What are the L, T, and Y brown dwarfs, which are cooler than M-type stars, sometimes called?

Answer

Failed stars

Objects that fall outside the standard sequence and are cooler than M-type stars, such as L, T, and Y brown dwarfs, are sometimes called 'failed stars.'

What are the L, T, and Y brown dwarfs, which are cooler than M-type stars, sometimes called?
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