Hubble Uncovers Tiny Galaxies Bursting With Starbirth in Early Universe
ScienceDaily (Nov. 10, 2011) — Using its infrared vision to peer nine billion years back in time, the NASA/ESA Hubble Space Telescope has uncovered an extraordinary population of tiny, young galaxies that are brimming with star formation.
This image reveals 18 tiny galaxies uncovered by the NASA/ESA 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 population would double in just 10 million years. (Credit: This image reveals 18 tiny galaxies uncovered by the NASA/ESA 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 population would double in just 10 million years. Hubble’s Wide Field Camera 3 and Advanced Camera for Surveys spied the galaxies in a field called the Great Observatories Origins Deep Survey (GOODS). The galaxies' locations in the GOODS field are marked 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 fluorescent 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 location 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), H. Ferguson and A. Koekemoer (Space Telescope Science Institute), and the CANDELS team)
The galaxies are churning out stars at such a rate that the number of stars in them would double in just ten million years. For comparison, the Milky Way has taken a thousand times longer to double its stellar population.
These newly discovered dwarf galaxies are around a hundred times smaller than the Milky Way. Their star formation rates are extremely high, even for the young Universe, when most galaxies were forming stars at higher rates than they are today. They have turned up in the Hubble images because the radiation from young, hot stars has caused the oxygen in the gas surrounding them to light up like a fluorescent sign.
Astronomers believe this rapid starbirth 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," says Arjen van der Wel of the Max Planck Institute for Astronomy in Heidelberg, Germany, lead author of a paper that will appear in a forthcoming issue of the Astrophysical Journal. "We weren't looking specifically for these galaxies, but they stood out because of their unusual colours."
The observations were part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS), an ambitious three-year survey to analyse the most distant galaxies in the Universe. CANDELS is the first census of dwarf galaxies at such an early epoch on the Universe's history.
"In addition to the images, Hubble has captured spectra from a handful of these galaxies that show us the detailed physics of what's happening within them and confirm their extreme star-forming nature," says co-author Amber Straughn at NASA's Goddard Space Flight Center in Greenbelt, USA.
The observations of ancient galaxies are somewhat at odds with recent detailed studies of the dwarf galaxies that are currently orbiting the Milky Way.
"Those studies suggest that star formation was a relatively slow process, stretching out over billions of years," explains Harry Ferguson of the Space Telescope Science Institute (STScI) in Baltimore, USA, 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."
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