Hubble Ultra-Deep FieldThe Hubble Ultra-Deep Field shows galaxies as they were when the Universe was young. Those with the highest estimated redshifts (numbers and insets) were born more than 13 billion years ago, soon after the Big Bang.Image: NASA, ESA, R. Ellis (Caltech), UDF 2012 Team

For one sleepless week in early September 2009, Garth Illingworth and his team had the early Universe all to themselves. At NASA’s request, Illingworth, Rychard Bouwens and Pascal Oesch had just spent the previous week staring into their computer screens at the University of California, Santa Cruz, scanning through hundreds of black-and-white portraits of faint galaxies recorded in a multi-day time exposure by a newly installed infrared camera on the Hubble Space Telescope. NASA simply wanted the three astronomers to preview the images and make sure that the camera was working correctly, before the agency released the data more widely.

But Illingworth, Bouwens and Oesch were hoping that they would find more — that at least some of those smudges of light would prove to be among the first galaxies to form in the Universe, less than 1 billion years after the Big Bang. Even a faint glimpse of such objects could provide fresh insights into some of the biggest questions in cosmology, ranging from the nature of the first stars to the tumultuous beginnings of galaxy formation.

That week, the astronomers began to focus on two dozen tiny candidate images — each so dim and grainy that they might easily be noise in the camera’s digital sensors. But as their analysis proceeded, it became clear that these patches of light had the right color, appearing only in the camera’s reddest filters — exactly what would be expected of newborn galaxies seen at a very great distance and very high redshift. And when the three colleagues started digitally adding together exposures of each candidate, says Illingworth, “suddenly there they were” — fuzzy, but undeniable images of galaxies. “That week in September was one of the most exciting times of my career!”

via Faint Portraits of First Galaxies Shed Light on Cosmic Dawn: Scientific American.