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Hubble finds dwarf galaxies formed many of Universe's stars

Jenny Winder, News Writer
Jun 22, 2014, 15:00 UTC

Sen—New observations from the Hubble Space Telescope show that small galaxies, also known as dwarf galaxies, have been responsible for forming a large proportion of the Universe's stars.

Some faint dwarf galaxies that resided in the early Universe, between two and six billion years after the Big Bang, when most of the stars in the universe were formed, underwent a ferociously fast rate of star formation called "starbursts".

Astronomers are striving to deduce dwarf galaxies' contribution to star formation by looking back in time at this crucial era of the Universe's history.

A team conducted a study using data from Hubble's Wide Field Camera 3 (WFC3) to take a big step forward in understanding this formative era by examining a sample of starburst galaxies in the young Universe. They found starburst galaxies to be forming stars at a rate far above what is considered by experts to be a normal rate of star formation.

Understanding the link between a galaxy's mass and its star-forming activity helps to assemble a consistent picture of events in the early Universe. Previous studies of star-forming galaxies were restricted to the analysis of mid- or high-mass galaxies, leaving out the numerous dwarf galaxies that existed in this era of prolific star formation.

This image shows a region of space containing a sample of faint dwarf galaxies (marked by the red circles) studied by NASA's Hubble Space Telescope. The image is part of the Great Observatories Origins Deep Survey (GOODS) Image credit: NASA, ESA, the GOODS Team, and M. Giavalisco (University of Massachusetts, Amherst)

The infrared capabilities of WFC3 have allowed astronomers to finally calculate how much these low-mass dwarf galaxies contributed to the star population in our Universe.

"We already suspected these kinds of galaxies would contribute to the early wave of star formation, but this is the first time we've been able to measure the effect they actually had," said Hakim Atek of the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland, lead author of the study. "They appear to have had a surprisingly huge role to play."

Studying this early epoch of the universe's history is critical to fully understanding how these stars formed and how galaxies have grown and evolved 2 billion to 6 billion years after the beginning of the Universe.

"These galaxies are forming stars so quickly that they could actually double their entire mass of stars in only 150 million years—an incredibly short astronomical timescale," said co-author Jean-Paul Kneib, also of EPFL.

Researchers say such a mass gain would take most normal galaxies one billion to three billion years to accomplish.

It is unusual to find a galaxy in a state of starburst, which suggests to researchers that starburst galaxies are the result of an unusual incident in the past, such as a violent merger.

This finding may also help to unravel the secrets of galactic evolution. As galaxies merge, they are consumed by newly formed stars that feed on their combined gases, and exploding stars and supermassive black holes emit galactic material, a process that depletes the mass of a galaxy.

A paper about the team's findings has been published in The Astrophysical Journal.

A Hubblecast video about the new findings. Credit: Hubble/ESA