The universe is illuminated by emissions from distant objects. We see the stars, planets, nebulae, and galaxies in visible light. That’s only a tiny part of all the light that streams from objects in the cosmos across a range called the electromagnetic spectrum. Some emissions, such as ultraviolet, x-ray, gamma ray, and infrared, are absorbed by our planet’s atmosphere, making observations from the ground very difficult. This is particularly true for infrared light, also known as IR. Some IR makes it to the ground and can be detected using specialized instruments at high altitude observatories, but much of it can’t be detected here. To detect infrared light astronomers send specialized observatories into space, such as the Spitzer Space Telescope, launched by NASA in 2003 and still active today.
Infrared light was first detected by Sir Frederick William Herschel in 1800. He was experimenting with filters that would let him look at sunspots when he tried to pass sunlight through a red filter. To his surprise, he detected heat. He called this radiation “califoric rays,” and in time they were referred to as infrared. This light can pass through thick clouds of gas and dust, revealing warm objects inside.
There are three types of infrared that astronomy investigates:
The Spitzer Space Telescope was built with sensitivity to near-, mid-, and some far-infrared light. Its primary mission ended when it ran out of liquid helium to keep the telescope’s instruments at their coldest. However, Spitzer continues to gather data with instruments that do not need such high levels of cooling, and the Spitzer Warm Mission will continue.
The Spitzer Space Telescope has been wildly successful. In 2005 it was the first telescope to directly detect light from two exoplanets orbiting distant stars. The data indicated that these stars were so-called “hot Jupiters” with temperatures of 727°C (1,340°F). Elsewhere, Spitzer may have detected the heat of a collision between two distant planets circling a young star. This could mirror similar collisions that occurred early in the history of our own solar system. In one of its most fascinating observations, Spitzer captured light from what could be the oldest stars in the universe.
Star birth takes place hidden from our view behind thick clouds of gas and dust. Infrared-enabled telescopes such as Spitzer take advantage of infrared light’s ability to pass through dust clouds to reveal the embryos of future stars. In many cases, these stellar seedlings are smothered in huge, pillar-shaped formations that are created when strong radiation from their older, more massive stellar siblings carves away and destroys the star birth clouds. Where optical telescopes would see only a pillar of darkness outlined in starlight, Spitzer lifts the dusty curtain hiding the process of star birth and reveals the stellar newborns.