A glimpse into the universe's oldest galaxies

Astronomers have captured images of primordial galaxies that helped light up the cosmos after the Big Bang.

Beijing, China - A global team of astronomers exploring the origins of the universe has captured images of ancient "starburst" galaxies that helped end the "cosmic dark ages" 13-billion years ago.

Using the world's most advanced orbiting telescope, Hubble Space Telescope, these scientists have discovered first-generation galaxies that lit up the heavens with pyrotechnics of massive stars following the Big Bang. 

Analysing starlight from one faint galaxy - the most distant ever found - astrophysicists determined that its heavily red-shifted photons were nearly as old as the universe itself. Red-shift measures the changing colour or wavelength of light with the expansion of the cosmos and the passage of time.  

These ancient particles of light were emitted by a primordial grouping of stars that emerged some 150 million years after the Big Bang, explained Adi Zitrin, a Hubble scholar in astronomy at the California Institute of Technology who helped find and explore the features of the galaxy, named "MACS0647-JD".

Looking back in time

Scientists were able to pinpoint the age of this early galaxy because of the structure of the cosmos and the properties of light, which together make the universe a massive optical time machine. By scanning the heavens to discover this galaxy, astronomers were also peering more than 100 million centuries back in time.

"We see more distant galaxies as they were in the distant past," said Dan Coe, an astrophysicist at the Space Telescope Science Institute in Baltimore, Maryland, who led the discovery.

To photograph this array of stars, astronomers scattered across four continents - North America, Europe, Asia and South America - and relied primarily on cameras deployed inside the Hubble Space Telescope.

From its position in orbit 500 kilometres above Earth, Hubble avoids the atmospheric distortions faced by ground-based telescopes, and can capture images of some of the most remote collections of stars in the cosmos.

Yet the discovery also relied on supermassive zoom lenses that are built into the structure of the universe. Clusters of galaxies can act as "gravitational lenses" that magnify and brighten background sources of light, including stars and galaxies such as MACS0647-JD. 

This phenomenon was predicted by Albert Einstein more than 100 years ago, while he was refining his theory on how massive bodies such as stars can curve the contours of space-time and deflect waves of light. Gravitational lensing is now being used by astronomers, including Zitrin's group, to peer ever farther across the cosmos and back in time, to the origins of the first galaxies. 

To find the MACS0647-JD galaxy, astronomers used the lens created by the cluster of galaxies called MACS J0647, which magnified and created three identical images of the background collection of stars, said Coe, an expert on gravitational lensing. 

Over the past several years, astronomers including Coe and Zitrin have led the race to pinpoint the clusters that provide the most powerful gravitational lenses in order the find the earliest galaxies at the edges of the known universe. Aided by these cosmic lenses, said Coe, "we have been closing in on the first galaxies".

Ancient galaxies

Another extremely faint galaxy from the young universe was recently discovered by Zitrin's group using a cosmic magnifying lens provided by "Pandora's Cluster", or Abell 2744.  Pandora's Cluster produced multiple images of the ancient background galaxy, which helped astrophysicists date its emergence to roughly 250 million years after the Big Bang, Zitrin explained.

Although it is tiny compared to the spiral expanses of the Milky Way, which is estimated to contain at least 200 billion stars, this ancient galaxy had a far higher star formation rate, or ability to produce new suns relative to its mass, Zitrin said. Both of the high-red-shift galaxies he helped uncover are "representatives of the first generation of galaxies to have formed".

In these ancient, first-generation galaxies, Coe said, "the first primordial stars may have been 100 times the mass of our sun. They burned bright and died young." 

The globe-spanning group of scientists includes several leading researchers based in China. Observation time with the Hubble Space Telescope, which is jointly operated by NASA and the European Space Agency, is open to astronomers around the world.

Finding new pieces in the puzzle of the first galaxies to illuminate the cosmos "is truly a worldwide endeavour involving astronomers of multiple nationalities based around the globe", said Jeremy Lim, a professor at the University of Hong Kong (HKU).

An astrophysicist at the prestigious University of Science and Technology of China, Xingxing Huang, said collaboration on the twin studies of ancient galaxies reflects the increasingly global nature of leading-edge discoveries in astronomy, and he forecast this trend will accelerate in the future.

Zitrin, meanwhile, predicted other massive gravitational lenses spread across the heavens, some of which are now being observed, will likely propel a new wave of discoveries of ancient, distant galaxies.

He added these cosmic zoom lenses work in both directions.

If there were an advanced civilisation in one of the ancient galaxies discovered, its astronomers could likewise use the same gravitational lensing technique to observe our patch of the universe. 

But they would see this sector of the cosmos as it appeared more than 13-billion years ago - perhaps a protogalaxy that would only later expand and evolve into the spiral-shaped disc of the Milky Way.