Astrophys. J (in the press); preprint at http://arxiv.org/abs/1502.01358 (2015)

Cosmological simulations of nearby galaxies have a problem: the predicted abundance of dwarf galaxies in the Local Group of galaxies (whose centre of mass lies between the Milky Way and Andromeda) far outstrips the observed quantity. Could these young, dark-matter-dominated galaxies lie near the Galactic plane, within a region that is not accessible to optical telescopes due to obscuring dust? To find out, Sukanya Chakrabarti and colleagues sifted through a near-infrared database of tens of millions of stars — collected by the VISTA telescope, which can 'see through' dust.

And indeed, they found four Cepheid variables tightly clustered together in angle and in distance, roughly 90 kpc away. These are yellow supergiant stars that pulsate radially, with regular brightness changes on timescales of days or months. At this distance, they are most likely part of a dwarf galaxy whose existence was predicted by Chakrabarti and Leo Blitz. Their previous analysis was based on disturbances in the atomic hydrogen disk of the Milky Way, consistent with tidal imprints from the passage of a small dwarf galaxy through our Galaxy.