Astronomers have used a lens bigger than a galaxy to observe the faintest and youngest galaxies ever found. This lens isn’t one we’ve built, but a naturally occurring one, and it’s made entirely of gravity.
One of the properties of gravity is that large masses can cause light near them to change direction, or “bend” due to their gravity. So when a distant object is behind a galaxy or cluster of galaxies, it’s light is bent to gravitationally lens the distant object. Because of this lensing effect, we actually receive more light from the distant object than we normally would. Much like a telescope, a gravitational lens magnifies the light we observe from distant objects.
This latest work used observations from the Hubble space telescope’s Frontier Fields project, which observed distant clusters of galaxies. These clusters magnified more distant dwarf galaxies behind them. What the team observed about 250 dwarf galaxies from a period when the universe was only about 600 – 900 million years old. They found that these early dwarf galaxies played a key role in a process known as reionization, when neutral hydrogen in the universe was ionized by ultraviolet light.
Paper: H. Atek et al. Are Ultra-faint Galaxies at z = 6−8 Responsible for Cosmic Reionization? Combined Constraints from the Hubble Frontier Fields Clusters And Parallels. to appear in the Astrophysical Journal (2015)