Radio Noise Pollution

It’s Not Just About the Neighbors

A while back, I wrote an article for a book called State of the Universe 2008, and in it I discuss how some local astronomers were hunting for the very faint and elusive signals from the 327 MHz deuterium line out in space. This may sound rather esoteric — and it is if your life doesn’t revolve around trying to find out how much deuterium is left over in the cosmos after 13.7 billion years of stellar formation (which destroys deuterium).  For astronomers however, this is an important quantity to know since all the deuterium that ever existed in the cosmos was made in the Big Bang. If you find deuterium in great quantities somewhere, then it’s a pretty good sign that there’s been no stellar activity to suck it up.

The signal for deuterium (327 MHz) is detectable, but only just barely. And, if there’s any kind of radio frequency interference (RFI) in the vicinity of the detector, then it wipes out the deuterium signal. And I do mean ANY kind of signal — including RFI from sound systems, door bells, radios, cell phones, and answering machines.  The folks at MIT Haystack Observatory built a deuterium array and then spent months “mitigating” RFI from the nearby homes. It was worth it: these scientists were the first to detect and confirm this material.

But, they aren’t the only radio astronomers to be affected by nearby noise. Just like radio astronomers around the world, the folks at Greenbank, West Virginia (home of a major radio observatory) are constantly fighting RFI from things as simple as a car engine or a heat pad on somebody’s bed.  The signals they track down from earth-based sources are often more than strong enough to wipe out the faint frequencies emanating from distant pulsars and other cosmic sources.

This is why radio observatories have radio-quiet zones around them. And inside those zones, people can’t use technology that interferes with the faint signals from space. I’ve visited facilities where we’ve been asked to turn off cell phones, not use digital cameras, and refrain from turning on the wireless transmitters on our laptop computers. As annoying as it might be to visitors or the neighbors, having an RFI-free environment for science is important. The alternative is to move the observatories away from where they are (with the concomitant loss of jobs, etc.) and try to find other radio-quiet places (which the folks who are building the MWA and ALMA are doing). On a planet where there’s hardly anywhere left unexplored and unsettled, that’s getting to be a tough (and expensive) proposition.