With its infrared vision, Webb will be a potent time machine that can look back 13.5 billion years to observe the first stars and galaxies emerging from the early universe’s darkness.
Why Infrared?
Why does viewing the first stars and galaxies to develop in the cosmos require a potent infrared observatory? Why do we even want to look at the first stars and galaxies?
We haven’t yet had one cause. About 380,000 years after the Big Bang, the microwave COBE and WMAP satellites discovered the heat signature it left behind.
However, there were no stars or galaxies at that time. In actuality, the universe was a rather gloomy place.
The Early Universe
The universe was like a boiling soup of particles after the Big Bang (i.e. protons, neutrons, and electrons).
Protons and neutrons started fusing to form ionized hydrogen atoms as the universe began to cool (and eventually some helium).
The ionized hydrogen and helium atoms attract electrons, converting them into neutral atoms, which for the first time prevents light from being scattered by free electrons.
The universe wasn’t as mysterious anymore! The cosmic dark ages wouldn’t end until the first sources of light began to appear, which might take a while (up to a few hundred million years after the Big Bang!)
It is unknown exactly how the first stars in the universe (stars that fused existing hydrogen atoms into additional helium) appeared or when they originally originated. Webb was created to assist us in finding the answers to some of these problems. See also our Big Bang Q&A with John Mather.
What Is Shifted Light?
Consider the light going from the earliest stars and galaxies about 13.6 billion years ago and arriving at our telescopes. In essence, we are viewing these objects as they were 13.6 billion years ago, when light first entered them.
We refer to this change in color or wavelength toward the red as a “redshift” as it occurs by the time the light reaches us.
Why Does This Happen?
In this instance, it’s because Einstein’s General Relativity comes into play when discussing extremely far-off things. It explains that as the universe expands, things (galaxies) travel farther away from one another as the distance between them widens.
Due to the fact that this light travels to us as infrared light, it can render distant objects very faint (or even undetectable) at visible wavelengths.
Conclusion.
Redshift is the concept that the light that these early stars and galaxies emit, whether it be visible or ultraviolet, actually shifts to redder wavelengths by the time it reaches our current location.
That visible light is typically displaced towards the near- and mid-infrared region of the electromagnetic spectrum with very high redshifts (i.e., the farthest objects from us). We therefore require a strong near-and-mid-infrared telescope, which Webb is, in order to observe the first stars and galaxies.