White Noise

January 08, 2009

Radio static is nobody's friend. There's a lot of interference in the Los Angeles airwaves, for example, which is why I'll be inching along the road at 15 MPH, escaping the tedium by grooving to my favorite tune, when I suddenly hit a trouble spot, and the song gets drowned out by static for a few seconds. Don't you just hate that? I sure do.

NASA hates static even more, since so many of its instruments monitor the heavens using radio waves. One of those is the balloon-borne ARCADE (Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission), launched back in June 2006, rising to 120,000 feet (the point where the Earth's atmosphere thins into the vacuum of space). Once there, it just hung out for awhile, collecting data. Its mission: to search the sky for heat from the first generation of stars.

That sounds straightforward enough, but the big ARCADE-related news at this week's meeting of the American Astronomical Society in Long Beach was the uncovering of a cosmic puzzle. Let's just say that once again, the universe threw one hell of a curve ball.

The ARCADE scientists expected to detect a faint signal, but instead, their instruments picked up a "booming noise six times louder than anyone had predicted." And they have no idea where it's coming from. It certainly doesn't rise from any of the usual sources of radio emissions, like all that gas milling about the outer halo of our Milky Way. While some galaxies emit radio waves to create a sort of background hiss, there aren't really enough such galaxies out there to account for such a strong signal. "You'd have to pack them int the universe like sardines," said team member Dale Fixsen of the University of Maryland, College Park. "There wouldn't be any space left between one galaxy and the next."

What's it all mean? Well, it just got that much harder to listen to the universe, for starters, and by extension, harder to detect those elusive primordial stars that formed some 13 billion years ago, shortly after the Big Bang. But there are some bright spots. It was a nice result for ARCADE, the first instrument capable of measuring the radio sky precisely enough to even detect this signal. (The secret: 500 gallons of ultra-cold liquid helium. bringing the operating temperature down to 2.7 degrees above absolute zero 00 just like the cosmic microwave background radiation, which now could not contaminate the signal.)

And another team member, Jet Propulsion Lab's Michael Seiffert, pointed out that all that cosmic white noise might contain clues to how galaxies developed when the universe was half its present age. For Seiffert, there is no downside. "This is what makes science so exciting," he said. "You start out on a path to measure something -- in this case, the heat from the very first stars -- but run into something else entirely, something unexplained."

So much for scientists being know-it-alls. They're happiest with a big cosmic mystery to solve.

Photo: Artist's rendering of ARCADE. Source: NASA/ARCADE/Roen Kelly

Comments

[Leslie Abraham]

The perimeter of the atmosphere is acting as a lens would and as such is focusing and amplifying the signal strength. When I walk through the curved archway between my living room and kitchen, I have noticed that the sound coming from my speakers are significantly amplified.

[Amiya]

Excellent article. The static (noise) reminded me of how Penzias and Wilson got to the core of Friedman's assumption that the universe looked same from all sides.