What’s the Difference Between a Main Sequence Star and a Brown Dwarf?
Hello, all you curious stargazers. Today, I wanted to tell you about something really cool–when we discover how complex and amazing science can be in our own backyard. What we’ll do today is look at two very different types of stars. The first type we will look at is called a “main-sequence” star and the second type we will look at is called a “brown-dwarf.” Although both may appear as just one dot of light through your telescope or binoculars, they have very different and interesting histories. So, let’s start to learn about what makes each of these celestial objects work.
Main Sequence Stars: The Cosmic Powerhouses
Main Sequence Stars Are The “Rock Stars” Of The Star World.
Our sun is one such example. A main sequence star has a core that generates an enormous amount of energy through a phenomenal process called nuclear fusion (a process in which hydrogen atoms collide and merge into helium). This tremendous amount of energy produced in this manner allows the star to emit light for BILLIONS of years. It is the nuclear fusion at the cores of these stars that creates their stable and lengthy glow and enables the existence of planetary bodies with conditions capable of harboring life.
A main sequence star can be thought of as a stellar furnace that is perfectly balanced between gravitational collapse inward and outward explosive force generated by nuclear fusion preventing this collapse. These stars exist in a variety of sizes ranging from small, faintly glowing red dwarfs to large, short-lived, intensely burning blue giants. Regardless of the size, each main sequence star is sustained in its position on the Hertzsprung Russell Diagram, or “stellar family photo,” by its ongoing nuclear fusion.
Brown Dwarfs: The Almost Stars
Brown dwarfs, sometimes referred to as “failed stars”, do not have sufficient mass to maintain the constant Hydrogen fusion required for main sequence stars. Brown dwarfs fall in between large planets and small stars in terms of size. A minimum mass of roughly 8% of the sun’s mass will classify a star as a brown dwarf, therefore, brown dwarfs are classified as objects with insufficient mass to achieve sustained Hydrogen fusion. Due to lack of continual Hydrogen fusion, brown dwarfs produce light that is faint compared to stars. The faint light produced by brown dwarfs is primarily due to residual heat generated during the formation of the object, with some fusions occurring with heavier elements like deuterium (a rare form of hydrogen). Overall, brown dwarfs are cool, dim and relatively shy when compared to stars. However, what is exciting about brown dwarfs is they challenge our definition of what constitutes a planet or a star—do they fit into one category or another? As we continue to develop and enhance our telescopes and infrared sensors, brown dwarfs are becoming more prominent in the study of star formation and the diversity of objects in our galaxy.
So, why does this matter?
Able to tell the difference between a main sequence star and a brown dwarf is not simply a matter of astronomy trivia; it is also about appreciating the lifecycle of celestial bodies and the delicate thresholds that nature uses to create a star, or to stop a star from being born. This skill will allow astronomers to better understand the process of stellar evolution and to identify new types of objects which will provide us with additional information regarding our universe.
The next time you gaze upward into the night sky, perhaps you may imagine that one or two of the faint dots located near other stars are brown dwarfs, small and dimly lit and they exist very quietly. There is something quiet, and in many ways magical, about this existence.
Until Next Time
Thank you for joining me on this cosmic journey! If you enjoyed this one, keep an eye out because next week I will be exploring the enigmatic lives of white dwarfs—those “retired” stars whose tales span billions of years. Meanwhile, just continue to look up to the sky, remain curious and allow the stars to inspire your imagination.