By Robert Frost, Guest Columnist
This is one of the most famous pictures taken by the Hubble Space Telescope. The features shown in it are called the Pillars of Creation.
These gaseous structures are part of the Eagle Nebula. The Eagle Nebula is 7000 light years away. The picture was taken by Hubble in 1995. The Pillars of Creation are believed to have been destroyed by the blast wave of a nearby supernova, 6000 years ago.
We took a picture of something that was destroyed 6000 years before we took the picture.
That was possible because photography is passive. We don’t send any type of wave or signal or beam towards the object we want to image. It isn’t like radar where a radio wave is sent out, hits an object and bounces back towards us. All we have to do with photography (or more precisely spectrography in this case) is open up our sensor and wait for photons to hit it.
The photons that we detected and allowed us to capture the image of the Pillars of Creation left the gaseous structure 7000 years ago. They were already well on their way towards us a thousand years later when the structure was destroyed.
The same idea applies to the detection of exoplanets such as HIP 116454b. We detect many of these exoplanets by observing changes in the light we are receiving from a star as the planet passes in front of the star. That light left the star HIP 116454b orbits 180 years ago and finally just reached our camera sensors. Those photons were coming towards us regardless of whether or not we wanted to capture them as a photograph.
Because all we are doing when we capture an image is capturing photons that traveled from the imaged object to us, we can take pictures of things that are incredibly far away. In 2011, the Hubble Space Telescope and the Spitzer Space Telescope both captured pictures of a galaxy so far away that it took the photons 13.3 billion years to reach us. This is a galaxy so old it existed just 400 million years after the Big Bang.