Lyman-alpha emission

Definition

Lyman-alpha emission is a type of ultraviolet radiation emitted when an electron in a hydrogen atom transitions from the second energy level to the first energy level. This transition releases a photon with a specific wavelength of 121.6 nanometers, which is known as the Lyman-alpha line. This emission is particularly important in the study of distant galaxies and the early universe.

5 Must Know Facts For Your Next Test

1. Lyman-alpha emission is a signature of neutral hydrogen in the early universe, as it is produced when hydrogen atoms absorb and re-emit ultraviolet photons.
2. The Lyman-alpha line is one of the most prominent features in the spectra of high-redshift galaxies, as it is often the only visible emission line due to the expansion of the universe.
3. Lyman-alpha emitters are a class of galaxies that are identified by their strong Lyman-alpha emission, which can be used to study the formation and evolution of galaxies in the early universe.
4. The observed redshift of the Lyman-alpha line can be used to measure the distance and recession velocity of distant galaxies, providing insights into the expansion of the universe.
5. Lyman-alpha radiation can also be used to probe the properties of the intergalactic medium, such as the distribution and density of neutral hydrogen, which can reveal information about the reionization of the universe.

Review Questions

• Explain the physical process that leads to Lyman-alpha emission in hydrogen atoms.
  • Lyman-alpha emission occurs when an electron in a hydrogen atom transitions from the second energy level (n=2) to the first energy level (n=1). This transition releases a photon with a specific wavelength of 121.6 nanometers, which is known as the Lyman-alpha line. This emission is a signature of neutral hydrogen and is particularly important for studying the properties and evolution of distant galaxies in the early universe.
• Describe how the Lyman-alpha line can be used to study the properties of the intergalactic medium.
  • The observed redshift of the Lyman-alpha line can provide information about the distribution and density of neutral hydrogen in the intergalactic medium. As the light from distant galaxies travels through the expanding universe, the Lyman-alpha photons are shifted to longer wavelengths, which can be used to measure the recession velocity and distance of the galaxies. By analyzing the properties of the Lyman-alpha line, such as its strength and profile, astronomers can also study the properties of the intergalactic medium, including its temperature, ionization state, and the presence of other elements, which can reveal important insights about the reionization of the universe.
• Evaluate the significance of Lyman-alpha emitters in the study of galaxy formation and evolution in the early universe.
  • Lyman-alpha emitters, which are galaxies identified by their strong Lyman-alpha emission, are crucial for understanding the formation and evolution of galaxies in the early universe. The Lyman-alpha line is often the only visible emission line in the spectra of high-redshift galaxies due to the expansion of the universe, making it a valuable tool for studying these distant objects. By analyzing the properties of Lyman-alpha emitters, such as their luminosity, spatial distribution, and clustering, astronomers can gain insights into the processes that govern galaxy formation, including the role of dark matter, the impact of feedback from star formation and active galactic nuclei, and the influence of the intergalactic medium. The study of Lyman-alpha emitters has the potential to shed light on the early stages of structure formation in the universe and the evolution of galaxies over cosmic time.

Related terms

Hydrogen atom: The simplest and most abundant element in the universe, consisting of a single proton and a single electron.

Electron transition: The movement of an electron from one energy level to another within an atom, which can result in the emission or absorption of a photon.

Ultraviolet radiation: Electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, which is important for various processes in astronomy and astrophysics.