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Last Updated: Sunday, 15 February, 2004, 17:09 GMT
Hubble sees 'most distant object'
By Jonathan Amos
BBC News Online science staff, in Seattle

Abell 2218 magnifies the new object by a factor of 25

The farthest object in the Universe yet detected has been seen by scientists using the Hubble and Keck telescopes.

It is so distant its light must have set out when the Universe was just 750m years old to reach the Earth now.

Details of the discovery were revealed by a team of astrophysicists from the California Institute of Technology.

They said the work underlined again the remarkable capabilities of Hubble and called on Nasa to reverse its decision to stop servicing the telescope.

The US space agency has confirmed it will not send another shuttle to upgrade the space telescope, which probably means Hubble has no more than three years of full observations ahead of it.

"We need Hubble... we could not have made this discovery without it," said Caltech's Richard Ellis, who was explaining his institute's latest work at the annual meeting of the American Association for the Advancement of Science here in Washington State.

"One of the instruments that would be placed on the telescope is a new infrared camera which would be perfect for the work we want to do.

"Many of us hope the decision to abandon further visits to Hubble will be examined very carefully because the scientific potential is very great."

Cosmic history

The new object was first seen in a series of observations of a cluster of galaxies known as Abell 2218, conducted with Hubble's Advanced Camera for Surveys, installed on its last servicing mission.

It is forming stars prodigiously and is a very energetic source, so it may be an example of an object from that early time
Richard Ellis,
The object is not in the cluster but situated a long way behind it. Abell 2218 was simply used as a "gravitational lens" - a massive foreground object that can bend and magnify the light of objects much further away.

Gravitational lensing is a remarkable astronomical trick, first predicted by Einstein, that allows scientists to probe regions of the Universe that are estimated to be 13bn light-years away - to look back in time to when some of the very first stars were shining.

The Hubble images were analysed to work out the new object's redshift, which measures the degree to which its light is being stretched by the expansion of the Universe.

The greater the redshift, the more distant the object and the earlier it is being seen in cosmic history.

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The Hubble data suggested a redshift of 6.6, but follow-up observations with the 10-metre Keck telescopes on Hawaii indicated the new object probably has a redshift closer to 7.0 - a record.

"The new object is a small and compact system of stars," said Professor Ellis. "It's about 2,000 light-years across; our own galaxy by comparison is about 60,000 light-years across.

"It is forming stars prodigiously and is a very energetic source, so it may be an example of an object from that early time [just after the "Dark Ages"] that is the first of its kind to form in the Universe."

The term "Dark Ages" was coined by the English Astronomer Royal, Sir Martin Rees, to signify the period in cosmic history when hydrogen atoms first formed but stars had not yet had the opportunity to condense and ignite.

Nobody is quite clear how long this phase lasted, and the detailed study of the cosmic sources that brought this period to an end is a major goal of modern cosmology.

The latest discovery has been written up for a forthcoming paper in the Astrophysical Journal. The lead author is Caltech astronomer Jean-Paul Kneib.

Richard Ellis, California Institute of Technology
"We think we found the most distant object currently known"


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