Brown Dwarf

Definition

A brown dwarf is a substellar object that is too massive to be considered a planet, but not massive enough to sustain hydrogen fusion in its core like a star. These objects occupy the mass range between the heaviest gas giant planets and the lightest stars.

5 Must Know Facts For Your Next Test

1. Brown dwarfs are often referred to as 'failed stars' because they lack the mass necessary to sustain hydrogen fusion in their cores.
2. They can, however, undergo deuterium fusion, which provides a small amount of energy and contributes to their overall luminosity.
3. Brown dwarfs are believed to form through the same process as stars, starting with the gravitational collapse of a cloud of gas and dust once it exceeds the Jeans mass.
4. The mass range for brown dwarfs is typically between 13 and 80 times the mass of Jupiter, with the lower limit defined by the minimum mass required for deuterium fusion.
5. Unlike stars, brown dwarfs do not have a stable nuclear fusion process in their cores and gradually cool over time, emitting infrared radiation.

Review Questions

• Explain how the process of star formation relates to the formation of brown dwarfs.
  • Brown dwarfs are believed to form through the same gravitational collapse process as stars, starting with a cloud of gas and dust that exceeds the Jeans mass. However, unlike stars, brown dwarfs do not have enough mass to sustain stable hydrogen fusion in their cores. Instead, they can undergo deuterium fusion, which provides a small amount of energy and contributes to their overall luminosity. The mass range for brown dwarfs is typically between 13 and 80 times the mass of Jupiter, with the lower limit defined by the minimum mass required for deuterium fusion to occur.
• Describe the key differences between brown dwarfs and stars in terms of their physical properties and energy production mechanisms.
  • The primary difference between brown dwarfs and stars is that brown dwarfs lack the mass necessary to sustain stable hydrogen fusion in their cores, which is the defining feature of a star. While stars can maintain a stable nuclear fusion process, brown dwarfs gradually cool over time and emit infrared radiation. Additionally, brown dwarfs can undergo deuterium fusion, which provides a small amount of energy, but is not enough to sustain the object as a star. The mass range for brown dwarfs is also significantly lower than that of stars, typically between 13 and 80 times the mass of Jupiter, with the lower limit defined by the minimum mass required for deuterium fusion.
• Analyze the role of the Jeans mass in the formation of both stars and brown dwarfs, and explain how this concept is related to the distinction between these two types of celestial objects.
  • The Jeans mass is the minimum mass required for a cloud of gas and dust to gravitationally collapse and form either a star or a brown dwarf. If the mass of the cloud exceeds the Jeans mass, it will begin to collapse under its own gravity. However, the ultimate fate of the collapsing cloud depends on its total mass. If the cloud has enough mass to sustain stable hydrogen fusion in its core, it will become a star. If the cloud has a mass that falls within the brown dwarf range, typically between 13 and 80 times the mass of Jupiter, it will become a brown dwarf. The Jeans mass, therefore, represents the critical threshold that determines whether a collapsing cloud of gas and dust will form a star or a brown dwarf, highlighting the key distinction between these two types of celestial objects.

Related terms

Substellar Object: A substellar object is any celestial body that is not massive enough to sustain stable hydrogen fusion in its core, the defining feature of a star.

Deuterium Fusion: Deuterium fusion is a nuclear fusion process that can occur in brown dwarfs and other substellar objects, where deuterium (a heavy isotope of hydrogen) is fused into helium, releasing a small amount of energy.

Jeans Mass: The Jeans mass is the minimum mass required for a cloud of gas and dust to gravitationally collapse under its own weight and form a star or brown dwarf.