Why an Infrared observatory is key to seeing the first stars?

Why is a potent infrared observatory crucial for seeing the first stars and galaxies that formed in the cosmos? Why on earth do we even want to see the first stars and galaxies that formed? One simple reason is… we haven’t yet! The microwave COBE and WMAP satellites saw the heat signature left by the Big Bang almost 380,000 years after it transpired. But at that point stars and galaxies didn’t exist. Actually the universe was a pretty dark place.

Envisage light leaving the first stars and galaxies approximately 13.6 billion years ago and traveling through space and time to reach our telescopes. We’re in effect seeing these objects as they were when the light first left them 13.6 billion years ago. By the time this light comes to us, its color or wavelength shifts towards the red, something we call a “redshift.” Why? In this specific case, it’s because in case of very distant objects, Einstein’s General Relativity comes into play. It tells us that the expansion of the cosmos means it is the space between objects that in fact stretches, causing objects (galaxies) to move away from each other. Additionally, any light in that space will also stretch, shifting that light’s wavelength to lengthier wavelengths. This can make faraway objects very dim (or invisible) at visible wavelengths of light, because that light comes to us as infrared light.

Redshift means that light that is released by the first stars and galaxies as visible or ultraviolet light, in fact gets shifted to redder wavelengths by the time it reaches us here and we see it. For very high redshifts (i.e., the farthermost objects from us), that visible light is mostly shifted into the near- and mid-infrared part of the electromagnetic spectrum. For that very reason, to see the first stars and galaxies, we need a potent near- and mid-infrared telescope, which is exactly what Webb is!

Why understanding first stars is important?

The emergence of first stars marks the conclusion of the “Dark Ages” in cosmic history, an epoch characterized by the absence of discrete sources of light. Understanding these first sources of light is crucial, since they critically influenced the formation of later objects such as galaxies. The first sources of light in fact acted as seeds for the later formation of larger objects. Moreover, the first stars that exploded as supernovae might have collapsed even further to form black holes. The black holes began to swallow gas and other stars to become objects identified as “mini-quasars,” which grew and merged to become the huge black holes now present at the centers of almost all massive galaxies.