La galassia più lontana, 13 miliardi di anni luce da noi!

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Da Space.com

Most Distant Galaxy Hints at Dark Ages

By Robert Roy Britt
Senior Science Writer
posted: 07:00 am ET
16 February 2004

Astronomers seeking to glimpse the very beginnings of the universe announced this weekend they may have spotted the most distant galaxy yet, one that could shed light on the end of the so-called Dark Ages of cosmology that preceded the well-lit universe we know today.

The scientists are unsure of the exact distance to the galaxy but know it is near the limit of what can be found with current telescopes. It is estimated to be 13 billion light-years away, seen at a time when the universe was just 700 million to 750 million years old.

Unlike other distance records in recent years, mostly coming out of the Sloan Digital Sky Survey, this one was a product of the Hubble Space Telescope and the W. M. Keck Observatory in Hawaii.

Jean-Paul Kneib, of Caltech and the Observatoire Midi-Pyrénées, led the work.

Running away

The distance to faraway galaxies is measured by noting how rapidly they are moving away from our own. Because the universe is expanding at an ever-increasing pace, all widely dispersed galaxies retreat from each other at greater speeds the farther apart they are.

Scientists measure all this by noting a galaxy's redshift, the extent to which the wavelengths of its light have been stretched toward the red end of the spectrum during its long travels across the cosmos.

The previous record holder, a Sloan galaxy, is at redshift 6.4.

The newfound galaxy has a redshift of at least 6.6, based on the Hubble imaging, and may be near 7.0 according to a less firm analysis of the Keck observations.

The universe is now about 13.7 billion years old.

Unusual properties of the galaxy could shed light on the end of a theorized era of cosmic time called the Dark Ages. During the Dark Ages, shortly after the Big Bang, hydrogen atoms had gathered to form the first stars, but they had yet to condense and ignite into the thermonuclear furnaces that create light. Scientists don't yet know how long the era lasted.

Unusual properties

The newly spotted galaxy appears not to have a bright emission from hydrogen that is seen in many other faraway galaxies. Further, its intense ultraviolet signal is much stronger than what's seen in more modern galaxies that are undergoing rapid star formation. That suggests the most distant known galaxy may contain mostly massive stars, which is in line with what theorists expect from the first galaxies.

"The unusual properties of this distant source are very tantalizing because, if verified by further study, they could represent those expected for young stellar systems that ended the dark ages," said Richard Ellis, a Caltech astronomer and coauthor of an article on the discovery that will be published in the Astrophysical Journal. He presented the finding today at a meeting in Seattle of the American Association for the Advancement of Science.

The discovery was not routine. It involved a trick of light provided by a natural magnifying glass in the heavens.

The primeval galaxy is situated behind a more nearby cluster of galaxies, called Abell 2218. The tremendous gravity of the galaxy grouping bends and amplifies light from the more distant object as it passes through the cluster. The technique, known as gravitational lensing, has been used to spot other object in the early universe.

"We are looking at the first evidence of our ancestors on the evolutionary tree of the entire universe," said Frederic Chaffee, director of the Keck Observatory.

Near the limit

Scientists have been saying for a few years now that they are closing in on the Big Bang with each record-setter. But each new benchmark is now an incremental improvement and increasingly difficult to top.

In a separate talk at the meeting, Xiaohui Fan of the University of Arizona's Steward Observatory in Tucson, discussed the limits of today's telescopes in spotting objects in the primordial universe. Fan was part of the Sloan team that found the previous record-holder.

These distant galaxies are called quasars, short for quasi-stellar radio sources. They were first noticed in the 1950s and '60s and were thought to be nearby stars that behaved strangely.

Current telescopes cannot routinely find quasars beyond redshift 6.5, Fan said. To reach redshift 10 or greater, and peer into the Dark Ages, will require the power of the James Web Space Telescope, due to launch early in the next decade.

There is a lot to learn.

When it was born, the universe contained only hydrogen and helium. All other elements were forged inside stars and in the explosive deaths of the most massive stars, known as supernovas.

"But we see a lot of other elements around those early quasars," Fan said. "We see evidence of carbon, nitrogen, iron and other elements, and it's not clear how these elements got there. There is as much iron, proportionate to the population of those early systems, as there is in mature galaxies nearby."

Theorists have become increasingly impressed with how rapidly stars must have formed as the Dark Ages ended.

[ominiverdi]

Originariamente inviato da LittleLux
Non credo proprio, anche perchè sarebbe fisicamente impossibile, probabilmente quel 7 sta ad indicare lo spostamento verso il rosso dell'oggetto in esame (la nostra galassia distante 13 mld. di anni luce), rispetto allo spostamento verso il rosso dello spettro di una sorgente presa a campione.

Ciao

infatti, sull' atlante che ho (vecchiotto) e' stimato che al max possono allontanarsi a velocita' prossime a quelle della luce