Pushing the world’s biggest ground-based telescopes to their limits, astronomers have peered deep into cosmic history and spied something they shouldn’t have: grizzled old galaxies in an epoch when only infant swarms of stars were thought to exist.
The perplexing discovery, reported in today’s issue of the journal Nature by two separate teams, could force scientists to scrap dearly held theories about how our Milky Way and other galaxies came to be.
“Up until now, we assumed that galaxies were just beginning to form between 8 and 11 billion years ago, but what we found suggests that is not the case,” said astronomer Karl Glazebrook of Johns Hopkins University, who led one of the research teams.
Gregory Wirth, an astronomer at the W.M. Keck Observatory in Hawaii, who did not participate in the studies, called the teams’ findings significant. “What this is telling us is our picture of how galaxies form is incomplete,” he said.
First proposed in 1984, the leading theory of galaxy formation is known as the “hierarchical model.” It states that the menagerie of massive galaxies we have today coalesced over time from smaller groupings of stars.
According to theory, this process should have required billions of years. But that doesn’t jibe with what Glazebrook and his colleagues found using the Gemini North Telescope in Mauna Kea, Hawaii.
To peer back into time, the astronomers took advantage of the fact that the more distant an object is in space, the older it is. This is so because the speed of light is constant. So when astronomers view a distant star or galaxy they are seeing it not as it exists today, but as it looked millions or billions of years ago, when the light left the object.
By capturing faint starlight from the fringes of the cosmos, Glazebrook and his team were able to study galaxies as they looked just 3 billion to 6 billion years after the Big Bang, the fiery explosion thought to have given rise to the universe about 14 billion years ago.
What they saw surprised them. Rather than seeing collections of infant or adolescent stars, they found galaxies not unlike those that exist today.
“There are obviously some aspects of the early lives of galaxies that we don’t yet completely understand,” said Glazebrook, whose team reported some of its results earlier this year at a meeting of the American Astronomical Society. “We do find fewer massive galaxies in the past, but there are still more than we expected.”
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