http://www.sciencemag.org/news/2018/11/large-strangely-dim-galaxy-found-lurking-far-side-milky-way

Antlia 2 (upper left), hidden on the Milky Way's far side, is as big as the Large Magellanic Cloud (lower right) but much dimmer. (A bright, artificial blob representing Antlia 2 was added to show its location.)

Circling our galaxy is a stealthy giant. Astronomers have discovered a dwarf galaxy, called Antlia 2, that is one-third the size of the Milky Way itself. As big as the Large Magellanic Cloud, the galaxy’s largest companion, Antlia 2 eluded detection until now because it is 10,000 times fainter. Such a strange beast challenges models of galaxy formation and dark matter, the unseen stuff that helps pull galaxies together.