NASA's Hubble achieves deepest cosmic view yet

Using NASA's Hubble Space Telescope, astronomers uncovered a previously unseen population of seven primitive galaxies that formed more than 13 billion years ago, when the universe was less than 4 per cent of its present age.

The deepest images to date from Hubble yield the first statistically robust sample of galaxies that tells how abundant they were close to the era when galaxies first formed, NASA said in a statement.

The results are from an ambitious Hubble survey of an intensively studied patch of sky known as the Ultra Deep Field (UDF).

A team of astronomers led by Richard Ellis of the California Institute of Technology used Hubble's Wide Field Camera 3 (WFC 3) to peer deeper into space in near-infrared light than any previous Hubble observation.

The results show a smooth decline in the number of galaxies looking back in time to about 450 million years after the big bang.

The observations support the idea galaxies assembled continuously over time and also may have provided enough radiation to reheat, or re-ionise, the universe a few hundred million years after the theorised big bang.

Looking deeper into the universe also means peering further back in time. The universe is estimated to be 13.7 billion years old. The newly discovered galaxies are seen as they looked 350 to 600 million years after the big bang. Their light is just arriving at Earth now.

Astronomers study the distant universe in near-infrared light because the expansion of space stretches ultraviolet and visible light from galaxies into infrared wavelengths, a phenomenon called "redshift." The more distant a galaxy, the higher its redshift.

The greater depth of the new Hubble images, together with a carefully designed survey strategy, allows this work to go further than previous studies, thereby providing what researchers say is the first reliable census of this epoch.

Notably, one of the galaxies may be a distance record breaker, observed 380 million years after the birth of our universe in the big bang, corresponding to a redshift of 11.9.

"Our study has taken the subject forward in two ways. First, we have used Hubble to make longer exposures. The added depth is essential to reliably probe the early period of cosmic history. Second, we have used Hubble's available colour filters very effectively to more precisely measure galaxy distances," Ellis said.