As someone who fields a lot of questions about the James Webb Space Telescope, a giant infrared observatory being built right now, I see a lot of “Why infrared?” questions.
There are a lot of answers to this, but here’s one I think is particularly interesting and illustrative of why infrared light is a valuable tool for understanding the universe. And that is – without the use of infrared telescopes it’s really, really hard to see stars being born.
Stars are born inside thick clouds of dust. These clouds, or nebulae, are actually quite pretty. Here’s a really famous image of a beautiful nebula taken by the Hubble Space Telescope that you may recognize:
Pillars of Creation, Credit: NASA, Jeff Hester, and Paul Scowen (Arizona State University)
While this image is spectacular, the problem is – there are stars inside those pillars of dust that Hubble can’t see. And that’s because the visible light being given up by those stars is being obscured by the dust. BUT, what if we used a telescope sensitive to infrared light to look at this nebula?
Here’s Herschel’s far-infrared view:
Credit: ESA/Herschel/PACS/SPIRE/Hill, Motte, HOBYS Key Programme Consortium
And here is a comparison of the Hubble image with one taken by NASA Spitzer:
Credit: NASA/JPL-Caltech/Institut d’Astrophysique Spatiale
Both infrared views reveal more structure to the dust clouds and hidden stars are revealed. The existing infrared images of the Pillars of Creation are slightly lower res than the visible light Hubble image (maybe the James Webb Space Telescope will get a nice hi-res infrared view?), so how about the “Mystic Mountains” of the Carina Nebula? Hubble has a little bit of infrared capability, so compare these two images, one in infrared and one in visible light:
Credit:NASA/ESA/M. Livio & Hubble 20th Anniversary Team (STScI)
Quite a difference – and lots more stars are visible that weren’t before.
So how does this work? Well, let’s try this little thought experiment. What if you were to put your arm into a garbage bag?
Your arm is hidden. Invisible.
BUT, what if you looked at your arm and the garbage bag with an infrared camera? Remember that infrared light is essentially heat. And that while your eyes may not be able to pick up the warmth of your arm underneath the cooler plastic of the bag, an infrared camera can. An infrared camera can see right through the bag!
And this is how the infrared telescope works as well. It sees the heat or infrared light being emitted by the stars within the cooler dust clouds.
Here’s one more famous comparison for you. The gorgeous Horsehead Nebula:
And the recently released Hubble image showing the Horsehead in infrared light:
Credit: NASA/Space Telescope Science Institute (STScI)
So, that’s why infrared! And just one reason why a super powerful infrared observatory (like JWST) will be able reveal more of the hidden secrets of the places where stars are born.