If you are seriously interested in learning about the history and meaning of the Sonnenrad I would recommend starting with James Pontolillo’s The Black Sun Unveiled: Genesis and Development of a Modern National Socialist Mythos and Stanton Marlan’s The Black Sun: The Alchemy and Art of Darkness. The first consists largely of primary source material (photographs as well as documents) much of which is obscure and difficult to track down elsewhere – and the second really delves into its esoteric significance. Both have some points I’d quibble with, but are infinitely to be preferred to the sort of info that’s likely circulating on Twitter.