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Astronomers peer into primordial “fog”

Oct. 21, 2010
Courtesy of the European Southern Observatory
and World Science staff

As­tro­no­mers say they have con­firmed the discovery of the fur­thest gal­axy known, an ob­ject so re­mote that it comes from a time when fog shrouded the uni­verse.

An im­age from a sci­en­tif­ic sim­u­la­tion of the "era of re­ion­iz­ation," a pe­ri­od dur­ing which ear­ly ga­lax­ies are be­lieved to have blast­ed away a fog left over from the birth of the uni­verse. (Cour­te­sy M. Al­varez, R. Kaehler, and T. Abel )
“This is the first time we know for sure that we are look­ing at one of the ga­lax­ies that cleared out the fog which had filled the very early Uni­verse,” said Ni­cole Nes­vadba of the In­sti­tute of Space As­t­ro­phys­ics in Par­is. She is a co-au­thor of a pa­per on the find­ings pub­lished in the Oct. 21 is­sue of the re­search jour­nal Na­ture.

Be­cause light takes time to reach us, ex­tremely dis­tant ob­jects are seen as they were long ago, when their light left them. 

The gal­axy is thought to come from a time rel­a­tively soon af­ter the “Big Bang” event that gave birth to the cos­mos. In this early age, as­tro­no­mers be­lieve a dense fog of hy­dro­gen gas per­me­at­ed the uni­verse, a sort of left­o­ver haze from that pri­mor­di­al blast. The first ga­lax­ies blew away this fog with the pow­er­ful light that they emit­ted.

The gal­axy in ques­tion is being seen as it was when the uni­verse was an esti­mated 600 mil­lion years old, about 4 per­cent of its present age, re­search­ers said. Stud­y­ing such ga­lax­ies is ex­tremely hard, they added, be­cause they look faint and ti­ny in the dis­tance; the “fog” does­n’t help.

The team of Eu­ro­pe­an as­tro­no­mers zoned in on the ob­ject us­ing the Eu­ro­pe­an South­ern Ob­ser­va­to­ry’s Very Large Tel­e­scope in Paranal, Chil­e, and ex­am­in­ing can­di­date ga­lax­ies ear­li­er iden­ti­fied by NASA’s Hub­ble Space Tel­e­scope. 

“We did a quick cal­cula­t­ion,” said Matt Lehn­ert of the Par­is Ob­serv­a­to­ry, lead au­thor of the pa­per, “and were ex­cit­ed to find that the im­mense light col­lect­ing pow­er” of the Very Large Tel­e­scope, com­bined with the sen­si­ti­vity of its in­stru­menta­t­ion, “and a very long ex­po­sure time might just al­low us to de­tect the ex­tremely faint glow from one of these re­mote ga­lax­ies and to meas­ure its dis­tance.”

Af­ter two months of anal­y­sis and test­ing, the team con­clud­ed that they had de­tected the faint glow of hy­dro­gen at a “red­shift” of 8.6. Red­shift is a meas­ure of how much the light from a giv­en ob­ject has been stretched due to the on­go­ing ex­pan­sion of the uni­verse as it trav­eled to Earth. This in turn re­veals the dis­tance and age of the ob­ject. 

One of the sur­pris­ing things is that the glow from the gal­axy, dubbed UDFy-38135539, seems not to be strong enough on its own to clear out the hy­dro­gen fog, ac­cord­ing to as­tro­no­mers. “There must be oth­er ga­lax­ies, probably faint­er and less mas­sive near­by com­pan­ions… which al­so helped make the space around the gal­axy trans­par­en­t,” said co-au­thor Mark Swin­bank of Dur­ham Uni­vers­ity in the U.K. “With­out this ad­di­tion­al help the light from the gal­axy, no mat­ter how bril­liant, would have been trapped in the sur­round­ing hy­dro­gen fog and we would not have been able to de­tect it.” 

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Astronomers are reporting that they have measured the distance to the furthest galaxy known, an object so remote that it comes from a time when fog shrouded the universe. Because light takes time to move, extremely distant objects are seen as they were long ago, when their light left them. “This is the first time we know for sure that we are looking at one of the galaxies that cleared out the fog which had filled the very early Universe,” said Nicole Nesvadba of the Institute of Space Astrophysics in Paris, a co-author of a paper reporting the results in the Oct. 21 issue of the research journal Nature. The galaxy is thought to come from a time relatively soon after the “Big Bang” event that gave birth to the cosmos. In this early age, astronomers believe a dense fog of hydrogen gas permeated the universe, a sort of leftover haze from that primordial blast. The first galaxies blew away this fog with the powerful light that they emitted. The galaxy in question is one of these objects, seen as it was when the universe was about 600 million years old, researchers said. Studying such galaxies is extremely hard, they added, because they look faint and tiny to us, and the “fog” doesn’t help. The team of European astronomers zoned in on the object using the European Southern Observatory’s Very Large Telescope in Paranal, Chile, and examining candidate galaxies earlier identified by NASA’s Hubble Space Telescope. “We did a quick calculation,” said Matt Lehnert of the Paris Observatory, lead author of the paper, “and were excited to find that the immense light collecting power” of the Very Large Telescope, combined with the sensitivity of its instrumentation, “and a very long exposure time might just allow us to detect the extremely faint glow from one of these remote galaxies and to measure its distance.” After two months of analysis and testing, the team concluded that they had detected the faint glow of hydrogen at a “redshift” of 8.6. Redshift is a measure of how much the light from a given object has been stretched due to the ongoing expansion of the universe as it traveled to Earth. This in turn reveals the distance and age of the object. One of the surprising things is that the glow from the galaxy, UDFy-38135539, seems not to be strong enough on its own to clear out the hydrogen fog, according to astronomers. “There must be other galaxies, probably fainter and less massive nearby companions… which also helped make the space around the galaxy transparent,” said co-author Mark Swinbank of Durham University in the U.K. “Without this additional help the light from the galaxy, no matter how brilliant, would have been trapped in the surrounding hydrogen fog and we would not have been able to detect it.”