Tuning in to the cosmic radio

BY DR EMILY BALDWIN

ASTRONOMY NOW

Posted: 09 January, 2009

According to scientists presenting their work at the American Astronomical Society meeting this week, cosmic radio noise booms six times louder than expected, potentially drowning out the sounds of the early Universe.

Scientists made the discovery using the ballon-borne ARCADE instrument, or Absolute Radiometer for Cosmology, Astrophysics and Diffuse Emission, which has resided at an altitude of 36 kilometres – the boundary between the Earth’s atmosphere and the vacuum of space – since July 2006. The aim of the mission was to search the sky for heat from the first generation of stars, but instead, it uncovered an interesting phenomenon.

ARCADE viewed about 7 percent of the sky, represented by the coloured region on this all-sky radio map. The plane of the Milky Way, runs across the centre. Image: NASA/ ARCADE.

"The Universe really threw us a curve," says team leader Alan Kogut of NASA’s Goddard Space Flight Center. "Instead of the faint signal we hoped to find, here was this booming noise six times louder than anyone had predicted."

Many objects in the Universe emit radio waves, including gas in the outermost halo of our own Milky Way Galaxy and primordial stars, but the source of this cosmic radio background is baffling scientists. Team member Dale Fixsen of the University of Maryland says that there just aren’t enough radio galaxies to account for the signal ARCADE detected. "You'd have to pack them into the Universe like sardines," he says. "There wouldn't be any space left between one galaxy and the next."

While the problem of this radio excess is an exciting discovery in itself, it comes with some serious implications. The pirate radio static that is controlling the cosmic airwaves could be drowning out the much sought after signal of the earliest stars of the Universe, thought to have formed shortly after the Big Bang 13.7 billion years ago. It’s not all bad news, however, for the static could provide important clues to the development of galaxies and radio sources in the Universe’s infancy.

"This is what makes science so exciting," says Michael Seiffert of NASA's Jet Propulsion Laboratory. "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."

ARCADE discovered a screen of extra-loud cosmic static (represented by the white band at the top of this illustration) that is blocking the heat from the first stars. Image: NASA/ARCADE/Roen Kelly.

ARCADE is the first instrument to measure the radio sky with enough precision to detect this curious signal. It operates at the same temperature as the cosmic microwave background radiation, the remnant heat of the Big Bang, just 2.7 degrees above absolute zero. "If ARCADE is the same temperature as the microwave background, then the instrument's heat cannot contaminate the cosmic signal," explains Kogut.

Four papers describing various aspects of ARCADE’s discovery have been submitted to The Astrophysical Journal.

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