brown dwarf

American  

[broun dwawrf] / ˈbraʊn ˈdwɔrf /

noun

Astronomy.

1. a celestial object smaller than a small star but larger than a giant planet: believed to form as stars do, from collapsing clouds of gas and dust, brown dwarfs are sometimes called failed stars as they are not dense enough to initiate nuclear fusion, leaving them much dimmer and cooler than stars.

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brown dwarf British  

noun

1. a type of celestial body midway in mass between a large planet and a small star

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brown dwarf Scientific  

1. A celestial body with insufficient mass to sustain the nuclear fusion that produces radiant energy in normal stars. It is believed that a brown dwarf is formed with enough mass to start nuclear fusion in its core, but without enough for the fusion to become self-sustaining. Theory suggests that a body with about one percent of the mass of the Sun—or ten times the mass of Jupiter—can generate this initial fusion, but that it needs at least eight percent of the Sun's mass to sustain the fusion. After the fusion ends, the dwarf still glows for a period from radiating heat, with a surface temperature of about 2,500°K (4,532°F) or less.

2. See Note at dwarf star

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Etymology

Origin of brown dwarf

First recorded in 1975–80

Example Sentences

It could be a giant planet, a brown dwarf, or an extremely low-mass star.

From Science Daily • Jan. 24, 2026

With a mass similar to Saturn, the researchers suggest that it most likely formed within a planetary system rather than developing on its own like a small star or brown dwarf.

From Science Daily • Jan. 4, 2026

After carefully studying its dance routine, astronomers think that the white dwarf has a partner, probably another dead star or a brown dwarf.

From Space Scoop • Aug. 11, 2025

Image: The picture shows an artist's recreation of the orbital paths of both brown dwarf stars, in blue, and of the unusually orbiting planet, in orange.

From Space Scoop • May 6, 2025

I’m like that theoretical brown dwarf star or gas giant planet lurking at the far edges of our solar system, way beyond Pluto.

From "Shine!" by J.J. and Chris Grabenstein