Cosmic dark ages

Definition

The cosmic dark ages refer to a period in the early universe, roughly from 380,000 years to about 1 billion years after the Big Bang, when the universe was mostly dark and devoid of significant sources of light. During this time, the universe cooled enough for neutral hydrogen to form, leading to a lack of luminous objects like stars and galaxies, creating a vast expanse of darkness in the cosmos.

5 Must Know Facts For Your Next Test

1. The cosmic dark ages followed recombination and lasted until the formation of the first stars, marking a crucial transition in cosmic history.
2. During this period, hydrogen was the primary element in the universe, existing mostly in its neutral state and leading to an opaque universe for radiation.
3. The end of the cosmic dark ages is associated with the emergence of the first luminous objects, which began to illuminate the universe and shape its structure.
4. Observations of the cosmic microwave background provide insights into conditions during the dark ages and can help scientists understand when reionization began.
5. The study of the cosmic dark ages helps astronomers grasp the timeline of structure formation, including how dark matter influenced galaxy formation during this epoch.

Review Questions

• How did recombination impact the transition into the cosmic dark ages?
  • Recombination played a vital role in transitioning into the cosmic dark ages by allowing protons and electrons to combine and form neutral hydrogen. This process occurred around 380,000 years after the Big Bang, making photons free to travel through space without being scattered. The result was a cooling universe where light sources were nearly nonexistent, leading directly into this period of darkness.
• In what ways did dark matter contribute to structure formation during the cosmic dark ages?
  • Dark matter contributed significantly to structure formation during the cosmic dark ages by providing a gravitational framework within which normal matter could accumulate. Although no luminous structures existed yet, dark matter created gravitational wells that would eventually attract baryonic matter, leading to the formation of stars and galaxies. This gravitational influence set the stage for reionization and marked the transition out of the dark ages.
• Evaluate how understanding cosmic dark ages enhances our knowledge of early universe conditions and structure formation.
  • Understanding cosmic dark ages enhances our knowledge by providing context for when and how galaxies began to form after a prolonged period of darkness. The research into this epoch reveals critical insights about conditions in the early universe, including temperature and density profiles. Furthermore, it illuminates how dark matter influenced baryonic matter’s behavior, helping us comprehend not only galaxy formation but also the evolution of cosmic structures over billions of years.

Related terms

recombination: The process that occurred around 380,000 years after the Big Bang when electrons combined with protons to form neutral hydrogen, allowing photons to travel freely and marking the end of the photon-baryon fluid.

cosmic microwave background (CMB): The remnant radiation from the Big Bang, which fills the universe and provides evidence for the early state of the cosmos, becoming visible once the universe transitioned from a hot plasma to a cooler state during recombination.

reionization: The period following the cosmic dark ages when the first stars and galaxies formed, emitting high-energy radiation that ionized neutral hydrogen gas, thus ending the dark ages and leading to a more luminous universe.