared, was able to see them orbit over the passage of a number of years.

Fraser: That’s one of the coolest videos you can watch is these stars whipping around this invisible spot in the sky.

Pamela: If you try looking at the point where the center of the Milky Way is located on the sky with a normal optical telescope you just see pretty clouds of gas and dust and stars, but you can’t see all the way into the center. You’re blocked by the intervening dust.

Using infrared you can see all the way through to the center. This also allows us to get a look in at stellar nurseries. We can peer through the clouds of gas and dust and see the seeds of stars that are going to be blaring out all of that gas and dust in the future but for now are just slowly condensing.

The other nice thing about the infrared is as we look at more and more distant objects in the universe, they’re getting red shifted. What we see as the pretty blue spiral arms of nearby galaxies, that pretty blue color even the most extreme blue light at 380 nanometers, once you get 6 billion light years away or so depending on the cosmology you choose to use that light at the bluest edge of what you’re able to see with your eyes had gotten moved over into the infrared.

Fraser: It is sort of in the same process that is going on with the cosmic microwave background radiation. The wavelengths of that blue light are getting stretched out. It started out blue but now that there has been so much expansion in the universe those photons are now in the red and into the infrared.

Pamela: Yeah, we have this combination process of the objects are getting carried away from us which is causing a Doppler effect and the universe itself is expanding which is also adding an extra expansion turn to the wavelength.

Put together, we basically lose the light from these galaxies into the infrared at the wavelengths that for different science topics are the most interesting.

Fraser: You are saying that is about what 6 to 8 billion light years away?

Pamela: At a red shift of about one is where we start to stop being able to see visible light within any of the visible bands to our eyes.

Fraser: So I guess you point a telescope at one of those, a regular visible light telescope and stuff is just starting to disappear.

Pamela: What you end up seeing is the light that is being given off in the ultraviolet now ends up appearing so everything is getting shifted. If you think about where stars are giving off the majority of their light, a lot of stars are giving off the majority of their light at the wavelengths that the human eye is most sensitive to.

This is where future telescopes and modern telescopes like Spitzer that is currently on orbit and like the future James Webb space telescope are so important. They allow us to look back at earlier moments in the universe and the allow us to peer into these dusty regions to understand things we can’t otherwise see.

Fraser: I think this is one of the big surprises that a lot of people have is the James Webb, which is the next observatory, is going to be a super duper Hubble space telescope.

It is going to have a much bigger mirror, far more sensitive. It is going to be many multiples of capability of what Hubble can do but it’s only infrared.

Pamela: I think that this is one of the perhaps misconceptions that is going around is we have a really good infrared telescope orbiting right now – the Spitzer space telescope. It is nothing like what James Webb is going to be able to do. But Spitzer is doing a great job.

When we talk about James Webb we always talk about it – all of us, we’re all guilty of this at one point or another – as the replacement for Hubble, but it is not. The Hubble space telescope is an extremely versatile telescope. It is able to see into the ultraviolet with one set of instruments and able to see into the infrared with another set of instruments.

It is able to make these amazing visible light images. It is the only thing on orbit doing visible light and doing science with the visible light at such a scale as we’ve gotten with the series of cameras.

James Webb is focused in mission. It is an infrared telescope. It is an amazing giant out in an orbit a space shuttle will never reach. It is an amazing future telescope but it is not a replacement for Hubble. It is its own specific thing with its own narrow wavelength range that it is going to be looking at.

Fraser: I guess that was the theory, right? That was the plan that if you build such a sophisticated instrument you should be able to get to the very edges of the universe, be able to see the stuff that is red shifted way beyond the 6 to 8 billion light years that we’re talking about.

You should be able to see right in and see those planets forming right through the dust to look at the very centers of these super massive black holes and look at these galaxies. It is wonderful that it is going to do this but the days of Hubble are a long way away from being over. There is no true Hubble replacement which is a total shame.

Pamela: Right now we’re recording this, who knows when you’re listening, but we’re recording this in 2009. One of the things the astronomy community does on a regular basis is every ten years we get together as a community and we put together what is called a decadal survey.

It basically covers where have we been for the past ten years and what are the open questions that we need to focus significant effort and funding and resources into answering into fixing and to doing in the next ten years?

What I’m waiting to see is the people who are on the instrumentation working groups, the science goals working groups, do they say astronomy community, NASA listen up we really need to have a replacement for Hubble?

Or do they say we need to invest in massive optical telescopes on the ground, ultraviolet telescopes in space? How do they take the science that can currently only be done by Hubble and divvy it out to future projects?

Fraser: Maybe we will be able to get a replacement for Hubble in the future. We’re not talking about Hubble although Hubble can do infrared, right?

Pamela: Nope but what we’re talking about is what’s the cool stuff that we can get out of infrared.

Fraser: Right, okay so we’ve talked about the generalities about what infrared astronomy is really good for. Now can you give us some specifics? Can you give us some really cool results so far that have only been turned up through infrared?

Pamela: I think my favorite personal result although it may not be the scientifically most amazing result is the Spitzer space telescope has gone through and systematically re-imaged some of the most photogenic things in the nearby universe.

For instance they did this amazing image of the nearby Andromeda Galaxy. They were actually able to figure out that we have seriously underestimated the size of Andromeda. As they looked at it in the infrared they were able to find all the cold dust that is not giving off light in the optical. We just hadn’t realized how much of it was there.

They’ve also gone through and re-imaged this amazing image from Hubble of a section of the Evil nebula that has been named the Pillars of Creation. It is actually featured in one of the Star Trek movies. They went through and re-imaged that with the Spitzer as well.

Now these are what appear in the optical to be completely solid dense pillars of gas. You can start to peer through them. You can start to see the starlight from behind them and the stars inside turning on and lighting up.

Fraser: On a completely side note, sorry to do this to you Pamela, but there was a scientific result I guess about two years ago that someone had calculated that the Pillars of Creation have probably been destroyed by a supernova.

Pamela: Yeah, I loved that result. I was in that press conference and it was just one of these where all of us were going: “Oh.” There is an article about that on starstryder somewhere.

Fraser: It is such a rich region. There are so many likely supernova in that region that any one of them could blow away the dust that has been forming that it is likely that one of the nearby supernova have destroyed the pillars.

So, what we see is not what is really there anymore. Wrap your head around that because it is like 5,000 light years away or however far away it is.

Pamela: There is a specific instance of they knew this supernova had gone off this year and if you take the difference between how long ago the light is that we saw and when the supernova went off, the supernova has already destroyed everything. We just haven’t had a chance to see it yet. It was one of those kind of everything is temporary moments.

Fraser: Okay, so more cool results.

Pamela: This is literally cool results because we’re looking at cool light.

Fraser: Ooh, zing. [Laughter]

Pamela: Then there is also all the results with extrasolar planets where Spitzer has actually been able to see some of these hot Jupiters. Their orbits allow them to be spatially resolved away from the parent star when we start looking at them in the infrared.

There are just all these really cool results of we’re seeing a new view on galaxies, on star formation, and on planets around other stars which is just completely new science.

Fraser: With the Spitzer view they’re actually seeing weather. Not weather systems but they’re seeing how fast winds are moving across the surface of these planets orbiting other stars. I think that it was about a year ago Spitzer made the first independent view of a planet.

Pamela: Right.

Fraser: It actually took a picture of a planet orbiting a star. Which you’d think with all the planets that have been discovered, that would have happened a long time ago.

The reality is they’ve only been detected by the way they affect the parent star. But for the first time an independent photograph of a planet was taken which is just astonishing. Go Spitzer!

Pamela: Spitzer is just the first of the truly great infrared observatories. Once we get James Webb in orbit the great hope we all have for James Webb is it is going to start to make the earliest galaxies that formed in our universe more than not well developed red blobs in images.

They’re still going to look like red blobs because that’s what we think they morphologically are is blobs of gas and stars that haven’t had a chance to form nice pretty grand design spirals or anything like that yet.

It will be the difference between taking a picture where you don’t have enough light and you can tell there’s a tree in the picture but that’s all you know is, yeah I think that’s a tree and being able to see every leaf, all the details and go, oh that’s a Cypress.

With the James Webb space telescope we’ll also be able to see things that are too faint to be seen right now. We’ll be able to start to understand what was the population of galaxies when the universe was a couple billion years old, 3 or 4 billion years old in a richness that we can’t see right now.

Right now we can only really see the brightest galaxies in the earliest moments of the universe. We’ll start to be able to see all the little spuds out there that are working toward forming giant galaxies.

Fraser: James Webb is going to launch when?

Pamela: This is a NASA project and I love NASA but they have a tendency to move launch dates.

Fraser: They don’t even have an administrator right now.

Pamela: Well yeah, it’s a bit problematic. Anyway, NASA, the European Space Agency, the Canadian Space Agency, they’re all working together toward hopefully a June 2013 launch date.

Right now the way it is being phrased it is “no earlier than June 2013.” Once it is launched the goal is it will keep going for ten years but the engineers are promising five.

Fraser: So, expect forty. [Laughter]

Pamela: Well if it works sort of like the Mars exploration rovers.

Fraser: Exactly. I guess with that once again we’ll probably have the coolant. The coolant is going to run out so they’ll only have a certain amount of really cold observing time and then we’ll move to a warm period.

Pamela: That’s something that I think we missed mentioning. With all of these systems you have to keep them cold. Spitzer is going to eventually run out of coolant. Here’s the thing, James Webb isn’t actually employing huge amounts of coolant. It is sort of going “okay as long as I’m in the shade, I’m fine.”

Space itself is really cold so we’re sticking the James Webb telescope out in the Lagrange point that is on the opposite side of the Earth from the sun.

This is like we talked about a couple of question shows ago. They’re building this really strange sunshield that protects the entire telescope from being illuminated from Earthshine, from sunshine.

By keeping the mirror constantly in the shade – although amusingly enough the artist’s impression shows sunlight hitting the mirror – [Laughter] by keeping the entire system in shade they don’t have to worry about running out of coolant.

It will die eventually but it could live the way the Mars exploration rovers have lived by just sort of getting through and just keep doing their thing forever.

Fraser: Very cool. Thanks Pamela, we’ll talk to you next week.