Astronomers announced Jan. 7 that they've just discovered a mysterious static coming from everywhere in the sky, apparently. It's coming from the edge of the universe. And they have no clue what it is.
Whoa! That's so 1960s. That's when Bell Labs radio astronomers Arno Penzias and Robert Wilson discovered the cosmic microwave background radiation – a constant hiss picked up by a microwave antenna they were testing. The hiss came from everywhere in the sky, and they wanted to get rid of it. But they couldn't. As it turns out, it represents the feeble afterglow of the Big Bang. And its discovery scored the two scientists a Nobel Prize.
It remains to be seen what this latest discovery means. (A more-formal presentation of the results appears here.) The team that announced it has sent out an SOS to the whiteboard-and-marker types – the theorists – to try to come up with a plausible explanation. But whatever the cause, the results present astrophysicists with something they dearly love: a new, inexplicable (for now) puzzle.
The story begins in July 2006, when a team of scientists launched a remarkable balloon into the skies over Palestine, Texas. Their project is called ARCADE. It aims, among other things, to hunt for the vanishingly faint signatures of heat from the first stars that populated the early universe roughly a billion years after the Big Bang.
The balloon drags a 6,000-pound payload up with it. The payload? Seven sensitive radiometers kept at near absolute zero by 500 gallons of liquid helium, all encased in a special container known in the biz as a dewar. The radiometers scan the sky and measure the strength of the radiation they receive at several radio frequencies. The data are used to generate a map of radio sources that stand out against the cosmic microwave background.
Instead of the heat signatures they were hunting, "to our surprise we found an unexplained radio static ... that fills the early universe," Dr. Kogut says. It was much too intense to be the first stars, and even too intense to be the accumulated radio static from all of the galaxies in the radiometers' view.
How real is this?
Like Penzias and Wilson, Kogut and his colleagues spent roughly a year trying to get rid of the static. They hunted for glitches in their instruments and in the way they processed their data. That didn't do it.
Then they pored over previous results from radiotelescopes that scanned the skies at lower frequencies than the ones the team was using. To their surprise, the older data, some dating as far back as 1981, held hints that the static the ARCADE team found might be easier to pick up at the higher frequencies the team used. So that was a form of confirmation.
Finally, the team explored the possibility that what they'd picked up actually was local, some sort of astrophysical source in or near our galaxy, the Milky Way. But no source is known or predicted to exist that would yield the distribution of static the team recorded.
The signal strength of the mystery static is six time higher than the combined radio emissions of all other sources in the universe.
ARCADE looked at only 7 percent of the sky during its 2006 flight. It will take additional flights, more measurements from a new generation of radiotelescopes, or even more observations from existing ones at lower frequencies to flesh out the picture.
What could be giving these folks all that static? Michael Seiffert, a scientist at the Jet Propulsion Laboratory in Pasadena, Calif., and a member of the team almost refuses to hazard a guess. "We really don't know," he said during a press briefing on the topic at the winter meeting of the American Astronomical Society in Long Beach, Calif.
Searching for an explanation
But one highly speculative idea, he continues, involves the early generation of stars the team was hunting.
The static might be some other kind of emission from these stars, which are thought to have been enormous – something like 300 to 500 times the mass of the sun.
Astrophysicists already know that supermassive black holes in the center of young, active galaxies can spew jets of material for distances of several thousand light-years from their galaxies' cores.
Those jets give off strong radio emissions. Perhaps something similar is happening when these enormous stars – whose lives would be measured in millions of years, not billions – collapse into black holes. They may briefly spew high-energy jets from their north and south poles.
Whatever the ultimate cause of the static, the bottom line, Kogut says, is that: "Even though this prevented us from seeing the heat signatures we were looking for form the first stars, it is exciting evidence of something new and interesting going on in the cosmos."