BROWN DWARFS

Source: HINDU

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Context

• Webb Telescope has provided detailed weather maps of brown dwarfs, revealing blazingly hot temperatures and toxic atmospheric conditions​​.

Details

• Atmospheric Composition: Dominated by hydrogen and helium, with trace amounts of water vapor, methane, and carbon monoxide​​. Clouds composed of silicate particles, resembling hot Saharan dust storms​​.
• Temperature: Cloud tops can reach about 1,700 degrees Fahrenheit (925 degrees Celsius)​.
• Weather Patterns: Fast rotation drives weather patterns, with features similar to Jupiter's Great Red Spot​​.

Brown Dwarfs

• Brown dwarfs are astronomical objects with masses between the heaviest gas giant planets and the lightest stars. They are often called "failed stars" because they cannot sustain hydrogen fusion in their cores.
• Mass Range: Typically between 13 and 80 Jupiter masses​.
• Spectral Types: Classified as L, T, and Y dwarfs, based on their temperatures and spectral characteristics​.

Characteristics

• Formation Process: Similar to stars, brown dwarfs form from the collapse of a gas cloud​​. They do not accumulate enough mass to ignite hydrogen fusion.
• Fusion: Can burn deuterium if they are above approximately 13 Jupiter masses, but this process is short-lived.
• Temperature:
  • L dwarfs: 1,300 to 2,000 K
  • T dwarfs: 700 to 1,300 K
  • Y dwarfs: Below 700 K​
    

Detection

• Infrared Observations: Due to their low temperatures and faint visibility in the optical spectrum, brown dwarfs are primarily detected through infrared observations​​.
• Key Instruments:
  • Wide-field Infrared Survey Explorer (WISE)
  • Vera C. Rubin Observatory​

Role in Galactic Evolution

• Galactic Tracers: Brown dwarfs provide valuable insights into the formation and evolution of the Milky Way​.
• Long-term Stability: Their longevity and abundance make them excellent tracers for studying the early history of our galaxy​.

Evolution

• Binary Systems: Some brown dwarfs start as binary systems but often drift apart over time due to weak gravitational binding and interactions with other stellar objects​​.
• Lifecycle:
  • Born from the gravitational collapse of molecular clouds.
  • Cool and contract over time​

James Webb Space Telescope (JWST)

• Mission: Launched by NASA with contributions from ESA and CSA, JWST is the premier space observatory designed to succeed the Hubble Space Telescope.
• Objectives: To study the formation of stars and planets, the evolution of galaxies, and to search for potentially habitable exoplanets.

Technical Specifications

• Instruments: Equipped with the Near Infrared Camera (NIRCam), Mid-Infrared Instrument (MIRI), Near Infrared Spectrograph (NIRSpec), and Fine Guidance Sensor/Near InfraRed Imager and Slitless Spectrograph (FGS/NIRISS).
• Location: Operates at the second Lagrange point (L2), about 1.5 million kilometers from Earth, providing a stable environment free from Earth's infrared interference.

Achievements and Discoveries

• Early Universe: Provides unprecedented views of the early universe, observing light from the first galaxies formed after the Big Bang.
• Exoplanet Atmospheres: Enables detailed study of exoplanet atmospheres, detecting water vapor, methane, and other potential biomarkers.
• Stellar Nurseries: Investigates regions of star formation, uncovering the processes that lead to the birth of stars and planetary systems.

Type of Dwarf	Description	Characteristics	Examples
White Dwarfs	Stellar remnants from medium-sized stars	Extremely dense, no longer undergo fusion, composed mainly of carbon and oxygen, small size, high gravity, faint luminosity	Sirius B, Procyon B, Van Maanen's Star
Red Dwarfs	Small, cool, and long-lived stars	Burn hydrogen slowly, can live for trillions of years, end as white dwarfs	Proxima Centauri
Brown Dwarfs	Substellar objects not massive enough for hydrogen fusion	Mass between the heaviest gas giant planets and the lightest stars, emits primarily in infrared	Luhman 16, Gliese 229B

Sources:

HINDU

PRACTICE QUESTION Q: Consider the following statements about brown dwarfs: Brown dwarfs form through gravitational collapse like stars but do not ignite nuclear fusion. The smallest brown dwarfs can have masses comparable to giant planets. Brown dwarfs emit primarily in the visible spectrum. Which of the above statements are correct? A) 1 and 2 only B) 2 and 3 only C) 1 and 3 only D) 1, 2, and 3 Answer: A