Early galaxies sported a modern look
Old is new A survey of some of the earliest galaxies in the universe by the Hubble Space Telescope has found they looked surprisingly similar to those forming more recently.
The survey results, to appear in the Astrophysical Journal, raises questions about how these galaxies could have evolved within the first two billion years of the universe.
Galaxies are classified into several broad groups based on their shape and colour, such as spiral galaxies and elliptical galaxies, known as the Hubble Sequence.
Study lead author, BoMee Lee of the University of Massachusetts, says the key question many astronomers wanted answered is, "when, and over what timescale, did the Hubble Sequence form?"
"To do this you need to peer at distant galaxies and compare them to their closer relatives, to see if they too can be described in the same way."
To find out, Lee and colleagues used data from the longest Hubble survey ever carried out.
Previous observations only looked at ultra-violet light, which had been stretched into visible wavelengths by the expansion of the universe. Consequently astronomers were only seeing places full of very massive short-lived stars, which make galaxies look strange, jagged and blotchy.
This latest study looked at visible light, which had been stretched to infra-red wavelengths, allowing astronomers to see average Sun-like stars - the same stars that we commonly see in more recent nearby galaxies.
What they saw were galaxies that were similar in size and appearance to those around today.
That poses a huge puzzle according to Dr Paul Francis of the Australian National University's Mount Stromlo Observatory, because theories predict that galaxies should look very different early in the evolution of the universe.
"The new data is making clear that these galaxies look very much like our own, which is odd, because they shouldn't have had time to form," says Francis.
"They look like they're in some ways very old, which is odd because the universe wasn't that old back then. And they seem to have settled down to sedate middle age, even though the universe was so young."
What is different is the ratios of the two main types of galaxies observed in the new data.
While the authors are still seeing elliptical and spiral galaxies like today's universe, it seems there were far fewer ellipticals and more spirals galaxies.
According to Francis, elliptical galaxies shouldn't have formed at all so far back in time. Just as weird are indications that some elliptical galaxies became very massive very quickly.
"One idea is that you form the big galaxies first, and the little ones form later," says Francis.
"Another idea is that you get the small galaxies first, and they collide together to form the big ones."
"This seems to be implying that it's the big ones that form first. It's a bit of a puzzle."