Young brown dwarfs are now known to exist in the hundreds in the Sun's neighbourhood. The methane, or 'T-type', brown dwarfs are the coolest objects so far detected. More about LL And and EF Eri LL Andromedae is classified as a 'dwarf nova'. It is a binary star system in which material flows from one star to the other. The two members are a white dwarf primary, which receives material, and a cool dwarf secondary, which acts as 'donor'.
Material flowing from the donor star forms a disc around the more massive white dwarf.
Outbursts take place from time to time when hot regions develop on this accretion disc. The outbursts of LL Andromedae, which is a very old system, are spaced by several years, or even decades. In younger dwarf novae, outburst may occur much more frequently. EF Eridani is classified as a 'polar'. Polars are similar to a dwarf novae except that their white dwarfs are strongly magnetic.