An ingenious technique reveals data that's been lost for 11 billion years
Presidential tracking polls are famous for their speed—a gaffe at noon is reflected in the numbers by four. That’s because a poll is not a lengthy conversation with voters, but just a quick-hit piece of data-gathering repeated over and over. The same approach now appears able to give us answers about the universe, too.
Using just four hours of telescope observation time, astronomers have generated a new image of what part of the universe looked like in its adolescence, when it was less than a quarter of its current age. The three-dimensional map, published in The Astrophysical Journal Letters, measures millions of light years across and reveals regions of high-density matter representing galaxies as they were barely 3 billion years post-Big Bang.
“We’ve pulled this off a decade before anyone else thought it was possible,” said Max Planck postdoctoral researcher Khee-Gan Lee, the paper’s lead author.
Astronomers had previously believed they would need far more observation time and more-powerful telescopes than are currently available to collect sufficient starlight from distant galaxies with which to do a job like this. That’s partly because those light sources appear up to 15 billion times dimmer than the very faintest stars that can be seen with the naked eye.
But four hours on the Keck I telescope at the Keck Observatory on Mauna Kea, Hawaii turned out to be enough. The scientists used a technique similar to a CT scan to create their map. But rather than taking cross-sectional x-rays through a body to generate a 3D image, they used light from background galaxies passing through hydrogen gas in the “cosmic web”—the tangle of macro-filaments in which the universe’s matter arranges itself—to do the same thing.
The reason they didn’t need the most sensitive equipment available to do this work was because they had a powerful algorithm instead, created by graduate student Casey Stark and physics and astronomy professor Martin White, both of the University of California, Berkeley. The data they gathered might have been noisy but the algorithm cleaned it right up. The resulting map, says Ohio State University professor of astronomy David Weinberg, is “fine enough that it’s revealing a lot of the interesting details.”
Adds Harvard astronomy professor Daniel Eisenstein, “For a lot of questions, this is a very useful scale of a map.”
The map’s elongated, plank-like shape reflects one admitted constraint of the study: because of bad weather and the short data collection time, the astronomers could map only a limited volume of space. The next order of business is for Keck I to cover a larger patch of sky, revealing huge swathes of the adolescent universe. From this map astronomers will not just be able to see the appearance of the cosmos a short while after the Big Bang, but also tease out a little bit of information about the clumping of matter that allowed galaxies to form in some regions while leaving others empty.
Next-generation super-telescopes will no doubt be useful for both these questions, able to quadruple the density of the data as well as help scientists figure out how the universe looked even closer to the Big Bang than 11 billion years ago. For now, though, telescopes like Keck I will tell us plenty. “Noisy data doesn’t scare me,” Lee said.