Early galaxy formed stars at blistering pace
Peering deep into the universe, scientists have discovered the earliest known starburst galaxy — a revved-up stellar factory popping out stars thousands of times faster than the Milky Way.
The find, described in Thursday’s edition of the journal Nature, could help alter scientists’ understanding of the early evolution of galaxies and larger structures in the universe.
The galaxy, named HFLS 3, existed about 880 million years after the big bang, when the universe was about 6% of its current age, astronomers say. And it’s churning out stars with sun-sized mass at the incredible rate of roughly 2,900 per year.
A typical starburst galaxy may produce the equivalent of hundreds of suns per year, scientists said. The Milky Way, by comparison, creates about two suns annually.
Starburst galaxies are relatively rare. They’re thought to be the ancestors of massive elliptical galaxies, the blob-like clusters of stars that, together with spiral galaxies like the Milky Way, account for most of the universe’s galactic population.
Some scientists think most galaxies may go through an adolescent starburst phase — a spurt of intensive star growth that creates most of a galaxy’s stars before it settles down into adulthood. Such periods are thought to be brief by galactic standards, lasting about 100 million years and making them very exciting to study, scientists said.
When researchers caught sight of HFLS 3, they knew there was something strange about it, said Cornell University astronomer Dominik Riechers, lead author of the Nature study.
“This galaxy looked different from all the others that we’ve seen in the sense that it looked redder than the others,” Riechers said. Light stretches as the universe expands, becoming “redder,” and scientists use this fact to measure cosmic distances. The light from this galaxy had traveled a very long distance before reaching the European Space Agency’s orbiting Herschel Space Observatory, he said.
With gas and dust filling the space between Earth and the unusual galaxy, the scientists could not get a clear read on it. They followed up using a suite of ground-based telescopes, focusing on the radio waves emanating from the galaxy. Unlike visible light, the longer radio waves can punch through layers of gas and dust, giving scientists a clearer portrait of the galaxy.
Their measurements showed that the starburst galaxy was older than any such galaxy seen before.
Cosmologists had thought starburst galaxies proliferated about 3 billion years after the big bang, after matter had enough time to accumulate and collect into deep pockets that could produce young stars at such fast rates.
But discoveries using the Atacama Large Millimeter/submillimeter Array radio telescope in Chile showed that the galactic baby boom may have taken place about 1 billion years earlier, according to a report last month in Nature.
The new study hints that this process got started even sooner.
“It is surprising,” said Chris Carilli, a radio astronomer at the National Radio Astronomy Observatory in Socorro, N.M., who was not involved in the study. “Things can take a long time, and all the gas needs to pile up and then go boom — and yet they’re seeing this 880 million years after the big bang. How did it all go so fast? That’s a fascinating question.”
Mark Swinbank, an astronomer at Durham University in England who was not involved in the study either, said this early starburst galaxy was a fascinating case study. But he was quick to point out that astronomers won’t be able to draw any solid conclusions about these early star-forming galaxies unless dozens more are found relatively close to the big bang.
The scientists also discovered a thick node of dark matter associated with the starburst galaxy — one big enough to grow a present-day galaxy cluster. That could provide them with an early look at how these large-scale structures may have formed early in the universe’s history, researchers said.
As scientists keep searching for starburst galaxies, radio telescopes will reign supreme, Carilli said.
“It’s a new ballgame,” he said.
