365daysDate: June 8, 2009

Title: The Universe in Ultraviolet!


Podcaster: Erika Hamden from Columbia Astronomy

Organization: Columbia University Astronomy

Description: Looking at different wavelengths of light can yield new information about the universe around us. By observing ultraviolet radiation, astronomers find regions of recent star formation, as well as stars in the end stages of their lives. I will discuss some of the science gained from observations in this regime, why it has traditionally been difficult to observe in the UV, and how recent technology has allowed us to probe this interesting part of the electromagnetic spectrum.

Bio: Erika is a 2nd-year graduate student in Astronomy at Columbia
University. Her research interests lie primarily in UV instrumentation, local group dynamics, and patterns in nature. Aside from astronomy Erika is a trained chef, and enjoys cooking and eating out in New York.

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Erika: Hello everyone and welcome to Columbia Mondays! My name is Erika Hamden. I’m a second year graduate student at Columbia University. I’m getting a PhD in Astronomy. I’m pleased to be speaking to all you listeners out there today. I’m joined by my friend and colleague Josh, also from Columbia, who will be chiming in with helpful questions.

Josh: Hello there!

Erika: As you probably already know from listening to these podcasts over the past months, astronomy is a huge field which covers some pretty diverse topics – finding planets, studying galaxies, observing stars like our sun, even delving into the history of the universe itself. The methods of discovery are different for each of these different sub-fields. But today what I want to talk about is the field of Ultra-Violet astronomy. We’ll discuss how it differs from optical astronomy, how much harder it is to observe in, and how it can be useful for all those subfields that I mentioned before, as well as lots of others. For reference, I’ll be abbreviating that as “UV” for the rest of the talk.

Josh: Wait, before we go on, let’s talk about what you mean by ultraviolet.

Erika: Good point! So, we are all familiar with optical light – that’s the light which our eyes can see. That’s why it’s called optical. All light travels at the same speed- the speed of light…

Josh: or six hundred seventy billion miles per hour.

Erika: Yes, that’s right. But in addition to having a speed, all light has a wavelength. For really high energy light, like x-rays for example, this wavelength is a tiny length- like 1 nanometer. But for low energy light like radio waves, the wavelength is much much bigger, from centimeters all the way to thousands of kilometers.

Josh: But based on it’s name alone, we know that UV is light that people can’t see. That’s what ultraviolet means: beyond violet.

Erika: UV light has a range from about 100 nanometers to 350 nanometers. Optical light is about 350 to 800 nanometers. So UV is less energetic than x-rays, for example, but more energetic than infrared or optical light and certainly more energetic than radio. UV is the kind of light that gives you a sunburn. Incidentally, bees can see in some parts of the near UV, in order to find flowers.

Josh: By the way, near UV means the light has a wavelength close to optical wavelengths, hence the “near.”

Erika: But UV light is very interesting even if you aren’t a bee. From an astronomical standpoint it can provide lots of information. Very young, newly born, hot stars emit most of their light at UV wavelengths. If you have a UV telescope, you can pick out these new stars much more easily than with an optical telescope. Sometimes with an optical telescope, you can’t see them at all!

Josh: And not just new stars, but old stars, will show up with a UV telescope. What about a cataclysmic variable, for example?

Erika: Well, stars called “Cataclysmic Variables” are usually very bright in UV. Like the name suggests, these stars tend to vary…

Josh: Which means they brighten and then dim.

Erika: and they do this periodically, usually because of some type of explosion. Sometimes the explosion takes place on the surface of the star, and the star will brighten and then dim in a regular way. Sometimes the explosion is so forceful, or it happens in the interior of the star, that it will destroy the star completely. In both of these instances, huge amounts of UV light are emitted. You can think of UV as a good tracer of when things in a star are changing- at birth or at death- lots of UV is a signal that some big adjustments in the structure of the star are happening.

Josh: And even more interesting than individual stars is looking at collections of them! Galaxies look quite different in UV.

Erika: It’s true. Looking at UV light from whole galaxies, not just the stars in them, can provide a lot of information. First, and maybe most obviously, it indicates the amount of star formation going on in a galaxy. Galaxies with lots of clumpy UV emission are places where lots of new stars are being born. Sometimes galaxies which are in the middle of mergers (when two big galaxies collide) exhibit this characteristic: places where gas from the two galaxies has interacted will quickly start to make stars. Sometimes Galaxies which in optical look pretty simple can turn out to be quite different in a UV image.

Josh: But before we run out of time, let’s not forget that you can’t observe anything in the UV unless you have a telescope. And regular telescopes won’t really cut it.

Erika: Regular optical telescopes won’t work at all for the UV. First of all, and most importantly, the atmosphere absorbs a lot of UV light- which is why we don’t have sunburns all the time! In order to even see anything in the first place, you need a space based or weather balloon borne telescope. Both of those won’t be blocked by the Earth’s protective atmosphere.

Josh: And those things don’t come cheap either. Space telescopes cost quite a lot. The Hubble Space Telescope has cost about five billion dollars over it’s lifetime. It’s contributed immeasurably to science and our understanding of the universe, but it’s expensive. That’s why astronomers don’t only use Space telescopes.

Erika: Right! But lets say you have the means to put your telescope into space. You are extremely well funded and you’re pretty lucky! You can’t use just a regular telescope, put it in space, and stick a UV filter on it, the way you might just use a regular telescope with a red filter to look at things in the optical. A lot of the components of normal telescopes are really bad for observing in the UV.

Josh: You’d probably not be very well funded for long if you sent up a telescope that didn’t work!

Erika: Yeah, that would be pretty bad. But the reasons why it would be pretty bad are interesting. A normal optical mirror or optical lenses or even optical camera detectors will absorb the UV photons that you want to observe. So instead of having a mirror that bounces the light back, the light just disappears! To get around this, a telescope maker has to coat a mirror with other materials to make sure that UV light bounces back. In the same way, the camera detector has to be altered to keep the silicon from absorbing all of the light. It’s a pretty difficult field, but in recent years better techniques have been developed to handle all these problems. In the end, the better equipment you have, the better the science is that comes out of it.

Josh: So what’s the state of the art UV telescope? Where is all this great new information coming from?

Erika : Well, one of the best tools for UV observation is the space telescope GALEX. Its mission is to observe galaxies at all stages of evolution and determine star formations rates based on the amount of UV light. Getting back to those galaxies we had mentioned before, some startling images have come back from GALEX- including lots of UV emission from galaxies which were thought to be “dead”.

Josh: And by “dead”, you mean galaxies which, in the optical, look like no new stars have been born in quite a while.

Erika: And even in the UV, most galaxies which are boring in the optical are also boring. But GALEX has found that some of these “dead” galaxies are anything but! There are new stars being born on the outskirts, probably from new gas that is flowing into the galaxy from space. UV light is also a good tracer of this intergalactic material.

Person 2: So it sounds like the field of UV astronomy is pretty exciting. New telescopes and better materials have certainly helped science.

Erika: Yep! And there are more UV telescopes and experiments planned for the coming years, so you can expect this field of astronomy to become even more useful in the future. And also, the images look pretty nice. So, thanks everyone for listening, I hope you enjoyed a little glimpse into the world of UV astronomy. And thanks Josh, for helping me out today!

Person 2: You’re welcome!!

Erika: This has been a podcast from Columbia University, here in the City of New York. Out next Columbia Monday podcast will be by my friend here today, Josh Schroeder. It’s broadcasting on Wednesday June 17th, the topic will be “The Big Bang”. For more info on the public events of Columbia Astronomy, visit our website- Have a great day and keep listening!

End of podcast:

365 Days of Astronomy
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