Space Telescope Science
As powerful as NASA’s Hubble and Spitzer space telescopes are, they need a little help from nature in seeking out the farthest, and hence earliest galaxies that first appeared in the universe after the big bang. This help comes from a natural zoom lens in the universe, formed by the warping of space by intense gravitational fields.
The most powerful “zoom lenses” out there are formed by very massive foreground clusters that bend space like a bowling ball rolling across a soft mattress. The lens boosts the brightness of distant background objects. The farthest candidates simply appear as red dots in Hubble photos because of their small size and great distance.
However, astronomers got very lucky when they looked at galaxy cluster SPT-CL J0615-5746. Embedded in the photo is an arc-like structure that is not only the amplified image of a background galaxy, but an image that has been smeared into a crescent-shape. This image allowed astronomers to estimate that the diminutive galaxy weighs in at no more than 3 billion solar masses (roughly 1/100th the mass of our fully grown Milky Way galaxy). It is less than 2,500 light-years across, half the size of the Small Magellanic Cloud, a satellite galaxy of our Milky Way. The object is considered prototypical of young galaxies that emerged during the epoch shortly after the big bang. Hubble’s clarity, combined with Spitzer’s infrared sensitivity to light reddened by the expanding universe, allowed for the object’s vast distance to be calculated.