With the final observation of the distant galaxy cluster Abell 370 — some 5 billion light-years away — the Hubble Space Telescope’s Frontier Fields program came to an end. The arcs and streaks in the picture are the stretched images of background galaxies, caused by gravitational lensing by Abell 370. Image via NASA/ ESA/ Hubble/ HST Frontier Fields.

The Hubble Space Telescope’s Frontier Fields program has ended, NASA said on May 4, 2017 as it released the image above. This program was born in early 2012, over lunch meetings the Space Telescope Science Institute (STScI) in Baltimore. Ken Sembach, now STScI’s director, said at the time that the program grew from an earlier probe of the universe by Hubble ‰ÛÒ the Hubble Ultra Deep Field ‰ÛÒ which had looked back approximately 13 billion years, between 400 and 800 million years after the Big Bang. Sembach said:

We are often asked by the public whether what is seen in the [Hubble Ultra Deep Field] is typical of the rest of the universe. And quite frankly, we don’t know without further deep observations of this type.

Thus Frontier Fields was born, aimed to advance knowledge of the early universe by studying high-redshift galaxies with the help of gravitational lensing. That is, the immense gravity of massive clusters of galaxies is known to warp the light from even-more-distant galaxies beyond. The intervening clusters distort and magnify the light of the more distant galaxies — too faint to be seen by Hubble directly — so that they become visible. NASA said: