Ultra-bright galaxies in the early universe may be less common than previously thought, a study conducted using the Hubble Space Telescope has found.
Researchers led by the University of Melbourne in Australia used Hubble to observe two galaxies thought to be so distant that we see them more than 13 billion years back in time when the universe was young.
Published in the Astrophysical Journal Letters, the study found that one galaxy was a bright source seen more than 13 billion years ago, as expected.
However, the other was an "impostor" - a relatively nearby galaxy mistaken for one very far away due to its red colour.
The effect known as redshift gives distant galaxies distinct colours that can indicate how far away they are.
However, some relatively nearby galaxies have deceptively similar colours, lending some uncertainty to their estimated distance.
The researchers said this discovery - that the brightest known galaxy candidate in the early universe is essentially a fraud - has profound implications for models of how galaxies formed when the universe was in its infancy.
Associate Professor Michele Trenti from the University of Melbourne said that while another camera was in use, the team used the highly sensitive Wide Field Camera 3 to observe a random patch of sky for a few hours.
He said repeating this more than 100 times built up a rich dataset that covers unrelated universe parts, maximising the chances of landing a rare, bright, young galaxy.
"Since Hubble primary time is so scarce and oversubscribed, the BoRG survey represents an ideal opportunity to carry out cutting-edge science at no extra cost," Trenti said.
"It is essentially doubling the productivity of an already amazing telescope," said.
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