Cosmology: Dark Ages, Reionization, and The First Stars
The early universe was a place shrouded in darkness and mystery, now known as the Dark Ages. Immediately following the Big Bang and prior to the formation of stars, the universe consisted primarily of unassociated hydrogen and helium. The Dark Ages lasted until the universe reached a certain temperature, and reionization occurred. After the initial reionization event, the first stars began to appear and the universe changed once again.
The Dark Ages
The Dark Ages began shortly after the Big Bang and lasted until about 150 million years later. Prior to this time, the universe was cooling and contracting, with only hydrogen and helium gas. This gas was too diffuse to form any stars, and so the sky was kept in darkness by the lack of energy.
Reionization
As the temperature of the universe cooled, it eventually reached 200,000 degrees Celsius or higher – hot enough to ionize the hydrogen. This event, known as reionization, caused the gas to become separated and finally form the first stars. Before this, the universe was truly in darkness, as cosmologists had nothing hints of what was to come next.
The First Stars
After the initial reionization event, the universe began to fill with the light of the first stars. These stars were the first bodies to form in the universe and were much hotter, larger, and brighter than stars today. They emitted light and ultraviolet radiation, which filled the universe and caused further reionization as ions recombined. This second reionization event caused further separation of the hydrogen from the helium, and eventually allowed for heavier elements to form, paving the way for the formation of more stars and galaxies.
The Dark Ages, reionization, and the first stars have had a profound effect on the universe and our understanding of it. They represent a mysterious and unknown time in the universe’s history that we are still striving to understand.
Cosmology has come a long way since the early days of the universe. One of the most studied periods of the universe is known as the “Dark Ages”. The Dark Ages referred to the period of time in our universe that pre-dates stars and galaxies, roughly13.7 billion years ago. During this period, the intensity of light was so low that typically, the only sources of light were the cosmic microwave background and black holes.
Following the Dark Ages, a period of cosmic history known as the Reionization Era began. This was a period of time when interstellar gas, or “hydrogen gas”, in the intergalactic medium was re-ionized by energy from the first stars to form. This marks the transition from a neutral atomic universe to an ionized plasma universe, as well as a higher rate of star formation.
The first stars that formed during the Reionization Period were much more massive than the stars we know today. These massive stars burned through their supply of fuel much faster, supernovas more quickly, and released more ultraviolet radiation than today’s stars. This ultraviolet radiation was absorbed by the surrounding hydrogen gas, leading to its re-ionization.
The re-ionization of the intergalactic medium paved the way for a new period of star formation, with stars of all sizes and masses forming throughout the universe. This marks the beginning of the formations of galaxies and galactic structures, such as stellar nurseries, star clusters and supernovas. This period is also significant in terms of the study of cosmology, as it marks the transition from a universe filled with hot gas to one filled with stars and galaxies.
Through the study of cosmology, we can observe the period of time in the universe’s history known as the Dark Ages, the transition to the Reionization Period and the formation of the first stars. Working together, these three key events have shaped the universe into the one we know today.