Hubble Uncovers Tiny Galaxies Bursting with Star Birth in Early Universe

Article ID: 582709

Released: 9-Nov-2011 11:20 AM EST

Source Newsroom: Space Telescope Science Institute (STScI)

  • Credit: NASA, ESA, A. van der Wel (Max Planck Institute for Astronomy, Heidelberg, Germany), H. Ferguson and A. Koekemoer (Space Telescope Science Institute, Baltimore, Md.), and the CANDELS team

    TINY GALAXIES BRIMMING WITH STAR BIRTH. This image reveals 18 tiny galaxies uncovered by NASA's Hubble Space Telescope. The puny galaxies, shown in the postage-stamp-sized images, existed 9 billion years ago and are brimming with star birth. The dwarf galaxies are typically a hundred times less massive than the Milky Way galaxy but are churning out stars at such a furious pace that their stellar content would double in just 10 million years. Hubble's Wide Field Camera 3 and Advanced Camera for Surveys spied the galaxies in the Great Observatories Origins Deep Survey South (GOODS South Deep) field. The galaxies' locations in the GOODS South Deep field are marked by circles in the large image. The galaxies stood out in the Hubble images because the energy from all the new stars caused the oxygen in the gas surrounding them to light up like a bright neon sign. The rapid star birth likely represents an important phase in the formation of dwarf galaxies, the most common galaxy type in the cosmos. The galaxies are among 69 dwarf galaxies found in the GOODS and other fields. Images of the individual galaxies were taken November 2010 to January 2011. The large image showing the locations of the galaxies was taken between September 2002 and December 2004, and between September 2009 and October 2009.

  • Credit: NASA, ESA, A. van der Wel (Max Planck Institute for Astronomy, Heidelberg, Germany), H. Ferguson and A. Koekemoer (Space Telescope Science Institute, Baltimore, Md.), and the CANDELS team

    HUBBLE SPIES TINY GALAXIES AGLOW WITH STAR BIRTH. This image reveals 28 tiny galaxies uncovered by NASA's Hubble Space Telescope. The puny galaxies, shown in the postage-stamp-sized images, existed 9 billion years ago and are brimming with star birth. The dwarf galaxies are typically a hundred times less massive than the Milky Way galaxy but are churning out stars at such a furious pace that their stellar content would double in just 10 million years. Hubble's Wide Field Camera 3 and Advanced Camera for Surveys spied the galaxies in the UKIDSS Ultra Deep Survey field, or UDS (part of the UKIRT Infrared Deep Sky Survey). The galaxies' locations in the UDS field are marked by circles in the large image. The galaxies stood out in the Hubble images because the energy from all the new stars caused the oxygen in the gas surrounding them to light up like a bright neon sign. The rapid star birth likely represents an important phase in the formation of dwarf galaxies, the most common galaxy type in the cosmos. The galaxies are among 69 dwarf galaxies found in the UDS and other fields. The images were made from observations taken between August and December 2010.

  • Credit: NASA, ESA, STScI, and the CANDELS team

    CANDELS DWARF GALAXIES. The CANDELS team identified 69 dwarf galaxies that are undergoing intense bursts of star formation. The dwarf galaxies were found in two regions of the sky called the Great Observatories Deep Survey-South and the UKIDSS Ultra Deep Survey (part of the UKIRT Infrared Deep Sky Survey). Each dwarf is shown centered in cutouts made from near-infrared (I, J, and H band) images acquired by Hubble's Wide Field Camera 3 and Advanced Camera for Surveys. The light from these galaxies has been traveling for about 9 billion years. Many of the stars in nearby dwarf galaxies may have formed in similar starbursts around the same time. The background shows a wider near-infrared view of the CANDELS Ultra Deep Survey field.

Newswise — Using its near-infrared vision to peer 9 billion years back in time, NASA's Hubble Space Telescope has uncovered an extraordinary population of tiny, young galaxies that are brimming with star formation. The galaxies are typically a hundred times less massive than the Milky Way galaxy, yet they churn out stars at such a furious pace that their stellar content would double in just 10 million years. By comparison, the Milky Way would take a thousand times longer to double its population.

These newly discovered dwarf galaxies are extreme even for the young universe, when most galaxies were forming stars at higher rates than they are today. The universe is 13.7 billion years old. Hubble spotted the galaxies because the radiation from young, hot stars has caused the oxygen in the gas surrounding them to light up like a bright neon sign. The rapid star birth likely represents an important phase in the formation of dwarf galaxies, the most common galaxy type in the cosmos.

"The galaxies have been there all along, but up until recently astronomers have been able only to survey tiny patches of sky at the sensitivities necessary to detect them," said Arjen van der Wel of the Max Planck Institute for Astronomy in Heidelberg, Germany. Van der Wel is the lead author of a paper that will be published online Nov. 14 in The Astrophysical Journal. "We weren't looking specifically for these galaxies, but they stood out because of their unusual colors."

The observations were part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS), an ambitious three-year survey to analyze the most distant galaxies in the universe. CANDELS is the census of dwarf galaxies at such an early epoch in the universe's history.

"In addition to the images, Hubble has captured spectra that show us the oxygen in a handful of galaxies and confirm their extreme star-forming nature," said co-author Amber Straughn at NASA's Goddard Space Flight Center in Greenbelt, Md. "Spectra are like fingerprints--they tell us the galaxies' chemical composition."

The observations are somewhat at odds with recent detailed studies of the dwarf galaxies that are orbiting as satellites of the Milky Way.

"Those studies suggest that star formation was a relatively slow process, stretching out over billions of years," explained Harry Ferguson of the Space Telescope Science Institute (STScI) in Baltimore, Md., co-leader of the CANDELS survey. "The CANDELS finding that there were galaxies of roughly the same size forming stars at very rapid rates at early times is forcing us to re-examine what we thought we knew about dwarf galaxy evolution."

Added team member Anton Koekemoer, also of STScI, who is producing all the Hubble imaging data for the survey: "As our observations continue, we should find many more of these young galaxies and gather more details on their star-forming histories."

The CANDELS team uncovered the 69 young dwarf galaxies in near-infrared images taken with Hubble's Wide Field Camera 3 and Advanced Camera for Surveys. The galaxies were found in two regions of the sky called the Great Observatories Origins Deep Survey South and the UKIDSS Ultra Deep Survey (part of the UKIRT Infrared Deep Sky Survey).

The observations suggest that the newly discovered galaxies were very common 9 billion years ago. It is a mystery, however, why the newly found dwarf galaxies were making batches of stars at such a high rate. Computer simulations show that star formation in small galaxies may be episodic. Gas cools and collapses to form stars. The stars then reheat the gas through, for example, supernova explosions, which blow the gas away. After some time, the gas cools and collapses again, producing a new burst of star formation, continuing the cycle.

"While these theoretical predictions may provide hints to explain the star formation in these newly discovered galaxies, the observed 'bursts' are much more intense than what the simulations can reproduce," van der Wel said.

The James Webb Space Telescope, an infrared observatory scheduled to launch later this decade, will be able to probe these faint galaxies at an even earlier era to see the glow of the first generation of stars, providing detailed information of the galaxies' chemical composition.

"With Webb, we'll probably see even more of these galaxies, perhaps even pristine galaxies that are experiencing their first episode of star formation," Ferguson said. "Being able to probe down to dwarf galaxies in the early universe will help us understand the formation of the first stars and galaxies."

For images and more information about Hubble and the CANDELS results, visit:

http://hubblesite.org/news/2011/31
http://www.nasa.gov/hubble
http://www.spacetelescope.org/news/heic1117

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI) conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc. in Washington, D.C.


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