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🟠 Brown Dwarf Classifier & Cooling Simulation

Interactive brown dwarf simulation: adjust mass to classify a body as a star, brown dwarf or giant planet, and watch it cool and dim through L, T and Y spectral classes over time.

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This interactive brown dwarf simulation lets you classify a substellar object by mass and watch it cool and dim over millions of years, tracing its path through the L, T and Y spectral classes on a live temperature-versus-time cooling curve.

🔬 What It Demonstrates

Below about 13 Jupiter masses, an object cannot ignite even deuterium fusion and is classed as a giant planet. Between roughly 13 and 80 Jupiter masses, brief deuterium fusion occurs but core temperatures never reach the ~7-8 million K needed to sustain hydrogen fusion — these are brown dwarfs, "failed stars" that simply cool and dim forever. Above ~80 Jupiter masses, sustained hydrogen fusion begins and the object becomes a true star, holding a roughly steady temperature indefinitely.

🎮 How to Use

Drag the mass slider from giant-planet territory up through the brown-dwarf range to the stellar limit and watch the classification badge update instantly. Increase cooling speed to fast-forward time and watch the object's colour shift from white-hot to deep red as it cools, while the graph plots its full thermal history.

💡 Did You Know?

Because brown dwarfs cool continuously, their observed temperature alone cannot reveal their age or mass without also knowing how long they have been cooling — a fundamental degeneracy that makes brown dwarf science especially tricky compared with normal stars.

About the Brown Dwarf Simulation

Brown dwarfs occupy the mass gap between giant planets and true stars — objects with roughly 13 to 80 times the mass of Jupiter. This simulation models the boundary conditions astronomers use to distinguish the three categories: below 13 Jupiter masses, core pressure and temperature never rise enough for any fusion; between 13 and 80 Jupiter masses, brief deuterium fusion occurs early on but cannot be sustained, so the object simply radiates away its formation heat and cools indefinitely; above roughly 80 Jupiter masses, core temperature and pressure are sufficient to sustain ordinary hydrogen fusion, and the object settles onto the main sequence as a true, long-lived star.

Because they have no long-term energy source, brown dwarfs cool and dim continuously over billions of years, drifting through decreasing-temperature spectral classes first defined for cool stars and then extended specifically for brown dwarfs: L dwarfs (roughly 1300–2500 K, dusty red-brown atmospheres), T dwarfs (roughly 500–1300 K, methane absorption bands), and the coldest known Y dwarfs (below about 500 K, water-cloud atmospheres approaching the temperature of a warm oven).

🔬 The physics

Cooling follows a power-law decline in temperature with time, with heavier objects retaining heat longer because they have more thermal mass relative to their radiating surface.

🎮 Controls

Mass determines classification and initial formation temperature; cooling speed fast-forwards simulated millions of years so you can watch the full thermal evolution play out.

💡 Spectral classes

L, T and Y spectral classes were introduced specifically to describe brown dwarfs too cool to fit the traditional O, B, A, F, G, K, M stellar sequence.

Frequently Asked Questions

What exactly is a brown dwarf?

A brown dwarf is a substellar object more massive than a giant planet but not massive enough to sustain hydrogen fusion in its core. It briefly fuses deuterium after formation but then simply cools and dims for the rest of its existence, earning the nickname "failed star."

What mass separates a giant planet, a brown dwarf and a star?

The commonly used boundaries are about 13 Jupiter masses (below which no fusion of any kind occurs, defining a planet) and about 80 Jupiter masses (above which sustained hydrogen fusion begins, defining a true star). Objects in between are brown dwarfs.

Why do brown dwarfs keep cooling forever?

Without a sustained internal energy source like hydrogen fusion, a brown dwarf can only radiate away the heat left over from its formation and from its brief early deuterium burning. With nothing replenishing that heat, its temperature and luminosity decline steadily over billions of years.

What are L, T and Y spectral classes?

They are temperature-based spectral classes introduced to describe cool substellar objects. L dwarfs are the warmest and reddest, T dwarfs are cooler with methane absorption in their spectra, and Y dwarfs are the coldest known, some with atmospheric temperatures near room temperature.

Can you tell a brown dwarf's age just from its temperature?

Not on its own. Because brown dwarfs of different masses can have the same temperature at different ages — a heavier one cooling from a hotter starting point, a lighter one having cooled for longer — astronomers need independent age or mass estimates to break this degeneracy.

⚙ Under the hood

Adjust mass to classify a brown dwarf, star, or giant planet, and watch its cooling curve and colour shift over time.

brown dwarfsubstellar objectcooling curvestellar classificationspectral type

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