Science & Environment

Hubble Space Telescope achieves deepest cosmic view yet

Image caption Objects like UDFj-39546284 are at the limit of the Hubble telescope's vision

Hubble astronomers have observed deeper into space than ever before.

In doing so, they have identified six new galaxies of stars that formed just a few hundred million years after the Big Bang itself.

The study also updates a distance estimate for a seventh galaxy, placing it further back in time than any object previously identified.

Called UDFj-39546284, this is seen when the cosmos was less than 3% of its current age.

The new Hubble telescope investigation was led by Richard Ellis from the California Institute of Technology (Caltech) and colleagues at Edinburgh University, Jim Dunlop and Ross McLure.

Its significance is that it gives us the clearest insight into how some of the earliest years of cosmic history unfolded.

The data supports the notion that the first galaxies assembled their constituent stars in a smooth fashion - not in some sudden burst.

"Of course, the most distant object is interesting, but it's the census - the seven objects - that gives us the first indication of the population of objects in the heart of this… era," said Prof Ellis.

"If you compare the number of galaxies that we see to the abundance of objects once the Universe had expanded a little bit, we describe a very smooth decline in the number of objects as we go back into cosmic history," he told reporters.

The new results stem from a project called UDF12 and centre on a tiny patch of sky in the Constellation Fornax (The Furnace).

This is the location where Hubble has repeatedly stared since 2003, trying to build up a picture of objects whose separation from us is so great that their light arrives in dribs and drabs.

Ellis's and colleagues' work adds more than 100 hours of observations to this extraordinary Ultra Deep Field imagery - one of Hubble's greatest accomplishments.

Image caption The positions of the seven galaxies in the Hubble Ultra Deep Field, a patch of sky one-tenth the diameter of the full Moon. Their redshifts ("z") are indicated. One object (z=11.9) is likely a record-breaker

The light being seen from the remotest objects in the UDF would have started out as short wavelength (ultraviolet) emission that was then subsequently stretched to longer (infrared) wavelengths by the expansion of the Universe. And because it has taken so long for this light to reach us, the observations are effectively looking back in time.

This is difficult work, however. By the time the "redshifted" light lands on Hubble's powerful Wide Field Camera 3 instrument, it has been stretched to the very edge of what is detectable by this equipment.

Nonetheless, the team believes the data is robust enough to certify the six new galaxies and the one re-classification.

The objects lie in a range that covers redshifts 8.2-11.9 - the technical way of describing a period in time that runs from about 600 million years to 380 million years after the Big Bang (current cosmology suggests the Big Bang occurred some 13.77 billion years ago).

The most distant object, UDFj-39546284, was first announced by Garth Illingworth and Rychard Bouwens in a Nature paper in 2011. They gave it a redshift of 10 (480 million years after the Big Bang).

But the improved and extended dataset from Prof Ellis's group strongly suggests this galaxy really lies at an even greater distance. Either that or it has properties in its light emission that hitherto have never been noted in a closer object.

Scientists are very keen to probe these colossal separations in time and distance because they will learn how the early Universe grew its structures, and that in turn will help them explain why the cosmos looks the way it does now.

In particular, they want to see more evidence for the very first populations of stars. These hot giants would have grown out of the cold neutral gas that pervaded the young cosmos.

These behemoths would have burnt brilliant but brief lives, producing the very first heavy elements.

They would also have "fried" the neutral gas around them - ripping electrons off atoms - to produce the diffuse intergalactic plasma we still detect between nearby stars today.

"When we look at the properties of the six new galaxies at redshifts eight and nine - they already seem reasonably mature," Prof Dunlop from Edinburgh's Institute of Astronomy told BBC News.

"They've already got a reasonable amount of heavy elements from previous generations of stars.

Image caption Edinburgh University's Ross Mclure and Jim Dunlop helped design the new Hubble survey

"So, in a way, the take home message is that we're still not seeing the first generation of stars - the so-called Population III stars. Even when we push to less than what is now 5% of the age of the Universe; we're still seeing second-generation, relatively evolved objects."

John Grunsfeld, Nasa's associate administrator for science and the astronaut known as the "Hubble repair man" because of the number of servicing missions he flew to the telescope, commented on the latest research: "These are baby pictures of the Universe," he told reporters.

"These images are giving us the tantalizing view of what happened in the very earliest stages of the Universe. This is the time when the Universe was filled with hydrogen and starts to make stars and galaxies that make the chemical elements that we are primarily made out of - the oxygen we breathe, the iron in our blood, the calcium in our bones."

Going even deeper in time is going to be extremely difficult with Hubble. This will likely have to wait for its successor, the James Webb Space Telescope (JWST), due for launch in 2018.

JWST will have a bigger mirror and more capability in the infrared regions where the light from the very first objects is expected to be found.

What Hubble can do, however, is broaden its search, conducting deep field observations in other places on the sky. This will provide more reliable statistics on early populations, giving astronomers reassurance that the Fornax UDF does not represent some sort of cosmic quirk.

Scholarly papers describing the Ellis group's work are being published in Astrophysical Journal Letters.

Looking back in time with the Hubble Space Telescope

  • Period before the first stars switch on is known as the 'Dark Ages'
  • The cosmos at this stage is dominated by neutral hydrogen gas
  • First stars forge the first heavy elements and 'fry' the gas around them
  • Epoch of "First Light" is a key epoch for cosmic evolution and follow me on Twitter: @BBCAmos

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