Hubble finds the oldest stars in the universe

The Hubble space telescope has photographed the oldest stars ever discovered in the universe - dating as far back as 13.2 billion years.

Astronomers believe that the discovery will help us learn about the formation of our own galaxy. The universe is currently believed to have originated 13.7billion years ago, with the Big Bang, meaning that these galaxies were formed in the first 500million years of the universe's existence.

For comparison, the Solar System and its planets, including Earth, was formed 4.6billion years ago.

The Hubble telescope was able to see the ancient galaxies thanks to a particular property of light travelling interstellar distances - as it passes large galaxy clusters, the light bends slightly. This means that large galaxy clusters, which exert an enormous gravitational pull, can be used like a lens to focus on objects behind them that are much further away.

In this case, Hubble focused on two clusters of galaxies - Abell 2744 and Abell 1689 - to peer into the distant past of the universe. The images of the clusters, which lie in the Sculptor and Ursa Major constellations respectively, contain 58 hitherto unseen galaxies.

The gravitational focussing makes objects behind Abell 2744 and 1689 appear between ten and twenty times larger than they actually are.

The early galaxies can be identified by a phenomenon known as 'redshift', whereby the light given off by an object appears more red the futher away and faster away they are moving from Earth. In this case, we are seeing them as they appeared 13.2billion years ago.

"These just stuck out like a sore thumb because they are far brighter than we anticipated," explained astronomer Garth Illingworth of the University of California at Santa Cruz. "There are strange things happening regardless of what these sources are. We're suddenly seeing luminous, massive galaxies quickly build up at such an early time. This was quite unexpected."



The galaxies are smaller and fainter than any previously seen - up to twenty times smaller than the Milky Way. However, due to their age, they would have produced stars at a greater rate, and may have contained a billion stars each.

"There's always been a concern that we've only found the brightest of the distant galaxies," said Brian Siana of the University of California at Riverside. "The bright galaxies, however, represent the tip of the iceberg. We believe most of the stars forming in the early universe are occurring in galaxies we normally can't see at all. Now we have found those 'unseen' galaxies, and we're really confident that we're seeing the rest of the iceberg."

The images are part of a series from Hubble called Frontier Fields, and show galaxies 500million years older than any previously imaged. They were presented at the American Astronomical Society meeting in Washington D.C.