The Hunt For The Oldest Galaxies In The Universe

The deeper we look into the vastness of space, the further back in time we are able to see. Now, NASA’s RELICS project is pushing this phenomenon as far as it can in an attempt to observe galaxies that formed at the very beginning of the Universe

- Marcus Chown

As the fireball of the Big Bang expanded and cooled, it went from white-hot to cherry-red before finally fading into invisibility. The Universe was plunged into blackness and the resulting cosmic dark age stretched on interminably. Over time, the Universe doubled in size, doubled once more, over and over again, then, one day, something extraordinary happened. The dark age came to an end. Across the entire length and breadth of the Universe, stars began switch on like lights on a Christmas tree.

The first stars either came together under gravity to create the first galaxies, or were actually born in the clouds of gas and dust that made up the first galaxies. And the hunt to find these first galaxies is hotting up. One project – the Re-ionization Lensing Cluster Survey (RELICS) – has found around 300 galaxies that existed in the first billion years of the Universe’s history. One galaxy in particular is so old that the Universe it occupied was a mere 3 per cent of its present age of 13.82 billion years. Such objects appear in astronomers’ telescopes like persistent after-images, their light having travelled across space for billions upon billions of years before reaching us.

BACK IN TIME

More than 40 astronomers in many countries have been involved in the RELICS project, contributing hundreds of hours of observing time on the Hubble Space Telescope and the Spitzer Space Telescope. However, the principal observing instrument is the Universe itself. The gravitational fields of the massive clusters of galaxies that pepper the Universe act like giant lenses that focus and magnify the light of more distant galaxies that are often far too faint to see by any other means. “We take advantage of nature’s own telescope,” says Dan Coe, principal investigator of RELICS at the Space Telescope Science Institute in Baltimore.