Brown Dwarfs: Objects that Are Between Planets and Stars

by Carson
Brown dwarf

Do you know that there is some celestial objects have masses that are between planets and stars? They are called brown dwarfs, and we’ll find out about them in this article.

What Make Brown Dwarfs Special?

You may think that brown dwarfs are not special because it doesn’t undergo regular nuclear fusion, so they don’t glow. However, brown dwarfs can fuse deuterium but cannot fuse hydrogen even if it has hydrogen supply, which is a condition that neither stars nor planets cannot satisfy. Specifically, planets cannot fuse deuterium or hydrogen, and stars can fuse hydrogen and fuse heavier elements if the star has run out of hydrogen.

What is the mass required for an object to become a brown dwarf? 13 Jupiter masses are necessary for deuterium to be fused at the object’s core, and 80 Jupiter masses are needed for an object to collapse on itself so much that hydrogen in it starts to fuse. Therefore, a brown dwarf is an object whose mass is 13 to 80 times the mass of Jupiter.

How Does Deuterium Fusion Work?

Main-sequence stars fuse hydrogen into helium to counteract the force of gravity that is causing it to collapse in on itself, making a balance and maintaining the integrity of a star. In this process, protons collide so that some of them become neutrons, and the entire thing becomes helium-4 nuclei. But in deuterium fusion, something different happens.

Remember that deuterium is just an isotope of hydrogen with one neutron, and it’s essentially hydrogen-2. Therefore, a collision between this nucleus and a proton produces a helium-3 nucleus, which is the reaction that powers the deuterium fusion occurring inside the center of brown dwarfs.

The Evolution of a Brown Dwarf

At first, a brown dwarf evolves like a star. They are formed by clouds of interstellar dust and collapse under the force of gravity. Depending on the mass of the resulting object, it is either a planet, a brown dwarf, or a star. Another way for them to form is similar to the process of creating gaseous planets, in which the brown dwarf forms from the collapse of a gas cloud other than the most massive cloud of gas and dust in the planetary system.

However, once a brown dwarf starts fusing deuterium, it evolves differently from stars. Because deuterium is a relatively rare resource in the core of brown dwarfs, they can only fuse it into helium for about 10 million years before its supply runs out, after which it behaves like a normal gaseous planet.


In this article, we’ve mentioned the primary features of brown dwarfs, including what separates brown dwarfs from planets and stars. If you want to learn more about them, please visit the webpages in the references below.

References and Credits

  1. (n.d.). Brown Dwarf. Retrieved January 3, 2022, from
  2. (n.d.). Stars & Brown Dwarfs. Retrieved January 3, 2022, from
  3. (2020, September 5). What are brown dwarfs? Retrieved January 3, 2022, from
  4. Paul Sutter. (2019, January 3). Brown Dwarfs: The Coolest Stars or the Hottest Planets? Retrieved January 3, 2022, from
  5. (n.d.). Star Life and Death. Retrieved January 3, 2022, from

Related Posts

Leave a Comment

* By using this form you agree with the storage and handling of your data by this website.