Rick Robinson

May 21st 2018

What Is a Brown Dwarf?


The Milky Way is home to approximately 100 billion brown dwarfs, reports Sky & Telescope. Brown dwarfs are often wrongly called “failed stars,” but they are neither a planet nor a star, raising the question: What is a brown dwarf?

Defining Brown Dwarfs

Brown dwarfs are a recent discovery; their existence was confirmed in 1995, according to NASA. They are neither planets nor stars but are often confused for both. Forbes helps differentiate among the three: “Bodies smaller than 10 Jupiter masses are planets, larger than 90 Jupiter masses are stars, and in between are brown dwarfs that share properties similar to both.”

Although they form like stars, brown dwarfs are less massive and aren’t hot enough to sustain the hydrogen fusion reaction that allows stars to shine, according to NASA. Brown dwarfs are often mistaken for planets because of their sizes and similar atmospheres. As noted by, brown dwarfs and planets have atmospheres conducive to cloud formations as well as storms, and, similar to stars, brown dwarfs can host their own planets. Weighing in at about one-tenth the mass of the Sun, brown dwarfs can range from 13 to 90 times the mass of Jupiter.

When we fully understand brown dwarfs, we will truly understand the possibilities for life in the universe.

Hunting the Elusive

Unlike stars, brown dwarfs cool and fade as they age, emitting infrared light invisible to the human eye. Earth’s atmosphere absorbs water vapor emitted by brown dwarfs, which makes an infrared observation using ground-based telescopes both difficult and limited, like searching for candles in a floodlit fog.

That’s where NASA’s James Webb Space Telescope comes in. Equipped with several infrared-detecting instruments, the telescope will allow several NASA research teams to investigate brown dwarfs. One team plans to investigate a nearby brown dwarf known as SIMP0136. Because of its low temperature, the outer layers of this brown dwarf are believed to resemble the atmosphere of a planet. And with no bright star nearby, researchers will be able to observe it without interference.

Another team will investigate brown dwarfs in a star cluster and associated nebula known as NGC 1333, in the constellation Perseus. NGC 1333, known as a stellar nursery, harbors an unusually high number of brown dwarfs. Its newly formed brown dwarfs shine more brightly because they haven’t had time to cool down, allowing astronomers to study brown dwarfs not much heavier than Jupiter. The findings will help us draw a more distinct line between brown dwarfs and giant planets.

If these missions are successful, the James Webb Space Telescope could be used to search for future exoplanet observation, according to Johns Hopkins University.

The Strange Universe

So what is a brown dwarf? With the help of the James Webb Space Telescope, we hope to find more answers to this question. It’s one more example that our galaxy is more complex and varied than anyone imagined only a few decades ago. The universe is rich and strange, and it only grows even richer and stranger the more we explore it.