Entitled 'WISE J0304-2705', the object was a member of the recently established 'Y dwarf' class, the coolest stellar temperature class yet defined, added to the end of the sequence OBAFGKMLT
. Although its temperature was not far off that of our own world, the object was not like the rocky Earth-like planets and instead was a giant ball of gas like Jupiter.
Recent surprises: (a) L-type spectra (with strong features due to the alkali metals lithium, sodium, and so forth) switch over to T-type spectra (with features due mostly to methane) over a very narrow range of temperatures near 1,300 Kelvin, accounting for the absence of transitional types and representing the sharpest change between adjacent spectral types anywhere along the sequence OBAFGKMLT
. And (b), among the cooler Ls, a sodium feature removes so much yellow light that a suitably tuned detector might record the complementary color--you may never see a purple cow, but purple stars are possible.