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"Long before it's in the papers"
January 05, 2010

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Hubble reveals “uncharted” cosmic zone

Jan. 5, 2010
Courtesy Space Telescope Science Institute
and World Science staff

NASA’s Hub­ble Space Tel­e­scope has bro­ken the dis­tance lim­it for ga­lax­ies and un­cov­ered a hith­er­to un­known pri­mor­di­al popula­t­ion of small, ultra-blue ga­lax­ies, as­tro­no­mers say.

The deeper Hub­ble looks in­to space, the far­ther back in time it looks, be­cause light takes time to reach us. This lets as­tro­no­mers see ga­lax­ies as they were 13 bil­lion years ago, they say—a­bout 600 mil­lion to 800 mil­lion years af­ter the “Big Bang” ex­plo­sion be­lieved to have giv­en birth to the un­iverse.

This com­pos­ite im­age com­bin­ing in­fra­red and vis­i­ble light shows ga­lax­ies at an es­ti­mat­ed 700 mil­lion years af­ter the Big Bang (in light blue boxes or cir­cles) and 800 mil­lion years (in dark blue boxes or cir­cles.) (Im­age cour­te­sy Ivo Labbe)
Five in­terna­t­ional teams of as­tro­no­mers have an­a­lyzed da­ta from a new in­fra­red cam­era on Hub­ble, the Wide Field Cam­era 3. Scientists have sub­mit­ted 15 re­search pa­pers and are to pre­sent some early re­sults at the Jan. 6 meet­ing of the Amer­i­can As­tro­nom­i­cal So­ci­e­ty in Wash­ing­ton, D.C.

“With the re­ju­ve­nat­ed Hub­ble and its new in­stru­ments, we are now en­ter­ing un­chart­ed ter­ri­to­ry that is ripe for new dis­cov­er­ies,” said Garth Il­ling­worth of the Un­i­vers­ity of Cal­i­for­nia, San­ta Cruz, lead­er of a sur­vey team. 

“The deepest-ever near-in­fra­red view of the un­iverse—the ‘HUD­F09’ im­age—has now been com­bined with the deep­est-ever op­ti­cal im­age—the orig­i­nal ‘HUDF’ tak­en in 2004—to push back the fron­tiers of the search­es for the first ga­lax­ies.”

Rych­ard Bouwens of the Un­ivers­ity of Cal­i­for­nia, San­ta Cruz, a mem­ber of Illing­worth’s team and lead­er of a pa­per on the prop­er­ties of these ga­lax­ies, said “the faintest ga­lax­ies are now show­ing signs of link­age to their ori­gins from the first stars. They are so blue that they must be ex­tremely de­fi­cient in heavy el­e­ments, thus rep­re­sent­ing a popula­t­ion that has nearly pri­mor­di­al char­ac­ter­is­tics.” Stars con­tain more heavy el­e­ments lat­er in their lives and later in the his­to­ry of the un­iverse.

“These ga­lax­ies could have roots stretch­ing in­to an ear­li­er popula­t­ion of stars. There must be a sub­stan­tial com­po­nent of ga­lax­ies be­yond Hub­ble’s de­tec­tion lim­it,” which should be vi­sible to the more po­wer­ful James Webb Space Tele­scope planned for launch in 2014, said James Dun­lop of the Un­ivers­ity of Ed­in­burgh, U.K. 

The ex­ist­ence of the new­found ga­lax­ies pushes back the time when ga­lax­ies be­gan to form to be­fore 500-600 mil­lion years af­ter the Big Bang, re­search­ers said.

The ob­serva­t­ions al­so dem­on­strate the pro­gres­sive build­up of ga­lax­ies and pro­vide fur­ther sup­port for a “hier­ar­chi­cal” mod­el of gal­axy as­sem­bly, they added. In that mod­el, small ob­jects merge pro­gres­sively to form big­ger ob­jects over time. It’s like streams merg­ing in­to trib­u­tar­ies and then in­to a bay.

“These ga­lax­ies are as small as 1/20th the Milky Way’s di­am­e­ter,” re­ports Pas­cal Oesch of the Swiss Fed­er­al In­sti­tute of Tech­nol­o­gy in Zu­rich. “Yet they are the very build­ing blocks from which the great ga­lax­ies of to­day, like our own Milky Way, ul­ti­mately formed,” ex­plains Mar­cel­la Car­ollo, al­so of the Swiss Fed­er­al In­sti­tute of Tech­nol­o­gy in Zu­rich. Oesch and Car­ollo are mem­bers of Illing­worth’s team.

The new­found ob­jects are cru­cial to un­der­stand­ing the ev­o­lu­tion­ary link be­tween the birth of the first stars, the forma­t­ion of the first ga­lax­ies, and the se­quence of events that re­sulted in the as­sembly of our Milky Way and si­m­i­lar spir­al ga­lax­ies, as­tro­no­mers said.

“To our sur­prise, the re­sults show that these ga­lax­ies at 700 mil­lion years af­ter the Big Bang must have started form­ing stars hun­dreds of mil­lions of years ear­li­er, push­ing back the time of the ear­li­est star forma­t­ion,” said team mem­ber Ivo Labbe of the Car­ne­gie In­sti­tute of Wash­ing­ton, lead­er of two pa­pers on the da­ta from the com­bined NASA Great Ob­ser­va­tories.

A prob­lem with the find­ings, sci­en­tists added, is that it still seems these early ga­lax­ies did­n’t put out enough radia­t­ion to “reion­ize” the early un­iverse by strip­ping elec­trons off the hy­dro­gen that cooled af­ter the Big Bang. This “reion­iz­a­tion” oc­curred be­tween about 400 mil­lion and 900 mil­lion years af­ter the Big Bang, but as­tro­no­mers still don’t know what caused it.

* * *

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NASA’s Hubble Space Telescope has broken the distance limit for galaxies and uncovered a hitherto unknown primordial population of compact, ultra-blue galaxies, astronomers say. The deeper Hubble looks into space, the farther back in time it looks, because light takes time to reach us. This lets astronomers see galaxies as they were 13 billion years ago, they say—about 600 million to 800 million years after the “Big Bang” explosion believed to have given birth to the universe. Data from Hubble’s new infrared camera, the Wide Field Camera 3 have been analyzed by five international teams of astronomers. Fifteen research papers have been submitted and some early results are being presented on Jan. 6 at the meeting of the American Astronomical Society in Washington, D.C. “With the rejuvenated Hubble and its new instruments, we are now entering uncharted territory that is ripe for new discoveries,” said Garth Illingworth of the University of California, Santa Cruz, leader of a survey team. “The deepest-ever near-infrared view of the universe—the ‘HUDF09’ image—has now been combined with the deepest-ever optical image—the original ‘HUDF’ taken in 2004—to push back the frontiers of the searches for the first galaxies.” Rychard Bouwens of the University of California, Santa Cruz, a member of Illingworth’s team and leader of a paper on the properties of these galaxies, said that, “the faintest galaxies are now showing signs of linkage to their origins from the first stars. They are so blue that they must be extremely deficient in heavy elements, thus representing a population that has nearly primordial characteristics.” Stars contain more heavy elements later in their lives or in the history of the universe. “These galaxies could have roots stretching into an earlier population of stars. There must be a substantial component of galaxies beyond Hubble’s detection limit,” said James Dunlop of the University of Edinburgh. Three teams worked to find these new galaxies and did so in a burst of papers immediately after the data were released in September, soon followed by a fourth team, and later a fifth team. The existence of the newfound galaxies pushes back the time when galaxies began to form to before 500-600 million years after the Big Bang, researchers said. The observations also demonstrate the progressive buildup of galaxies and provide further support for a “hierarchical” model of galaxy assembly, they added. In that model, small objects merge progressively to form bigger objects over time. It’s like streams merging into tributaries and then into a bay. “These galaxies are as small as 1/20th the Milky Way’s diameter,” reports Pascal Oesch of the Swiss Federal Institute of Technology in Zurich. “Yet they are the very building blocks from which the great galaxies of today, like our own Milky Way, ultimately formed,” explains Marcella Carollo, also of the Swiss Federal Institute of Technology in Zurich. Oesch and Carollo are members of Illingworth’s team. The newfound objects are crucial to understanding the evolutionary link between the birth of the first stars, the formation of the first galaxies, and the sequence of events that resulted in the assembly of our Milky Way and similar spiral galaxies in today’s universe, astronomers say. The HUDF09 team also combined the new Hubble data with observations from NASA’s Spitzer Space Telescope to estimate the ages and masses of the galaxies. “To our surprise, the results show that these galaxies at 700 million years after the Big Bang must have started forming stars hundreds of millions of years earlier, pushing back the time of the earliest star formation in the universe,” said team member Ivo Labbe of the Carnegie Institute of Washington, leader of two papers on the data from the combined NASA Great Observatories. A problem with the findings, scientists added, is that it still seems these early galaxies didn’t put out enough radiation to “reionize” the early universe by stripping electrons off the hydrogen that cooled after the Big Bang. This “reionization” occurred between about 400 million and 900 million years after the Big Bang, but astronomers still don’t know which light sources caused it.