‘Red nuggets’ near earth shed new light on galactic evolution

14 Sep 2013

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Astronomers have discovered unusually small galaxies densely packed with red stars – or 'red nuggets' as they are called – close to the Earth, an area from where they were previously thought to have vanished.

The new research shows that the red nuggets didn't disappear completely as was previously thought, but were simply hidden within the data of previous surveys.

The red nuggets may shed new light on the evolutionary path of galaxies, the US astronomers who made the discovery say.

In 2005, the Hubble Space Telescope found unusually small galaxies densely packed with red stars in the distant, young universe because they are small and red and also as their existence challenged current theories of galaxy formation, making them precious in astronomers' eyes.

But astronomers had been puzzled why none of these objects, dubbed "red nugget" galaxies, were seen nearby our own Milky Way galaxy, and wondered if they had disappeared over time.

New analysis of data from the Sloan Digital Sky Survey conducted by a telescope in New Mexico showed they hadn't disappeared completely, but rather were hiding in plain sight, concealed within the data of previous astronomical surveys.

Red nugget galaxies are so small that they appear like stars in photographs from ground-based telescopes, the researcher said, but their spectra give away their true nature.

"Looking for 'red nuggets' in the Sloan Digital Sky Survey was like panning a riverbed, washing away silt and mud to uncover bits of gold," Ivana Damjanov of the Harvard-Smithsonian Center for Astrophysics said.

By sifting through the Sloan data, the team identified more than 600 "red nugget" candidates located at distances of 2.5 billion to 5.7 billion light years from Earth – relatively close, as inter-stellar distances go.

The most massive "red nuggets" weigh up to 10 times more than the Milky Way but are up to 10 times smaller than our galaxy.

They could represent a missing link between distant "red nuggets" and nearby elliptical galaxies, the researchers said, and may help explain how small, compact galaxies age over time and become "seeds" for the monster elliptical galaxies seen throughout the universe today.

"We think there are more of these red nuggets, or compact galaxies, hidden in the universe, waiting to be discovered," study co-author Ho Seong Hwang said.

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