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Hubble peers back to an age of fewer, newer galaxies

Jan. 16, 2011
Courtesy of UCSC
and World Science staff

As­tro­no­mers us­ing the Hub­ble Space Tel­e­scope have peered so far across space that they have seen an age when ga­lax­ies were much few­er and fur­ther apart than to­day, a new re­port said.

The sci­en­tists stu­dy­ing ultra-deep im­ag­ing da­ta from the in­stru­ment found what they said may be the most dis­tant gal­axy ev­er seen, about 13.2 bil­lion light-years away. A light-year is the dis­tance light trav­els in a year. Be­cause light takes time to trav­el, view­ing things at such a dis­tance means they are be­ing seen as they looked just that many years ago.

A gal­axy be­lieved to have ex­isted 480 mil­lion years af­ter the Big Bang, shown in the blue box at up­per left and en­larged in the blue box at low­er right. (Cred­it: NA­SA, ESA, Garth Illing­worth (U­ni­ver­si­ty of Cal­i­for­nia, San­ta Cruz) and Rych­ard Bou­w­ens (U­ni­ver­si­ty of Cal­i­for­nia, San­ta Cruz and Lei­den Uni­ver­si­ty) and the HUD­F09 Team)
The study pushed the lim­its of Hub­ble’s ca­pa­bil­i­ties, as­tro­no­mers said—extending its reach back to about 480 mil­lion years af­ter the “Big Bang” event that gave birth to our uni­verse. The uni­verse then was just 4 per­cent of its cur­rent age. 

“We’re get­ting back very close to the first ga­lax­ies, which we think formed around 200 to 300 mil­lion years af­ter the Big Bang,” said Garth Illing­worth of the Uni­vers­ity of Cal­i­for­nia, San­ta Cruz, who led the study with fel­low as­tron­o­mer Rych­ard Bouwens, now at Lei­den Uni­vers­ity in the Neth­er­lands. The find­ings are to be pub­lished in the Jan. 27 is­sue of the re­search jour­nal Na­ture. 

Us­ing in­fra­red light da­ta gath­ered by an in­stru­ment mount­ed on Hub­ble known as the Wide Field Plan­e­tary Cam­era 3, the as­tro­no­mers said they saw dra­mat­ic changes in ga­lax­ies over a pe­ri­od from about 480 to 650 mil­lion years af­ter the Big Bang. The rate of star birth in the uni­verse in­creased by ten times dur­ing this 170 mil­lion-year pe­ri­od, Illing­worth said.

“This is an as­ton­ish­ing in­crease in such a short pe­ri­od, just one per­cent of the cur­rent age of the uni­verse,” he said.

There were al­so strik­ing changes in the num­bers of ga­lax­ies de­tected. “Our pre­vi­ous searches had found 47 ga­lax­ies at some­what lat­er times when the uni­verse was about 650 mil­lion years old. Howev­er, we could only find one gal­axy can­di­date just 170 mil­lion years ear­lier,” Illing­worth said. “The uni­verse was chang­ing very quickly in a short amount of time.” 

Ac­cord­ing to Bouwens, these find­ings are con­sist­ent with the “hier­ar­chi­cal” pic­ture of gal­axy forma­t­ion. This is a mod­el that pro­poses that ga­lax­ies grew and merged un­der the gravita­t­ional in­flu­ence of an in­vis­i­ble sub­stance known as dark mat­ter, which is de­tect­a­ble only through its gravita­t­ional ef­fects.

“We see a very rap­id build-up of ga­lax­ies around this time,” Illing­worth said. “For the first time now, we can make real­is­tic state­ments about how the gal­axy popula­t­ion changed dur­ing this pe­ri­od and pro­vide mean­ing­ful con­straints for mod­els of gal­axy forma­t­ion.” 

As­tro­no­mers gauge the dis­tance of an ob­ject from its red­shift, a meas­ure of how much the on­go­ing ex­pan­sion of space has stretched the light. This stretch gives it a more red­dish col­or. The newly de­tected gal­axy has an es­ti­mat­ed red­shift of 10.3, which cor­re­sponds to an est­im­ated time of 13.2 bil­lion years ago.

“This re­sult is on the edge of our ca­pa­bil­i­ties, but we spent months do­ing tests to con­firm it, so we now feel pret­ty con­fi­den­t,” Illing­worth said.

The gal­axy, a faint smudge of star­light in the Hub­ble im­ages, is ti­ny com­pared to the mas­sive ga­lax­ies seen in the lo­cal uni­verse. Our own Milky Way, for ex­am­ple, is more than 100 times larg­er. The re­search­ers al­so de­scribed three oth­er ga­lax­ies with red­shifts great­er than 8.3. 

The study in­volved a thor­ough search of da­ta col­lect­ed from deep im­ag­ing of the Hub­ble Ul­tra Deep Field, a small patch of sky about one-tenth the size of the Moon. Dur­ing two four-day stretches in sum­mer 2009 and sum­mer 2010, Hub­ble fo­cused on one ti­ny spot in the field for a to­tal ex­po­sure of 87 hours with the in­fra­red cam­era.

To go be­yond red­shift 10, as­tro­no­mers will have to wait for Hub­ble’s suc­ces­sor, the James Webb Space Tel­e­scope, which NASA plans to launch lat­er this dec­ade. That tele­scope should al­so be able to per­form the meas­urements needed to con­firm the re­ported gal­axy at red­shift 10, the in­ves­ti­gat­ors said.

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Astronomers using the Hubble Space Telescope have peered so far across space that they have seen an age when galaxies were much fewer and further apart than today, a new report said. The scientists studying ultra-deep imaging data from the instrument found what they said may be the most distant galaxy ever seen, about 13.2 billion light-years away. A light-year is the distance light travels in a year. Because light takes time to travel, viewing things at such a distance means they are being seen as they looked just that many years ago. The study pushed the limits of Hubble’s capabilities, astronomers said—extending its reach back to about 480 million years after the “Big Bang” event that gave birth to our universe. The universe then was just 4 percent of its current age. “We’re getting back very close to the first galaxies, which we think formed around 200 to 300 million years after the Big Bang,” said Garth Illingworth of the University of California, Santa Cruz, who led the study with fellow astronomer Rychard Bouwens, now at Leiden University in the Netherlands. The findings are to be published in the Jan. 27 issue of the research journal Nature. Using infrared light data gathered by an instrument mounted on Hubble known as the Wide Field Planetary Camera 3, the astronomers said they saw dramatic changes in galaxies over a period from about 480 to 650 million years after the Big Bang. The rate of star birth in the universe increased by ten times during this 170 million-year period, Illingworth said. “This is an astonishing increase in such a short period, just one percent of the current age of the universe,” he said. There were also striking changes in the numbers of galaxies detected. “Our previous searches had found 47 galaxies at somewhat later times when the universe was about 650 million years old. However, we could only find one galaxy candidate just 170 million years earlier,” Illingworth said. “The universe was changing very quickly in a short amount of time.” According to Bouwens, these findings are consistent with the “hierarchical” picture of galaxy formation. This is a model that proposes that galaxies grew and merged under the gravitational influence of an invisible substance known as dark matter, which is detectable only through its gravitational effects. “We see a very rapid build-up of galaxies around this time,” Illingworth said. “For the first time now, we can make realistic statements about how the galaxy population changed during this period and provide meaningful constraints for models of galaxy formation.” Astronomers gauge the distance of an object from its redshift, a measure of how much the ongoing expansion of space has stretched the light, giving it a more reddish color. The newly detected galaxy has an estimated redshift of 10.3, which corresponds to an object that emitted the light we now see 13.2 billion years ago. “This result is on the edge of our capabilities, but we spent months doing tests to confirm it, so we now feel pretty confident,” Illingworth said. The galaxy, a faint smudge of starlight in the Hubble images, is tiny compared to the massive galaxies seen in the local universe. Our own Milky Way, for example, is more than 100 times larger. The researchers also described three other galaxies with redshifts greater than 8.3. The study involved a thorough search of data collected from deep imaging of the Hubble Ultra Deep Field, a small patch of sky about one-tenth the size of the Moon. During two four-day stretches in summer 2009 and summer 2010, Hubble focused on one tiny spot in the field for a total exposure of 87 hours with the infrared camera. To go beyond redshift 10, astronomers will have to wait for Hubble’s successor, the James Webb Space Telescope, which NASA plans to launch later this decade. JWST will also be able to perform the spectroscopic measurements needed to confirm the reported galaxy at redshift 10.