Exploring the Hidden Infrared Universe

The bright star at the center of the nebula is Eta Carinae, one of the most massive stars in the galaxy. Its blinding glare is sculpting and destroying the surrounding nebula. Spitzer Space Telescope

To Do Astronomy, Astronomers Need Light

Most people learn astronomy by looking at things that give off light they can see. That includes stars, planets, nebulae, and galaxies. The light we SEE is called "visible" light (since it is visible to our eyes). Astronomers usually refer to it as "optical" wavelengths of light.

Beyond the Visible

There are, of course, other wavelengths of light besides visible light. To get a complete view of an object or event in the universe, astronomers want to detect as many different kinds of light as possible. Today there are branches of astronomy known best for the light they study: gamma-ray, x-ray, radio, microwave, ultraviolet, and infrared. 

Diving into the Infrared Universe

Infrared light is radiation given off by things that are warm. It is sometimes called "heat energy". Everything in the universe radiates at least some portion of its light in the infrared — from chilly comets and icy moons to clouds of gas and dust in the galaxies. Most infrared light from objects in space is absorbed by Earth's atmosphere, so astronomers are used to putting infrared detectors in space. Two of the best-known recent infrared observatories are the Herschel observatory and the Spitzer Space Telescope. Hubble Space Telescope has infrared-sensitive instruments and cameras, as well. Some high-altitude observatories such as Gemini Observatory and the European Southern Observatory can be equipped with infrared detectors; this is because they are above much of Earth's atmosphere and can capture some infrared light from distant celestial objects.

What's Out there Giving Off Infrared Light?

Infrared astronomy helps observers peer into regions of space that would be invisible to us at visible (or other) wavelengths. For example, clouds of gas and dust where stars are born are very opaque (very thick and tough to see into). These would be places like the Orion Nebula where stars are being born even as we read this. They also exist in places like the Horsehead Nebula. The stars inside (or near) these clouds heat the up their surroundings, and infrared detectors can "see" those stars. In other words, the infrared radiation they give off travels through the clouds and our detectors can thus "see into" places of starbirth. 

What other objects are visible in the infrared? Exoplanets (worlds around other stars), brown dwarfs (objects too hot to be planets but too cool to be stars), dust disks around distant stars and planets, heated disks around black holes, and many other objects are visible in infrared wavelengths of light. By studying their infrared "signals", astronomers can deduce a great deal of information about the objects emitting them, including their temperatures, velocities, and chemical compositions. 

Infrared Exploration of a Turbulent and Troubled Nebula

As an example of the power of infrared astronomy, consider the Eta Carina nebula. It's shown here in an infrared view from the Spitzer Space Telescope. The star at the heart of the nebula is called Eta Carinae—a massively supergiant star that will eventually blow up as a supernova. It is tremendously hot, and about 100 times the mass of the Sun. It washes its surrounding area of space with immense amounts of radiation, which sets nearby clouds of gas and dust to glowing in the infrared. The strongest radiation, the ultraviolet (UV), is actually tearing the clouds of gas and dust apart in a process called "photodissociation". The result is a sculptured cavern in the cloud, and the loss of material to make new stars. In this image, the cavern is glowing in the infrared, which allows us to see the details of the clouds that are left. 

These are just a few of the objects and events in the universe that can be explored with infrared-sensitive instruments, giving us new insights into the ongoing evolution of our cosmos.