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Brown dwarfs are often called failed stars, being too massive to be considered planets, but not massive enough to become true stars. Brown dwarfs are also different one from the other: they are classified in different classes and as time goes on, they cool, changing their color. In this activity, students will learn about the stellar evolution of brown dwarfs, making models out of styrofoam spheres.
What are brown dwarfs?
Brown dwarfs are objects that fall somewhere between giant gas planets (like Jupiter) and small stars. They’re too massive to be considered planets, but not massive enough to become true stars. Because of their relatively low mass, brown dwarfs can’t generate the extreme temperatures and pressures in their cores that are needed to start nuclear fusion—the process that powers stars and makes them shine. As a result, brown dwarfs give off only a small amount of light, which is why they’re often called “failed stars.”
Image 1: Comparison of the Brown Dwarf with other celestial bodies. Source: Wikipedia.
Most brown dwarfs have surface temperatures ranging from about 600 to 3500 K. (For comparison, the Sun’s surface temperature is about 5800 K.) Their masses are also much smaller—just a few percent of the Sun’s mass. This low temperature and mass mean that brown dwarfs show up in a specific region on the Hertzsprung-Russell diagram, which astronomers use to track the life and evolution of stars. You’ll find brown dwarfs in the bottom right corner—where the coolest, least massive, and dimmest objects live.
Image 2: Position of brown dwarfs in the Hertzsprung-Russell diagram. Source: Steven Dutch of UW Green Boy.
Spectral Classes of Brown Dwarfs
Even though they're called "brown" dwarfs, these objects come in a variety of colours. Their colour depends on their temperature. As brown dwarfs age, they cool down and change the kind of light they emit. These changes are grouped into spectral classes, which help scientists understand what stage a brown dwarf is in.
Spectral Class M: These are the hottest and largest brown dwarfs and have very low luminosity, meaning they’re too dim to be seen with the naked eye.
Image 3: Artist's conception of a brown dwarf of spectral class M. Source: NASA.
Spectral Class L: Cooler than Class M, most L-type brown dwarfs appear dark red and have colder atmospheres.
Image 4: Artist's conception of a brown dwarf of spectral class L. Source: NASA.
Spectral Class T: These brown dwarfs are even cooler, with temperatures between 550 and 1300 K. They are practically invisible to us.
Image 5: Artist's conception of a brown dwarf of spectral class T. Source: NASA.
Spectral Class Y: The coldest of all, Y-class brown dwarfs are cooler than Class T and can have masses between 9 and 25 times that of Jupiter.
Image 6: Artist's conception of a brown dwarf of spectral class Y. Source: NASA.
To know more:
https://en.wikipedia.org/wiki/Brown_dwarf
https://www.britannica.com/science/brown-dwarf
Step 1: Show students the images referring to brown dwarfs and their spectral classes.
Step 2: Hand out the materials for the construction of the model and explain to the students that they should build a brown dwarf of each spectral class.
Step 3: Construction and painting the Brown Dwarfs.
Image 7: Painting the brown dwarfs
Step 4: After construction, students should classify the brown dwarfs by color, according to the Hertzsprung-Russell diagram, and explain their characteristics to their classmates.
Image 8: Classification of brown dwarfs
The evaluation of knowledge will occur through the making of Brown Dwarfs. Students should build a Brown Dwarf of each spectral class and then explain why these substars have different colors.
This activity can be used in the curricular subjects of Physics, Astronomy and Chemistry.
